Published by the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being “Copying”, with the Front-Cover texts being “A GNU Manual”, and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License”.
(a) The FSF's Back-Cover Text is: “You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.”
This Info file contains edition 2.8 of the GNU Emacs Lisp Reference Manual, corresponding to GNU Emacs version 21.2.
Appendices
--- The Detailed Node Listing ---
Here are other nodes that are inferiors of those already listed, mentioned here so you can get to them in one step:
Introduction
Conventions
Tips and Conventions
Format of Descriptions
Lisp Data Types
Programming Types
List Type
Editing Types
Numbers
Strings and Characters
Lists
Modifying Existing List Structure
Sequences, Arrays, and Vectors
Symbols
Evaluation
Kinds of Forms
Control Structures
Nonlocal Exits
Errors
Variables
Scoping Rules for Variable Bindings
Buffer-Local Variables
Functions
Lambda Expressions
Macros
Loading
Byte Compilation
Advising Functions
Debugging Lisp Programs
The Lisp Debugger
Debugging Invalid Lisp Syntax
Reading and Printing Lisp Objects
Minibuffers
Completion
Command Loop
Defining Commands
Keymaps
Major and Minor Modes
Major Modes
Minor Modes
Mode Line Format
Documentation
Files
Visiting Files
Information about Files
File Names
Backups and Auto-Saving
Backup Files
Buffers
Windows
Frames
Positions
Motion
Markers
Text
The Kill Ring
Indentation
Text Properties
Non-ASCII Characters
Searching and Matching
Regular Expressions
Syntax Tables
Syntax Descriptors
Abbrevs And Abbrev Expansion
Processes
Receiving Output from Processes
Operating System Interface
Starting Up Emacs
Getting out of Emacs
Emacs Display
GNU Emacs Internals
Object Internals
Most of the GNU Emacs text editor is written in the programming language called Emacs Lisp. You can write new code in Emacs Lisp and install it as an extension to the editor. However, Emacs Lisp is more than a mere “extension language”; it is a full computer programming language in its own right. You can use it as you would any other programming language.
Because Emacs Lisp is designed for use in an editor, it has special features for scanning and parsing text as well as features for handling files, buffers, displays, subprocesses, and so on. Emacs Lisp is closely integrated with the editing facilities; thus, editing commands are functions that can also conveniently be called from Lisp programs, and parameters for customization are ordinary Lisp variables.
This manual attempts to be a full description of Emacs Lisp. For a beginner's introduction to Emacs Lisp, see An Introduction to Emacs Lisp Programming, by Bob Chassell, also published by the Free Software Foundation. This manual presumes considerable familiarity with the use of Emacs for editing; see The GNU Emacs Manual for this basic information.
Generally speaking, the earlier chapters describe features of Emacs Lisp that have counterparts in many programming languages, and later chapters describe features that are peculiar to Emacs Lisp or relate specifically to editing.
This is edition 2.8.
This manual has gone through numerous drafts. It is nearly complete but not flawless. There are a few topics that are not covered, either because we consider them secondary (such as most of the individual modes) or because they are yet to be written. Because we are not able to deal with them completely, we have left out several parts intentionally. This includes most information about usage on VMS.
The manual should be fully correct in what it does cover, and it is therefore open to criticism on anything it says—from specific examples and descriptive text, to the ordering of chapters and sections. If something is confusing, or you find that you have to look at the sources or experiment to learn something not covered in the manual, then perhaps the manual should be fixed. Please let us know.
As you use this manual, we ask that you send corrections as soon as you find them. If you think of a simple, real life example for a function or group of functions, please make an effort to write it up and send it in. Please reference any comments to the node name and function or variable name, as appropriate. Also state the number of the edition you are criticizing.
Please mail comments and corrections to
bug-lisp-manual@gnu.org
We let mail to this list accumulate unread until someone decides to
apply the corrections. Months, and sometimes years, go by between
updates. So please attach no significance to the lack of a reply—your
mail will be acted on in due time. If you want to contact the
Emacs maintainers more quickly, send mail to
bug-gnu-emacs@gnu.org.
Lisp (LISt Processing language) was first developed in the late 1950s at the Massachusetts Institute of Technology for research in artificial intelligence. The great power of the Lisp language makes it ideal for other purposes as well, such as writing editing commands.
Dozens of Lisp implementations have been built over the years, each with its own idiosyncrasies. Many of them were inspired by Maclisp, which was written in the 1960s at MIT's Project MAC. Eventually the implementors of the descendants of Maclisp came together and developed a standard for Lisp systems, called Common Lisp. In the meantime, Gerry Sussman and Guy Steele at MIT developed a simplified but very powerful dialect of Lisp, called Scheme.
GNU Emacs Lisp is largely inspired by Maclisp, and a little by Common Lisp. If you know Common Lisp, you will notice many similarities. However, many features of Common Lisp have been omitted or simplified in order to reduce the memory requirements of GNU Emacs. Sometimes the simplifications are so drastic that a Common Lisp user might be very confused. We will occasionally point out how GNU Emacs Lisp differs from Common Lisp. If you don't know Common Lisp, don't worry about it; this manual is self-contained.
A certain amount of Common Lisp emulation is available via the cl library. See Common Lisp Extension.
Emacs Lisp is not at all influenced by Scheme; but the GNU project has an implementation of Scheme, called Guile. We use Guile in all new GNU software that calls for extensibility.
This section explains the notational conventions that are used in this manual. You may want to skip this section and refer back to it later.
Throughout this manual, the phrases “the Lisp reader” and “the Lisp printer” refer to those routines in Lisp that convert textual representations of Lisp objects into actual Lisp objects, and vice versa. See Printed Representation, for more details. You, the person reading this manual, are thought of as “the programmer” and are addressed as “you”. “The user” is the person who uses Lisp programs, including those you write.
Examples of Lisp code are formatted like this: (list 1 2 3).
Names that represent metasyntactic variables, or arguments to a function
being described, are formatted like this: first-number.
nil and t
In Lisp, the symbol nil has three separate meanings: it
is a symbol with the name ‘nil’; it is the logical truth value
false; and it is the empty list—the list of zero elements.
When used as a variable, nil always has the value nil.
As far as the Lisp reader is concerned, ‘()’ and ‘nil’ are
identical: they stand for the same object, the symbol nil. The
different ways of writing the symbol are intended entirely for human
readers. After the Lisp reader has read either ‘()’ or ‘nil’,
there is no way to determine which representation was actually written
by the programmer.
In this manual, we use () when we wish to emphasize that it
means the empty list, and we use nil when we wish to emphasize
that it means the truth value false. That is a good convention to use
in Lisp programs also.
(cons 'foo ()) ; Emphasize the empty list (not nil) ; Emphasize the truth value false
In contexts where a truth value is expected, any non-nil value
is considered to be true. However, t is the preferred way
to represent the truth value true. When you need to choose a
value which represents true, and there is no other basis for
choosing, use t. The symbol t always has the value
t.
In Emacs Lisp, nil and t are special symbols that always
evaluate to themselves. This is so that you do not need to quote them
to use them as constants in a program. An attempt to change their
values results in a setting-constant error. The same is true of
any symbol whose name starts with a colon (‘:’). See Constant Variables.
A Lisp expression that you can evaluate is called a form. Evaluating a form always produces a result, which is a Lisp object. In the examples in this manual, this is indicated with ‘=>’:
(car '(1 2))
=> 1
You can read this as “(car '(1 2)) evaluates to 1”.
When a form is a macro call, it expands into a new form for Lisp to evaluate. We show the result of the expansion with ‘==>’. We may or may not show the result of the evaluation of the expanded form.
(third '(a b c))
==> (car (cdr (cdr '(a b c))))
=> c
Sometimes to help describe one form we show another form that produces identical results. The exact equivalence of two forms is indicated with ‘==’.
(make-sparse-keymap) == (list 'keymap)
Many of the examples in this manual print text when they are
evaluated. If you execute example code in a Lisp Interaction buffer
(such as the buffer ‘*scratch*’), the printed text is inserted into
the buffer. If you execute the example by other means (such as by
evaluating the function eval-region), the printed text is
displayed in the echo area.
Examples in this manual indicate printed text with ‘-|’,
irrespective of where that text goes. The value returned by evaluating
the form (here bar) follows on a separate line.
(progn (print 'foo) (print 'bar))
-| foo
-| bar
=> bar
Some examples signal errors. This normally displays an error message in the echo area. We show the error message on a line starting with ‘error-->’. Note that ‘error-->’ itself does not appear in the echo area.
(+ 23 'x)
error--> Wrong type argument: number-or-marker-p, x
Some examples describe modifications to the contents of a buffer, by showing the “before” and “after” versions of the text. These examples show the contents of the buffer in question between two lines of dashes containing the buffer name. In addition, ‘-!-’ indicates the location of point. (The symbol for point, of course, is not part of the text in the buffer; it indicates the place between two characters where point is currently located.)
---------- Buffer: foo ----------
This is the -!-contents of foo.
---------- Buffer: foo ----------
(insert "changed ")
=> nil
---------- Buffer: foo ----------
This is the changed -!-contents of foo.
---------- Buffer: foo ----------
Functions, variables, macros, commands, user options, and special forms are described in this manual in a uniform format. The first line of a description contains the name of the item followed by its arguments, if any. The category—function, variable, or whatever—appears at the beginning of the line. The description follows on succeeding lines, sometimes with examples.
In a function description, the name of the function being described appears first. It is followed on the same line by a list of argument names. These names are also used in the body of the description, to stand for the values of the arguments.
The appearance of the keyword &optional in the argument list
indicates that the subsequent arguments may be omitted (omitted
arguments default to nil). Do not write &optional when
you call the function.
The keyword &rest (which must be followed by a single argument
name) indicates that any number of arguments can follow. The single
following argument name will have a value, as a variable, which is a
list of all these remaining arguments. Do not write &rest when
you call the function.
Here is a description of an imaginary function foo:
The function
foosubtracts integer1 from integer2, then adds all the rest of the arguments to the result. If integer2 is not supplied, then the number 19 is used by default.(foo 1 5 3 9) => 16 (foo 5) => 14More generally,
(foo w x y...) == (+ (- x w) y...)
Any argument whose name contains the name of a type (e.g., integer, integer1 or buffer) is expected to be of that type. A plural of a type (such as buffers) often means a list of objects of that type. Arguments named object may be of any type. (See Lisp Data Types, for a list of Emacs object types.) Arguments with other sorts of names (e.g., new-file) are discussed specifically in the description of the function. In some sections, features common to the arguments of several functions are described at the beginning.
See Lambda Expressions, for a more complete description of optional and rest arguments.
Command, macro, and special form descriptions have the same format, but the word `Function' is replaced by `Command', `Macro', or `Special Form', respectively. Commands are simply functions that may be called interactively; macros process their arguments differently from functions (the arguments are not evaluated), but are presented the same way.
Special form descriptions use a more complex notation to specify optional and repeated arguments because they can break the argument list down into separate arguments in more complicated ways. ‘[optional-arg]’ means that optional-arg is optional and ‘repeated-args...’ stands for zero or more arguments. Parentheses are used when several arguments are grouped into additional levels of list structure. Here is an example:
This imaginary special form implements a loop that executes the body forms and then increments the variable var on each iteration. On the first iteration, the variable has the value from; on subsequent iterations, it is incremented by one (or by inc if that is given). The loop exits before executing body if var equals to. Here is an example:
(count-loop (i 0 10) (prin1 i) (princ " ") (prin1 (aref vector i)) (terpri))If from and to are omitted, var is bound to
nilbefore the loop begins, and the loop exits if var is non-nilat the beginning of an iteration. Here is an example:(count-loop (done) (if (pending) (fixit) (setq done t)))In this special form, the arguments from and to are optional, but must both be present or both absent. If they are present, inc may optionally be specified as well. These arguments are grouped with the argument var into a list, to distinguish them from body, which includes all remaining elements of the form.
A variable is a name that can hold a value. Although any variable can be set by the user, certain variables that exist specifically so that users can change them are called user options. Ordinary variables and user options are described using a format like that for functions except that there are no arguments.
Here is a description of the imaginary electric-future-map
variable.
The value of this variable is a full keymap used by Electric Command Future mode. The functions in this map allow you to edit commands you have not yet thought about executing.
User option descriptions have the same format, but `Variable' is replaced by `User Option'.
These facilities provide information about which version of Emacs is in use.
This function returns a string describing the version of Emacs that is running. It is useful to include this string in bug reports.
(emacs-version) => "GNU Emacs 20.3.5 (i486-pc-linux-gnulibc1, X toolkit) of Sat Feb 14 1998 on psilocin.gnu.org"Called interactively, the function prints the same information in the echo area.
The value of this variable indicates the time at which Emacs was built at the local site. It is a list of three integers, like the value of
current-time(see Time of Day).emacs-build-time => (13623 62065 344633)
The value of this variable is the version of Emacs being run. It is a string such as
"20.3.1". The last number in this string is not really part of the Emacs release version number; it is incremented each time you build Emacs in any given directory. A value with four numeric components, such as"20.3.9.1", indicates an unreleased test version.
The following two variables have existed since Emacs version 19.23:
The major version number of Emacs, as an integer. For Emacs version 20.3, the value is 20.
The minor version number of Emacs, as an integer. For Emacs version 20.3, the value is 3.
This manual was written by Robert Krawitz, Bil Lewis, Dan LaLiberte, Richard M. Stallman and Chris Welty, the volunteers of the GNU manual group, in an effort extending over several years. Robert J. Chassell helped to review and edit the manual, with the support of the Defense Advanced Research Projects Agency, ARPA Order 6082, arranged by Warren A. Hunt, Jr. of Computational Logic, Inc.
Corrections were supplied by Karl Berry, Jim Blandy, Bard Bloom, Stephane Boucher, David Boyes, Alan Carroll, Richard Davis, Lawrence R. Dodd, Peter Doornbosch, David A. Duff, Chris Eich, Beverly Erlebacher, David Eckelkamp, Ralf Fassel, Eirik Fuller, Stephen Gildea, Bob Glickstein, Eric Hanchrow, George Hartzell, Nathan Hess, Masayuki Ida, Dan Jacobson, Jak Kirman, Bob Knighten, Frederick M. Korz, Joe Lammens, Glenn M. Lewis, K. Richard Magill, Brian Marick, Roland McGrath, Skip Montanaro, John Gardiner Myers, Thomas A. Peterson, Francesco Potorti, Friedrich Pukelsheim, Arnold D. Robbins, Raul Rockwell, Per Starbäck, Shinichirou Sugou, Kimmo Suominen, Edward Tharp, Bill Trost, Rickard Westman, Jean White, Matthew Wilding, Carl Witty, Dale Worley, Rusty Wright, and David D. Zuhn.
A Lisp object is a piece of data used and manipulated by Lisp programs. For our purposes, a type or data type is a set of possible objects.
Every object belongs to at least one type. Objects of the same type have similar structures and may usually be used in the same contexts. Types can overlap, and objects can belong to two or more types. Consequently, we can ask whether an object belongs to a particular type, but not for “the” type of an object.
A few fundamental object types are built into Emacs. These, from which all other types are constructed, are called primitive types. Each object belongs to one and only one primitive type. These types include integer, float, cons, symbol, string, vector, hash-table, subr, and byte-code function, plus several special types, such as buffer, that are related to editing. (See Editing Types.)
Each primitive type has a corresponding Lisp function that checks whether an object is a member of that type.
Note that Lisp is unlike many other languages in that Lisp objects are self-typing: the primitive type of the object is implicit in the object itself. For example, if an object is a vector, nothing can treat it as a number; Lisp knows it is a vector, not a number.
In most languages, the programmer must declare the data type of each variable, and the type is known by the compiler but not represented in the data. Such type declarations do not exist in Emacs Lisp. A Lisp variable can have any type of value, and it remembers whatever value you store in it, type and all.
This chapter describes the purpose, printed representation, and read syntax of each of the standard types in GNU Emacs Lisp. Details on how to use these types can be found in later chapters.
The printed representation of an object is the format of the
output generated by the Lisp printer (the function prin1) for
that object. The read syntax of an object is the format of the
input accepted by the Lisp reader (the function read) for that
object. See Read and Print.
Most objects have more than one possible read syntax. Some types of object have no read syntax, since it may not make sense to enter objects of these types directly in a Lisp program. Except for these cases, the printed representation of an object is also a read syntax for it.
In other languages, an expression is text; it has no other form. In Lisp, an expression is primarily a Lisp object and only secondarily the text that is the object's read syntax. Often there is no need to emphasize this distinction, but you must keep it in the back of your mind, or you will occasionally be very confused.
Every type has a printed representation. Some types have no read
syntax—for example, the buffer type has none. Objects of these types
are printed in hash notation: the characters ‘#<’ followed by
a descriptive string (typically the type name followed by the name of
the object), and closed with a matching ‘>’. Hash notation cannot
be read at all, so the Lisp reader signals the error
invalid-read-syntax whenever it encounters ‘#<’.
(current-buffer)
=> #<buffer objects.texi>
When you evaluate an expression interactively, the Lisp interpreter
first reads the textual representation of it, producing a Lisp object,
and then evaluates that object (see Evaluation). However,
evaluation and reading are separate activities. Reading returns the
Lisp object represented by the text that is read; the object may or may
not be evaluated later. See Input Functions, for a description of
read, the basic function for reading objects.
A comment is text that is written in a program only for the sake of humans that read the program, and that has no effect on the meaning of the program. In Lisp, a semicolon (‘;’) starts a comment if it is not within a string or character constant. The comment continues to the end of line. The Lisp reader discards comments; they do not become part of the Lisp objects which represent the program within the Lisp system.
The ‘#@count’ construct, which skips the next count characters, is useful for program-generated comments containing binary data. The Emacs Lisp byte compiler uses this in its output files (see Byte Compilation). It isn't meant for source files, however.
See Comment Tips, for conventions for formatting comments.
There are two general categories of types in Emacs Lisp: those having to do with Lisp programming, and those having to do with editing. The former exist in many Lisp implementations, in one form or another. The latter are unique to Emacs Lisp.
The range of values for integers in Emacs Lisp is −134217728 to
134217727 (28 bits; i.e.,
-2**27
to
2**27 - 1)
on most machines. (Some machines may provide a wider range.) It is
important to note that the Emacs Lisp arithmetic functions do not check
for overflow. Thus (1+ 134217727) is −134217728 on most
machines.
The read syntax for integers is a sequence of (base ten) digits with an optional sign at the beginning and an optional period at the end. The printed representation produced by the Lisp interpreter never has a leading ‘+’ or a final ‘.’.
-1 ; The integer -1. 1 ; The integer 1. 1. ; Also the integer 1. +1 ; Also the integer 1. 268435457 ; Also the integer 1 on a 28-bit implementation.
See Numbers, for more information.
Floating point numbers are the computer equivalent of scientific
notation. The precise number of significant figures and the range of
possible exponents is machine-specific; Emacs always uses the C data
type double to store the value.
The printed representation for floating point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, ‘1500.0’, ‘15e2’, ‘15.0e2’, ‘1.5e3’, and ‘.15e4’ are five ways of writing a floating point number whose value is 1500. They are all equivalent.
See Numbers, for more information.
A character in Emacs Lisp is nothing more than an integer. In other words, characters are represented by their character codes. For example, the character A is represented as the integer 65.
Individual characters are not often used in programs. It is far more common to work with strings, which are sequences composed of characters. See String Type.
Characters in strings, buffers, and files are currently limited to the range of 0 to 524287—nineteen bits. But not all values in that range are valid character codes. Codes 0 through 127 are ascii codes; the rest are non-ascii (see Non-ASCII Characters). Characters that represent keyboard input have a much wider range, to encode modifier keys such as Control, Meta and Shift.
Since characters are really integers, the printed representation of a character is a decimal number. This is also a possible read syntax for a character, but writing characters that way in Lisp programs is a very bad idea. You should always use the special read syntax formats that Emacs Lisp provides for characters. These syntax formats start with a question mark.
The usual read syntax for alphanumeric characters is a question mark followed by the character; thus, ‘?A’ for the character A, ‘?B’ for the character B, and ‘?a’ for the character a.
For example:
?Q => 81 ?q => 113
You can use the same syntax for punctuation characters, but it is often a good idea to add a ‘\’ so that the Emacs commands for editing Lisp code don't get confused. For example, ‘?\ ’ is the way to write the space character. If the character is ‘\’, you must use a second ‘\’ to quote it: ‘?\\’.
You can express the characters Control-g, backspace, tab, newline, vertical tab, formfeed, return, del, and escape as ‘?\a’, ‘?\b’, ‘?\t’, ‘?\n’, ‘?\v’, ‘?\f’, ‘?\r’, ‘?\d’, and ‘?\e’, respectively. Thus,
?\a => 7 ; C-g
?\b => 8 ; backspace, <BS>, C-h
?\t => 9 ; tab, <TAB>, C-i
?\n => 10 ; newline, C-j
?\v => 11 ; vertical tab, C-k
?\f => 12 ; formfeed character, C-l
?\r => 13 ; carriage return, <RET>, C-m
?\e => 27 ; escape character, <ESC>, C-[
?\\ => 92 ; backslash character, \
?\d => 127 ; delete character, <DEL>
These sequences which start with backslash are also known as escape sequences, because backslash plays the role of an escape character; this usage has nothing to do with the character <ESC>.
Control characters may be represented using yet another read syntax. This consists of a question mark followed by a backslash, caret, and the corresponding non-control character, in either upper or lower case. For example, both ‘?\^I’ and ‘?\^i’ are valid read syntax for the character C-i, the character whose value is 9.
Instead of the ‘^’, you can use ‘C-’; thus, ‘?\C-i’ is equivalent to ‘?\^I’ and to ‘?\^i’:
?\^I => 9 ?\C-I => 9
In strings and buffers, the only control characters allowed are those that exist in ascii; but for keyboard input purposes, you can turn any character into a control character with ‘C-’. The character codes for these non-ascii control characters include the 2**26 bit as well as the code for the corresponding non-control character. Ordinary terminals have no way of generating non-ascii control characters, but you can generate them straightforwardly using X and other window systems.
For historical reasons, Emacs treats the <DEL> character as the control equivalent of ?:
?\^? => 127 ?\C-? => 127
As a result, it is currently not possible to represent the character Control-?, which is a meaningful input character under X, using ‘\C-’. It is not easy to change this, as various Lisp files refer to <DEL> in this way.
For representing control characters to be found in files or strings, we recommend the ‘^’ syntax; for control characters in keyboard input, we prefer the ‘C-’ syntax. Which one you use does not affect the meaning of the program, but may guide the understanding of people who read it.
A meta character is a character typed with the <META> modifier key. The integer that represents such a character has the 2**27 bit set (which on most machines makes it a negative number). We use high bits for this and other modifiers to make possible a wide range of basic character codes.
In a string, the 2**7 bit attached to an ascii character indicates a meta character; thus, the meta characters that can fit in a string have codes in the range from 128 to 255, and are the meta versions of the ordinary ascii characters. (In Emacs versions 18 and older, this convention was used for characters outside of strings as well.)
The read syntax for meta characters uses ‘\M-’. For example, ‘?\M-A’ stands for M-A. You can use ‘\M-’ together with octal character codes (see below), with ‘\C-’, or with any other syntax for a character. Thus, you can write M-A as ‘?\M-A’, or as ‘?\M-\101’. Likewise, you can write C-M-b as ‘?\M-\C-b’, ‘?\C-\M-b’, or ‘?\M-\002’.
The case of a graphic character is indicated by its character code; for example, ascii distinguishes between the characters ‘a’ and ‘A’. But ascii has no way to represent whether a control character is upper case or lower case. Emacs uses the 2**25 bit to indicate that the shift key was used in typing a control character. This distinction is possible only when you use X terminals or other special terminals; ordinary terminals do not report the distinction to the computer in any way. The Lisp syntax for the shift bit is ‘\S-’; thus, ‘?\C-\S-o’ or ‘?\C-\S-O’ represents the shifted-control-o character.
The X Window System defines three other modifier bits that can be set in a character: hyper, super and alt. The syntaxes for these bits are ‘\H-’, ‘\s-’ and ‘\A-’. (Case is significant in these prefixes.) Thus, ‘?\H-\M-\A-x’ represents Alt-Hyper-Meta-x. Numerically, the bit values are 2**22 for alt, 2**23 for super and 2**24 for hyper.
Finally, the most general read syntax for a character represents the
character code in either octal or hex. To use octal, write a question
mark followed by a backslash and the octal character code (up to three
octal digits); thus, ‘?\101’ for the character A,
‘?\001’ for the character C-a, and ?\002 for the
character C-b. Although this syntax can represent any ascii
character, it is preferred only when the precise octal value is more
important than the ascii representation.
?\012 => 10 ?\n => 10 ?\C-j => 10
?\101 => 65 ?A => 65
To use hex, write a question mark followed by a backslash, ‘x’,
and the hexadecimal character code. You can use any number of hex
digits, so you can represent any character code in this way.
Thus, ‘?\x41’ for the character A, ‘?\x1’ for the
character C-a, and ?\x8e0 for the Latin-1 character
‘a’ with grave accent.
A backslash is allowed, and harmless, preceding any character without a special escape meaning; thus, ‘?\+’ is equivalent to ‘?+’. There is no reason to add a backslash before most characters. However, you should add a backslash before any of the characters ‘()\|;'`"#.,’ to avoid confusing the Emacs commands for editing Lisp code. Also add a backslash before whitespace characters such as space, tab, newline and formfeed. However, it is cleaner to use one of the easily readable escape sequences, such as ‘\t’, instead of an actual whitespace character such as a tab.
A symbol in GNU Emacs Lisp is an object with a name. The symbol name serves as the printed representation of the symbol. In ordinary use, the name is unique—no two symbols have the same name.
A symbol can serve as a variable, as a function name, or to hold a property list. Or it may serve only to be distinct from all other Lisp objects, so that its presence in a data structure may be recognized reliably. In a given context, usually only one of these uses is intended. But you can use one symbol in all of these ways, independently.
A symbol whose name starts with a colon (‘:’) is called a keyword symbol. These symbols automatically act as constants, and are normally used only by comparing an unknown symbol with a few specific alternatives.
A symbol name can contain any characters whatever. Most symbol names are written with letters, digits, and the punctuation characters ‘-+=*/’. Such names require no special punctuation; the characters of the name suffice as long as the name does not look like a number. (If it does, write a ‘\’ at the beginning of the name to force interpretation as a symbol.) The characters ‘_~!@$%^&:<>{}?’ are less often used but also require no special punctuation. Any other characters may be included in a symbol's name by escaping them with a backslash. In contrast to its use in strings, however, a backslash in the name of a symbol simply quotes the single character that follows the backslash. For example, in a string, ‘\t’ represents a tab character; in the name of a symbol, however, ‘\t’ merely quotes the letter ‘t’. To have a symbol with a tab character in its name, you must actually use a tab (preceded with a backslash). But it's rare to do such a thing.
Common Lisp note: In Common Lisp, lower case letters are always “folded” to upper case, unless they are explicitly escaped. In Emacs Lisp, upper case and lower case letters are distinct.
Here are several examples of symbol names. Note that the ‘+’ in the fifth example is escaped to prevent it from being read as a number. This is not necessary in the sixth example because the rest of the name makes it invalid as a number.
foo ; A symbol named ‘foo’. FOO ; A symbol named ‘FOO’, different from ‘foo’. char-to-string ; A symbol named ‘char-to-string’. 1+ ; A symbol named ‘1+’ ; (not ‘+1’, which is an integer). \+1 ; A symbol named ‘+1’ ; (not a very readable name). \(*\ 1\ 2\) ; A symbol named ‘(* 1 2)’ (a worse name). +-*/_~!@$%^&=:<>{} ; A symbol named ‘+-*/_~!@$%^&=:<>{}’. ; These characters need not be escaped.
Normally the Lisp reader interns all symbols (see Creating Symbols). To prevent interning, you can write ‘#:’ before the name of the symbol.
A sequence is a Lisp object that represents an ordered set of elements. There are two kinds of sequence in Emacs Lisp, lists and arrays. Thus, an object of type list or of type array is also considered a sequence.
Arrays are further subdivided into strings, vectors, char-tables and
bool-vectors. Vectors can hold elements of any type, but string
elements must be characters, and bool-vector elements must be t
or nil. Char-tables are like vectors except that they are
indexed by any valid character code. The characters in a string can
have text properties like characters in a buffer (see Text Properties), but vectors do not support text properties, even when
their elements happen to be characters.
Lists, strings and the other array types are different, but they have
important similarities. For example, all have a length l, and all
have elements which can be indexed from zero to l minus one.
Several functions, called sequence functions, accept any kind of
sequence. For example, the function elt can be used to extract
an element of a sequence, given its index. See Sequences Arrays Vectors.
It is generally impossible to read the same sequence twice, since
sequences are always created anew upon reading. If you read the read
syntax for a sequence twice, you get two sequences with equal contents.
There is one exception: the empty list () always stands for the
same object, nil.
A cons cell is an object that consists of two slots, called the car slot and the cdr slot. Each slot can hold or refer to any Lisp object. We also say that “the car of this cons cell is” whatever object its car slot currently holds, and likewise for the cdr.
A note to C programmers: in Lisp, we do not distinguish between “holding” a value and “pointing to” the value, because pointers in Lisp are implicit.
A list is a series of cons cells, linked together so that the cdr slot of each cons cell holds either the next cons cell or the empty list. See Lists, for functions that work on lists. Because most cons cells are used as part of lists, the phrase list structure has come to refer to any structure made out of cons cells.
The names car and cdr derive from the history of Lisp. The
original Lisp implementation ran on an IBM 704 computer which
divided words into two parts, called the “address” part and the
“decrement”; car was an instruction to extract the contents of
the address part of a register, and cdr an instruction to extract
the contents of the decrement. By contrast, “cons cells” are named
for the function cons that creates them, which in turn was named
for its purpose, the construction of cells.
Because cons cells are so central to Lisp, we also have a word for “an object which is not a cons cell”. These objects are called atoms.
The read syntax and printed representation for lists are identical, and consist of a left parenthesis, an arbitrary number of elements, and a right parenthesis.
Upon reading, each object inside the parentheses becomes an element
of the list. That is, a cons cell is made for each element. The
car slot of the cons cell holds the element, and its cdr
slot refers to the next cons cell of the list, which holds the next
element in the list. The cdr slot of the last cons cell is set to
hold nil.
A list can be illustrated by a diagram in which the cons cells are
shown as pairs of boxes, like dominoes. (The Lisp reader cannot read
such an illustration; unlike the textual notation, which can be
understood by both humans and computers, the box illustrations can be
understood only by humans.) This picture represents the three-element
list (rose violet buttercup):
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
--> rose --> violet --> buttercup
In this diagram, each box represents a slot that can hold or refer to any Lisp object. Each pair of boxes represents a cons cell. Each arrow represents a reference to a Lisp object, either an atom or another cons cell.
In this example, the first box, which holds the car of the first
cons cell, refers to or “holds” rose (a symbol). The second
box, holding the cdr of the first cons cell, refers to the next
pair of boxes, the second cons cell. The car of the second cons
cell is violet, and its cdr is the third cons cell. The
cdr of the third (and last) cons cell is nil.
Here is another diagram of the same list, (rose violet
buttercup), sketched in a different manner:
--------------- ---------------- -------------------
| car | cdr | | car | cdr | | car | cdr |
| rose | o-------->| violet | o-------->| buttercup | nil |
| | | | | | | | |
--------------- ---------------- -------------------
A list with no elements in it is the empty list; it is identical
to the symbol nil. In other words, nil is both a symbol
and a list.
Here are examples of lists written in Lisp syntax:
(A 2 "A") ; A list of three elements. () ; A list of no elements (the empty list). nil ; A list of no elements (the empty list). ("A ()") ; A list of one element: the string"A ()". (A ()) ; A list of two elements:Aand the empty list. (A nil) ; Equivalent to the previous. ((A B C)) ; A list of one element ; (which is a list of three elements).
Here is the list (A ()), or equivalently (A nil),
depicted with boxes and arrows:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> A --> nil
Dotted pair notation is an alternative syntax for cons cells
that represents the car and cdr explicitly. In this syntax,
(a . b) stands for a cons cell whose car is
the object a, and whose cdr is the object b. Dotted
pair notation is therefore more general than list syntax. In the dotted
pair notation, the list ‘(1 2 3)’ is written as ‘(1 . (2 . (3
. nil)))’. For nil-terminated lists, you can use either
notation, but list notation is usually clearer and more convenient.
When printing a list, the dotted pair notation is only used if the
cdr of a cons cell is not a list.
Here's an example using boxes to illustrate dotted pair notation.
This example shows the pair (rose . violet):
--- ---
| | |--> violet
--- ---
|
|
--> rose
You can combine dotted pair notation with list notation to represent
conveniently a chain of cons cells with a non-nil final cdr.
You write a dot after the last element of the list, followed by the
cdr of the final cons cell. For example, (rose violet
. buttercup) is equivalent to (rose . (violet . buttercup)).
The object looks like this:
--- --- --- ---
| | |--> | | |--> buttercup
--- --- --- ---
| |
| |
--> rose --> violet
The syntax (rose . violet . buttercup) is invalid because
there is nothing that it could mean. If anything, it would say to put
buttercup in the cdr of a cons cell whose cdr is already
used for violet.
The list (rose violet) is equivalent to (rose . (violet)),
and looks like this:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> rose --> violet
Similarly, the three-element list (rose violet buttercup)
is equivalent to (rose . (violet . (buttercup))).
It looks like this:
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
--> rose --> violet --> buttercup
An association list or alist is a specially-constructed list whose elements are cons cells. In each element, the car is considered a key, and the cdr is considered an associated value. (In some cases, the associated value is stored in the car of the cdr.) Association lists are often used as stacks, since it is easy to add or remove associations at the front of the list.
For example,
(setq alist-of-colors
'((rose . red) (lily . white) (buttercup . yellow)))
sets the variable alist-of-colors to an alist of three elements. In the
first element, rose is the key and red is the value.
See Association Lists, for a further explanation of alists and for functions that work on alists. See Hash Tables, for another kind of lookup table, which is much faster for handling a large number of keys.
An array is composed of an arbitrary number of slots for holding or referring to other Lisp objects, arranged in a contiguous block of memory. Accessing any element of an array takes approximately the same amount of time. In contrast, accessing an element of a list requires time proportional to the position of the element in the list. (Elements at the end of a list take longer to access than elements at the beginning of a list.)
Emacs defines four types of array: strings, vectors, bool-vectors, and char-tables.
A string is an array of characters and a vector is an array of
arbitrary objects. A bool-vector can hold only t or nil.
These kinds of array may have any length up to the largest integer.
Char-tables are sparse arrays indexed by any valid character code; they
can hold arbitrary objects.
The first element of an array has index zero, the second element has index 1, and so on. This is called zero-origin indexing. For example, an array of four elements has indices 0, 1, 2, and 3. The largest possible index value is one less than the length of the array. Once an array is created, its length is fixed.
All Emacs Lisp arrays are one-dimensional. (Most other programming languages support multidimensional arrays, but they are not essential; you can get the same effect with an array of arrays.) Each type of array has its own read syntax; see the following sections for details.
The array type is contained in the sequence type and contains the string type, the vector type, the bool-vector type, and the char-table type.
A string is an array of characters. Strings are used for many purposes in Emacs, as can be expected in a text editor; for example, as the names of Lisp symbols, as messages for the user, and to represent text extracted from buffers. Strings in Lisp are constants: evaluation of a string returns the same string.
See Strings and Characters, for functions that operate on strings.
The read syntax for strings is a double-quote, an arbitrary number of
characters, and another double-quote, "like this". To include a
double-quote in a string, precede it with a backslash; thus, "\""
is a string containing just a single double-quote character. Likewise,
you can include a backslash by preceding it with another backslash, like
this: "this \\ is a single embedded backslash".
The newline character is not special in the read syntax for strings; if you write a new line between the double-quotes, it becomes a character in the string. But an escaped newline—one that is preceded by ‘\’—does not become part of the string; i.e., the Lisp reader ignores an escaped newline while reading a string. An escaped space ‘\ ’ is likewise ignored.
"It is useful to include newlines
in documentation strings,
but the newline is \
ignored if escaped."
=> "It is useful to include newlines
in documentation strings,
but the newline is ignored if escaped."
You can include a non-ascii international character in a string constant by writing it literally. There are two text representations for non-ascii characters in Emacs strings (and in buffers): unibyte and multibyte. If the string constant is read from a multibyte source, such as a multibyte buffer or string, or a file that would be visited as multibyte, then the character is read as a multibyte character, and that makes the string multibyte. If the string constant is read from a unibyte source, then the character is read as unibyte and that makes the string unibyte.
You can also represent a multibyte non-ascii character with its character code: use a hex escape, ‘\xnnnnnnn’, with as many digits as necessary. (Multibyte non-ascii character codes are all greater than 256.) Any character which is not a valid hex digit terminates this construct. If the next character in the string could be interpreted as a hex digit, write ‘\ ’ (backslash and space) to terminate the hex escape—for example, ‘\x8e0\ ’ represents one character, ‘a’ with grave accent. ‘\ ’ in a string constant is just like backslash-newline; it does not contribute any character to the string, but it does terminate the preceding hex escape.
Using a multibyte hex escape forces the string to multibyte. You can represent a unibyte non-ascii character with its character code, which must be in the range from 128 (0200 octal) to 255 (0377 octal). This forces a unibyte string.
See Text Representations, for more information about the two text representations.
You can use the same backslash escape-sequences in a string constant
as in character literals (but do not use the question mark that begins a
character constant). For example, you can write a string containing the
nonprinting characters tab and C-a, with commas and spaces between
them, like this: "\t, \C-a". See Character Type, for a
description of the read syntax for characters.
However, not all of the characters you can write with backslash escape-sequences are valid in strings. The only control characters that a string can hold are the ascii control characters. Strings do not distinguish case in ascii control characters.
Properly speaking, strings cannot hold meta characters; but when a
string is to be used as a key sequence, there is a special convention
that provides a way to represent meta versions of ascii characters in a
string. If you use the ‘\M-’ syntax to indicate a meta character
in a string constant, this sets the
2**7
bit of the character in the string. If the string is used in
define-key or lookup-key, this numeric code is translated
into the equivalent meta character. See Character Type.
Strings cannot hold characters that have the hyper, super, or alt modifiers.
A string can hold properties for the characters it contains, in addition to the characters themselves. This enables programs that copy text between strings and buffers to copy the text's properties with no special effort. See Text Properties, for an explanation of what text properties mean. Strings with text properties use a special read and print syntax:
#("characters" property-data...)
where property-data consists of zero or more elements, in groups of three as follows:
beg end plist
The elements beg and end are integers, and together specify a range of indices in the string; plist is the property list for that range. For example,
#("foo bar" 0 3 (face bold) 3 4 nil 4 7 (face italic))
represents a string whose textual contents are ‘foo bar’, in which
the first three characters have a face property with value
bold, and the last three have a face property with value
italic. (The fourth character has no text properties, so its
property list is nil. It is not actually necessary to mention
ranges with nil as the property list, since any characters not
mentioned in any range will default to having no properties.)
A vector is a one-dimensional array of elements of any type. It takes a constant amount of time to access any element of a vector. (In a list, the access time of an element is proportional to the distance of the element from the beginning of the list.)
The printed representation of a vector consists of a left square bracket, the elements, and a right square bracket. This is also the read syntax. Like numbers and strings, vectors are considered constants for evaluation.
[1 "two" (three)] ; A vector of three elements.
=> [1 "two" (three)]
See Vectors, for functions that work with vectors.
A char-table is a one-dimensional array of elements of any type, indexed by character codes. Char-tables have certain extra features to make them more useful for many jobs that involve assigning information to character codes—for example, a char-table can have a parent to inherit from, a default value, and a small number of extra slots to use for special purposes. A char-table can also specify a single value for a whole character set.
The printed representation of a char-table is like a vector except that there is an extra ‘#^’ at the beginning.
See Char-Tables, for special functions to operate on char-tables. Uses of char-tables include:
A bool-vector is a one-dimensional array of elements that
must be t or nil.
The printed representation of a bool-vector is like a string, except
that it begins with ‘#&’ followed by the length. The string
constant that follows actually specifies the contents of the bool-vector
as a bitmap—each “character” in the string contains 8 bits, which
specify the next 8 elements of the bool-vector (1 stands for t,
and 0 for nil). The least significant bits of the character
correspond to the lowest indices in the bool-vector. If the length is not a
multiple of 8, the printed representation shows extra elements, but
these extras really make no difference.
(make-bool-vector 3 t)
=> #&3"\007"
(make-bool-vector 3 nil)
=> #&3"\0"
;; These are equal since only the first 3 bits are used.
(equal #&3"\377" #&3"\007")
=> t
A hash table is a very fast kind of lookup table, somewhat like an alist in that it maps keys to corresponding values, but much faster. Hash tables are a new feature in Emacs 21; they have no read syntax, and print using hash notation. See Hash Tables.
(make-hash-table)
=> #<hash-table 'eql nil 0/65 0x83af980>
Just as functions in other programming languages are executable,
Lisp function objects are pieces of executable code. However,
functions in Lisp are primarily Lisp objects, and only secondarily the
text which represents them. These Lisp objects are lambda expressions:
lists whose first element is the symbol lambda (see Lambda Expressions).
In most programming languages, it is impossible to have a function without a name. In Lisp, a function has no intrinsic name. A lambda expression is also called an anonymous function (see Anonymous Functions). A named function in Lisp is actually a symbol with a valid function in its function cell (see Defining Functions).
Most of the time, functions are called when their names are written in
Lisp expressions in Lisp programs. However, you can construct or obtain
a function object at run time and then call it with the primitive
functions funcall and apply. See Calling Functions.
A Lisp macro is a user-defined construct that extends the Lisp
language. It is represented as an object much like a function, but with
different argument-passing semantics. A Lisp macro has the form of a
list whose first element is the symbol macro and whose cdr
is a Lisp function object, including the lambda symbol.
Lisp macro objects are usually defined with the built-in
defmacro function, but any list that begins with macro is
a macro as far as Emacs is concerned. See Macros, for an explanation
of how to write a macro.
Warning: Lisp macros and keyboard macros (see Keyboard Macros) are entirely different things. When we use the word “macro” without qualification, we mean a Lisp macro, not a keyboard macro.
A primitive function is a function callable from Lisp but written in the C programming language. Primitive functions are also called subrs or built-in functions. (The word “subr” is derived from “subroutine”.) Most primitive functions evaluate all their arguments when they are called. A primitive function that does not evaluate all its arguments is called a special form (see Special Forms).
It does not matter to the caller of a function whether the function is primitive. However, this does matter if you try to redefine a primitive with a function written in Lisp. The reason is that the primitive function may be called directly from C code. Calls to the redefined function from Lisp will use the new definition, but calls from C code may still use the built-in definition. Therefore, we discourage redefinition of primitive functions.
The term function refers to all Emacs functions, whether written in Lisp or C. See Function Type, for information about the functions written in Lisp.
Primitive functions have no read syntax and print in hash notation with the name of the subroutine.
(symbol-function 'car) ; Access the function cell ; of the symbol. => #<subr car> (subrp (symbol-function 'car)) ; Is this a primitive function? => t ; Yes.
The byte compiler produces byte-code function objects. Internally, a byte-code function object is much like a vector; however, the evaluator handles this data type specially when it appears as a function to be called. See Byte Compilation, for information about the byte compiler.
The printed representation and read syntax for a byte-code function object is like that for a vector, with an additional ‘#’ before the opening ‘[’.
An autoload object is a list whose first element is the symbol
autoload. It is stored as the function definition of a symbol,
where it serves as a placeholder for the real definition. The autoload
object says that the real definition is found in a file of Lisp code
that should be loaded when necessary. It contains the name of the file,
plus some other information about the real definition.
After the file has been loaded, the symbol should have a new function definition that is not an autoload object. The new definition is then called as if it had been there to begin with. From the user's point of view, the function call works as expected, using the function definition in the loaded file.
An autoload object is usually created with the function
autoload, which stores the object in the function cell of a
symbol. See Autoload, for more details.
The types in the previous section are used for general programming purposes, and most of them are common to most Lisp dialects. Emacs Lisp provides several additional data types for purposes connected with editing.
A buffer is an object that holds text that can be edited (see Buffers). Most buffers hold the contents of a disk file (see Files) so they can be edited, but some are used for other purposes. Most buffers are also meant to be seen by the user, and therefore displayed, at some time, in a window (see Windows). But a buffer need not be displayed in any window.
The contents of a buffer are much like a string, but buffers are not used like strings in Emacs Lisp, and the available operations are different. For example, you can insert text efficiently into an existing buffer, altering the buffer's contents, whereas “inserting” text into a string requires concatenating substrings, and the result is an entirely new string object.
Each buffer has a designated position called point (see Positions). At any time, one buffer is the current buffer. Most editing commands act on the contents of the current buffer in the neighborhood of point. Many of the standard Emacs functions manipulate or test the characters in the current buffer; a whole chapter in this manual is devoted to describing these functions (see Text).
Several other data structures are associated with each buffer:
The local keymap and variable list contain entries that individually override global bindings or values. These are used to customize the behavior of programs in different buffers, without actually changing the programs.
A buffer may be indirect, which means it shares the text of another buffer, but presents it differently. See Indirect Buffers.
Buffers have no read syntax. They print in hash notation, showing the buffer name.
(current-buffer)
=> #<buffer objects.texi>
A marker denotes a position in a specific buffer. Markers therefore have two components: one for the buffer, and one for the position. Changes in the buffer's text automatically relocate the position value as necessary to ensure that the marker always points between the same two characters in the buffer.
Markers have no read syntax. They print in hash notation, giving the current character position and the name of the buffer.
(point-marker)
=> #<marker at 10779 in objects.texi>
See Markers, for information on how to test, create, copy, and move markers.
A window describes the portion of the terminal screen that Emacs uses to display a buffer. Every window has one associated buffer, whose contents appear in the window. By contrast, a given buffer may appear in one window, no window, or several windows.
Though many windows may exist simultaneously, at any time one window is designated the selected window. This is the window where the cursor is (usually) displayed when Emacs is ready for a command. The selected window usually displays the current buffer, but this is not necessarily the case.
Windows are grouped on the screen into frames; each window belongs to one and only one frame. See Frame Type.
Windows have no read syntax. They print in hash notation, giving the window number and the name of the buffer being displayed. The window numbers exist to identify windows uniquely, since the buffer displayed in any given window can change frequently.
(selected-window)
=> #<window 1 on objects.texi>
See Windows, for a description of the functions that work on windows.
A frame is a rectangle on the screen that contains one or more Emacs windows. A frame initially contains a single main window (plus perhaps a minibuffer window) which you can subdivide vertically or horizontally into smaller windows.
Frames have no read syntax. They print in hash notation, giving the frame's title, plus its address in core (useful to identify the frame uniquely).
(selected-frame)
=> #<frame emacs@psilocin.gnu.org 0xdac80>
See Frames, for a description of the functions that work on frames.
A window configuration stores information about the positions, sizes, and contents of the windows in a frame, so you can recreate the same arrangement of windows later.
Window configurations do not have a read syntax; their print syntax looks like ‘#<window-configuration>’. See Window Configurations, for a description of several functions related to window configurations.
A frame configuration stores information about the positions,
sizes, and contents of the windows in all frames. It is actually
a list whose car is frame-configuration and whose
cdr is an alist. Each alist element describes one frame,
which appears as the car of that element.
See Frame Configurations, for a description of several functions related to frame configurations.
The word process usually means a running program. Emacs itself runs in a process of this sort. However, in Emacs Lisp, a process is a Lisp object that designates a subprocess created by the Emacs process. Programs such as shells, GDB, ftp, and compilers, running in subprocesses of Emacs, extend the capabilities of Emacs.
An Emacs subprocess takes textual input from Emacs and returns textual output to Emacs for further manipulation. Emacs can also send signals to the subprocess.
Process objects have no read syntax. They print in hash notation, giving the name of the process:
(process-list)
=> (#<process shell>)
See Processes, for information about functions that create, delete, return information about, send input or signals to, and receive output from processes.
A stream is an object that can be used as a source or sink for characters—either to supply characters for input or to accept them as output. Many different types can be used this way: markers, buffers, strings, and functions. Most often, input streams (character sources) obtain characters from the keyboard, a buffer, or a file, and output streams (character sinks) send characters to a buffer, such as a *Help* buffer, or to the echo area.
The object nil, in addition to its other meanings, may be used
as a stream. It stands for the value of the variable
standard-input or standard-output. Also, the object
t as a stream specifies input using the minibuffer
(see Minibuffers) or output in the echo area (see The Echo Area).
Streams have no special printed representation or read syntax, and print as whatever primitive type they are.
See Read and Print, for a description of functions related to streams, including parsing and printing functions.
A keymap maps keys typed by the user to commands. This mapping
controls how the user's command input is executed. A keymap is actually
a list whose car is the symbol keymap.
See Keymaps, for information about creating keymaps, handling prefix keys, local as well as global keymaps, and changing key bindings.
An overlay specifies properties that apply to a part of a buffer. Each overlay applies to a specified range of the buffer, and contains a property list (a list whose elements are alternating property names and values). Overlay properties are used to present parts of the buffer temporarily in a different display style. Overlays have no read syntax, and print in hash notation, giving the buffer name and range of positions.
See Overlays, for how to create and use overlays.
In Emacs 21, to represent shared or circular structure within a complex of Lisp objects, you can use the reader constructs ‘#n=’ and ‘#n#’.
Use #n= before an object to label it for later reference;
subsequently, you can use #n# to refer the same object in
another place. Here, n is some integer. For example, here is how
to make a list in which the first element recurs as the third element:
(#1=(a) b #1#)
This differs from ordinary syntax such as this
((a) b (a))
which would result in a list whose first and third elements look alike but are not the same Lisp object. This shows the difference:
(prog1 nil
(setq x '(#1=(a) b #1#)))
(eq (nth 0 x) (nth 2 x))
=> t
(setq x '((a) b (a)))
(eq (nth 0 x) (nth 2 x))
=> nil
You can also use the same syntax to make a circular structure, which appears as an “element” within itself. Here is an example:
#1=(a #1#)
This makes a list whose second element is the list itself. Here's how you can see that it really works:
(prog1 nil
(setq x '#1=(a #1#)))
(eq x (cadr x))
=> t
The Lisp printer can produce this syntax to record circular and shared
structure in a Lisp object, if you bind the variable print-circle
to a non-nil value. See Output Variables.
The Emacs Lisp interpreter itself does not perform type checking on the actual arguments passed to functions when they are called. It could not do so, since function arguments in Lisp do not have declared data types, as they do in other programming languages. It is therefore up to the individual function to test whether each actual argument belongs to a type that the function can use.
All built-in functions do check the types of their actual arguments
when appropriate, and signal a wrong-type-argument error if an
argument is of the wrong type. For example, here is what happens if you
pass an argument to + that it cannot handle:
(+ 2 'a)
error--> Wrong type argument: number-or-marker-p, a
If you want your program to handle different types differently, you must do explicit type checking. The most common way to check the type of an object is to call a type predicate function. Emacs has a type predicate for each type, as well as some predicates for combinations of types.
A type predicate function takes one argument; it returns t if
the argument belongs to the appropriate type, and nil otherwise.
Following a general Lisp convention for predicate functions, most type
predicates' names end with ‘p’.
Here is an example which uses the predicates listp to check for
a list and symbolp to check for a symbol.
(defun add-on (x)
(cond ((symbolp x)
;; If X is a symbol, put it on LIST.
(setq list (cons x list)))
((listp x)
;; If X is a list, add its elements to LIST.
(setq list (append x list)))
(t
;; We handle only symbols and lists.
(error "Invalid argument %s in add-on" x))))
Here is a table of predefined type predicates, in alphabetical order, with references to further information.
atomarraypbool-vector-pbufferpbyte-code-function-pcase-table-pchar-or-string-pchar-table-pcommandpconspdisplay-table-pfloatpframe-configuration-pframe-live-pframepfunctionpinteger-or-marker-pintegerpkeymappkeywordplistpmarkerpwholenumpnlistpnumberpnumber-or-marker-poverlaypprocesspsequencepstringpsubrpsymbolpsyntax-table-puser-variable-pvectorpwindow-configuration-pwindow-live-pwindowpThe most general way to check the type of an object is to call the
function type-of. Recall that each object belongs to one and
only one primitive type; type-of tells you which one (see Lisp Data Types). But type-of knows nothing about non-primitive
types. In most cases, it is more convenient to use type predicates than
type-of.
This function returns a symbol naming the primitive type of object. The value is one of the symbols
symbol,integer,float,string,cons,vector,char-table,bool-vector,hash-table,subr,compiled-function,marker,overlay,window,buffer,frame,process, orwindow-configuration.(type-of 1) => integer (type-of 'nil) => symbol (type-of '()) ;()isnil. => symbol (type-of '(x)) => cons
Here we describe two functions that test for equality between any two objects. Other functions test equality between objects of specific types, e.g., strings. For these predicates, see the appropriate chapter describing the data type.
This function returns
tif object1 and object2 are the same object,nilotherwise. The “same object” means that a change in one will be reflected by the same change in the other.
eqreturnstif object1 and object2 are integers with the same value. Also, since symbol names are normally unique, if the arguments are symbols with the same name, they areeq. For other types (e.g., lists, vectors, strings), two arguments with the same contents or elements are not necessarilyeqto each other: they areeqonly if they are the same object.(eq 'foo 'foo) => t (eq 456 456) => t (eq "asdf" "asdf") => nil (eq '(1 (2 (3))) '(1 (2 (3)))) => nil (setq foo '(1 (2 (3)))) => (1 (2 (3))) (eq foo foo) => t (eq foo '(1 (2 (3)))) => nil (eq [(1 2) 3] [(1 2) 3]) => nil (eq (point-marker) (point-marker)) => nilThe
make-symbolfunction returns an uninterned symbol, distinct from the symbol that is used if you write the name in a Lisp expression. Distinct symbols with the same name are noteq. See Creating Symbols.(eq (make-symbol "foo") 'foo) => nil
This function returns
tif object1 and object2 have equal components,nilotherwise. Whereaseqtests if its arguments are the same object,equallooks inside nonidentical arguments to see if their elements or contents are the same. So, if two objects areeq, they areequal, but the converse is not always true.(equal 'foo 'foo) => t (equal 456 456) => t (equal "asdf" "asdf") => t (eq "asdf" "asdf") => nil (equal '(1 (2 (3))) '(1 (2 (3)))) => t (eq '(1 (2 (3))) '(1 (2 (3)))) => nil (equal [(1 2) 3] [(1 2) 3]) => t (eq [(1 2) 3] [(1 2) 3]) => nil (equal (point-marker) (point-marker)) => t (eq (point-marker) (point-marker)) => nilComparison of strings is case-sensitive, but does not take account of text properties—it compares only the characters in the strings. A unibyte string never equals a multibyte string unless the contents are entirely ascii (see Text Representations).
(equal "asdf" "ASDF") => nilHowever, two distinct buffers are never considered
equal, even if their textual contents are the same.
The test for equality is implemented recursively; for example, given
two cons cells x and y, (equal x y)
returns t if and only if both the expressions below return
t:
(equal (car x) (car y))
(equal (cdr x) (cdr y))
Because of this recursive method, circular lists may therefore cause infinite recursion (leading to an error).
GNU Emacs supports two numeric data types: integers and floating point numbers. Integers are whole numbers such as −3, 0, 7, 13, and 511. Their values are exact. Floating point numbers are numbers with fractional parts, such as −4.5, 0.0, or 2.71828. They can also be expressed in exponential notation: 1.5e2 equals 150; in this example, ‘e2’ stands for ten to the second power, and that is multiplied by 1.5. Floating point values are not exact; they have a fixed, limited amount of precision.
The range of values for an integer depends on the machine. The minimum range is −134217728 to 134217727 (28 bits; i.e., -2**27 to 2**27 - 1), but some machines may provide a wider range. Many examples in this chapter assume an integer has 28 bits. The Lisp reader reads an integer as a sequence of digits with optional initial sign and optional final period.
1 ; The integer 1. 1. ; The integer 1. +1 ; Also the integer 1. -1 ; The integer −1. 268435457 ; Also the integer 1, due to overflow. 0 ; The integer 0. -0 ; The integer 0.
In addition, the Lisp reader recognizes a syntax for integers in bases other than 10: ‘#Binteger’ reads integer in binary (radix 2), ‘#Ointeger’ reads integer in octal (radix 8), ‘#Xinteger’ reads integer in hexadecimal (radix 16), and ‘#radixrinteger’ reads integer in radix radix (where radix is between 2 and 36, inclusivley). Case is not significant for the letter after ‘#’ (‘B’, ‘O’, etc.) that denotes the radix.
To understand how various functions work on integers, especially the bitwise operators (see Bitwise Operations), it is often helpful to view the numbers in their binary form.
In 28-bit binary, the decimal integer 5 looks like this:
0000 0000 0000 0000 0000 0000 0101
(We have inserted spaces between groups of 4 bits, and two spaces between groups of 8 bits, to make the binary integer easier to read.)
The integer −1 looks like this:
1111 1111 1111 1111 1111 1111 1111
−1 is represented as 28 ones. (This is called two's complement notation.)
The negative integer, −5, is creating by subtracting 4 from −1. In binary, the decimal integer 4 is 100. Consequently, −5 looks like this:
1111 1111 1111 1111 1111 1111 1011
In this implementation, the largest 28-bit binary integer value is 134,217,727 in decimal. In binary, it looks like this:
0111 1111 1111 1111 1111 1111 1111
Since the arithmetic functions do not check whether integers go outside their range, when you add 1 to 134,217,727, the value is the negative integer −134,217,728:
(+ 1 134217727)
=> -134217728
=> 1000 0000 0000 0000 0000 0000 0000
Many of the functions described in this chapter accept markers for arguments in place of numbers. (See Markers.) Since the actual arguments to such functions may be either numbers or markers, we often give these arguments the name number-or-marker. When the argument value is a marker, its position value is used and its buffer is ignored.
Floating point numbers are useful for representing numbers that are
not integral. The precise range of floating point numbers is
machine-specific; it is the same as the range of the C data type
double on the machine you are using.
The read-syntax for floating point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, ‘1500.0’, ‘15e2’, ‘15.0e2’, ‘1.5e3’, and ‘.15e4’ are five ways of writing a floating point number whose value is 1500. They are all equivalent. You can also use a minus sign to write negative floating point numbers, as in ‘-1.0’.
Most modern computers support the IEEE floating point standard, which
provides for positive infinity and negative infinity as floating point
values. It also provides for a class of values called NaN or
“not-a-number”; numerical functions return such values in cases where
there is no correct answer. For example, (sqrt -1.0) returns a
NaN. For practical purposes, there's no significant difference between
different NaN values in Emacs Lisp, and there's no rule for precisely
which NaN value should be used in a particular case, so Emacs Lisp
doesn't try to distinguish them. Here are the read syntaxes for
these special floating point values:
In addition, the value -0.0 is distinguishable from ordinary
zero in IEEE floating point (although equal and = consider
them equal values).
You can use logb to extract the binary exponent of a floating
point number (or estimate the logarithm of an integer):
This function returns the binary exponent of number. More precisely, the value is the logarithm of number base 2, rounded down to an integer.
(logb 10) => 3 (logb 10.0e20) => 69
The functions in this section test whether the argument is a number or
whether it is a certain sort of number. The functions integerp
and floatp can take any type of Lisp object as argument (the
predicates would not be of much use otherwise); but the zerop
predicate requires a number as its argument. See also
integer-or-marker-p and number-or-marker-p, in
Predicates on Markers.
This predicate tests whether its argument is a floating point number and returns
tif so,nilotherwise.
floatpdoes not exist in Emacs versions 18 and earlier.
This predicate tests whether its argument is an integer, and returns
tif so,nilotherwise.
This predicate tests whether its argument is a number (either integer or floating point), and returns
tif so,nilotherwise.
The
wholenumppredicate (whose name comes from the phrase “whole-number-p”) tests to see whether its argument is a nonnegative integer, and returnstif so,nilotherwise. 0 is considered non-negative.
This predicate tests whether its argument is zero, and returns
tif so,nilotherwise. The argument must be a number.These two forms are equivalent:
(zerop x)==(= x 0).
To test numbers for numerical equality, you should normally use
=, not eq. There can be many distinct floating point
number objects with the same numeric value. If you use eq to
compare them, then you test whether two values are the same
object. By contrast, = compares only the numeric values
of the objects.
At present, each integer value has a unique Lisp object in Emacs Lisp.
Therefore, eq is equivalent to = where integers are
concerned. It is sometimes convenient to use eq for comparing an
unknown value with an integer, because eq does not report an
error if the unknown value is not a number—it accepts arguments of any
type. By contrast, = signals an error if the arguments are not
numbers or markers. However, it is a good idea to use = if you
can, even for comparing integers, just in case we change the
representation of integers in a future Emacs version.
Sometimes it is useful to compare numbers with equal; it treats
two numbers as equal if they have the same data type (both integers, or
both floating point) and the same value. By contrast, = can
treat an integer and a floating point number as equal.
There is another wrinkle: because floating point arithmetic is not exact, it is often a bad idea to check for equality of two floating point values. Usually it is better to test for approximate equality. Here's a function to do this:
(defvar fuzz-factor 1.0e-6)
(defun approx-equal (x y)
(or (and (= x 0) (= y 0))
(< (/ (abs (- x y))
(max (abs x) (abs y)))
fuzz-factor)))
Common Lisp note: Comparing numbers in Common Lisp always requires
= because Common Lisp implements multi-word integers, and two
distinct integer objects can have the same numeric value. Emacs Lisp
can have just one integer object for any given value because it has a
limited range of integer values.
This function tests whether its arguments are numerically equal, and returns
tif so,nilotherwise.
This function tests whether its arguments are numerically equal, and returns
tif they are not, andnilif they are.
This function tests whether its first argument is strictly less than its second argument. It returns
tif so,nilotherwise.
This function tests whether its first argument is less than or equal to its second argument. It returns
tif so,nilotherwise.
This function tests whether its first argument is strictly greater than its second argument. It returns
tif so,nilotherwise.
This function tests whether its first argument is greater than or equal to its second argument. It returns
tif so,nilotherwise.
This function returns the largest of its arguments. If any of the argument is floating-point, the value is returned as floating point, even if it was given as an integer.
(max 20) => 20 (max 1 2.5) => 2.5 (max 1 3 2.5) => 3.0
This function returns the smallest of its arguments. If any of the argument is floating-point, the value is returned as floating point, even if it was given as an integer.
(min -4 1) => -4
To convert an integer to floating point, use the function float.
This returns number converted to floating point. If number is already a floating point number,
floatreturns it unchanged.
There are four functions to convert floating point numbers to integers; they differ in how they round. These functions accept integer arguments also, and return such arguments unchanged.
This returns number, converted to an integer by rounding towards zero.
(truncate 1.2) => 1 (truncate 1.7) => 1 (truncate -1.2) => -1 (truncate -1.7) => -1
This returns number, converted to an integer by rounding downward (towards negative infinity).
If divisor is specified,
floordivides number by divisor and then converts to an integer; this uses the kind of division operation that corresponds tomod, rounding downward. Anarith-errorresults if divisor is 0.(floor 1.2) => 1 (floor 1.7) => 1 (floor -1.2) => -2 (floor -1.7) => -2 (floor 5.99 3) => 1
This returns number, converted to an integer by rounding upward (towards positive infinity).
(ceiling 1.2) => 2 (ceiling 1.7) => 2 (ceiling -1.2) => -1 (ceiling -1.7) => -1
This returns number, converted to an integer by rounding towards the nearest integer. Rounding a value equidistant between two integers may choose the integer closer to zero, or it may prefer an even integer, depending on your machine.
(round 1.2) => 1 (round 1.7) => 2 (round -1.2) => -1 (round -1.7) => -2
Emacs Lisp provides the traditional four arithmetic operations: addition, subtraction, multiplication, and division. Remainder and modulus functions supplement the division functions. The functions to add or subtract 1 are provided because they are traditional in Lisp and commonly used.
All of these functions except % return a floating point value
if any argument is floating.
It is important to note that in Emacs Lisp, arithmetic functions
do not check for overflow. Thus (1+ 134217727) may evaluate to
−134217728, depending on your hardware.
This function returns number-or-marker plus 1. For example,
(setq foo 4) => 4 (1+ foo) => 5This function is not analogous to the C operator
++—it does not increment a variable. It just computes a sum. Thus, if we continue,foo => 4If you want to increment the variable, you must use
setq, like this:(setq foo (1+ foo)) => 5
This function adds its arguments together. When given no arguments,
+returns 0.(+) => 0 (+ 1) => 1 (+ 1 2 3 4) => 10
The
-function serves two purposes: negation and subtraction. When-has a single argument, the value is the negative of the argument. When there are multiple arguments,-subtracts each of the more-numbers-or-markers from number-or-marker, cumulatively. If there are no arguments, the result is 0.(- 10 1 2 3 4) => 0 (- 10) => -10 (-) => 0
This function multiplies its arguments together, and returns the product. When given no arguments,
*returns 1.(*) => 1 (* 1) => 1 (* 1 2 3 4) => 24
This function divides dividend by divisor and returns the quotient. If there are additional arguments divisors, then it divides dividend by each divisor in turn. Each argument may be a number or a marker.
If all the arguments are integers, then the result is an integer too. This means the result has to be rounded. On most machines, the result is rounded towards zero after each division, but some machines may round differently with negative arguments. This is because the Lisp function
/is implemented using the C division operator, which also permits machine-dependent rounding. As a practical matter, all known machines round in the standard fashion.If you divide an integer by 0, an
arith-errorerror is signaled. (See Errors.) Floating point division by zero returns either infinity or a NaN if your machine supports IEEE floating point; otherwise, it signals anarith-errorerror.(/ 6 2) => 3 (/ 5 2) => 2 (/ 5.0 2) => 2.5 (/ 5 2.0) => 2.5 (/ 5.0 2.0) => 2.5 (/ 25 3 2) => 4 (/ -17 6) => -2The result of
(/ -17 6)could in principle be -3 on some machines.
This function returns the integer remainder after division of dividend by divisor. The arguments must be integers or markers.
For negative arguments, the remainder is in principle machine-dependent since the quotient is; but in practice, all known machines behave alike.
An
arith-errorresults if divisor is 0.(% 9 4) => 1 (% -9 4) => -1 (% 9 -4) => 1 (% -9 -4) => -1For any two integers dividend and divisor,
(+ (% dividend divisor) (* (/ dividend divisor) divisor))always equals dividend.
This function returns the value of dividend modulo divisor; in other words, the remainder after division of dividend by divisor, but with the same sign as divisor. The arguments must be numbers or markers.
Unlike
%,modreturns a well-defined result for negative arguments. It also permits floating point arguments; it rounds the quotient downward (towards minus infinity) to an integer, and uses that quotient to compute the remainder.An
arith-errorresults if divisor is 0.(mod 9 4) => 1 (mod -9 4) => 3 (mod 9 -4) => -3 (mod -9 -4) => -1 (mod 5.5 2.5) => .5For any two numbers dividend and divisor,
(+ (mod dividend divisor) (* (floor dividend divisor) divisor))always equals dividend, subject to rounding error if either argument is floating point. For
floor, see Numeric Conversions.
The functions ffloor, fceiling, fround, and
ftruncate take a floating point argument and return a floating
point result whose value is a nearby integer. ffloor returns the
nearest integer below; fceiling, the nearest integer above;
ftruncate, the nearest integer in the direction towards zero;
fround, the nearest integer.
This function rounds float to the next lower integral value, and returns that value as a floating point number.
This function rounds float to the next higher integral value, and returns that value as a floating point number.
This function rounds float towards zero to an integral value, and returns that value as a floating point number.
This function rounds float to the nearest integral value, and returns that value as a floating point number.
In a computer, an integer is represented as a binary number, a sequence of bits (digits which are either zero or one). A bitwise operation acts on the individual bits of such a sequence. For example, shifting moves the whole sequence left or right one or more places, reproducing the same pattern “moved over”.
The bitwise operations in Emacs Lisp apply only to integers.
lsh, which is an abbreviation for logical shift, shifts the bits in integer1 to the left count places, or to the right if count is negative, bringing zeros into the vacated bits. If count is negative,lshshifts zeros into the leftmost (most-significant) bit, producing a positive result even if integer1 is negative. Contrast this withash, below.Here are two examples of
lsh, shifting a pattern of bits one place to the left. We show only the low-order eight bits of the binary pattern; the rest are all zero.(lsh 5 1) => 10 ;; Decimal 5 becomes decimal 10. 00000101 => 00001010 (lsh 7 1) => 14 ;; Decimal 7 becomes decimal 14. 00000111 => 00001110As the examples illustrate, shifting the pattern of bits one place to the left produces a number that is twice the value of the previous number.
Shifting a pattern of bits two places to the left produces results like this (with 8-bit binary numbers):
(lsh 3 2) => 12 ;; Decimal 3 becomes decimal 12. 00000011 => 00001100On the other hand, shifting one place to the right looks like this:
(lsh 6 -1) => 3 ;; Decimal 6 becomes decimal 3. 00000110 => 00000011 (lsh 5 -1) => 2 ;; Decimal 5 becomes decimal 2. 00000101 => 00000010As the example illustrates, shifting one place to the right divides the value of a positive integer by two, rounding downward.
The function
lsh, like all Emacs Lisp arithmetic functions, does not check for overflow, so shifting left can discard significant bits and change the sign of the number. For example, left shifting 134,217,727 produces −2 on a 28-bit machine:(lsh 134217727 1) ; left shift => -2In binary, in the 28-bit implementation, the argument looks like this:
;; Decimal 134,217,727 0111 1111 1111 1111 1111 1111 1111which becomes the following when left shifted:
;; Decimal −2 1111 1111 1111 1111 1111 1111 1110
ash(arithmetic shift) shifts the bits in integer1 to the left count places, or to the right if count is negative.
ashgives the same results aslshexcept when integer1 and count are both negative. In that case,ashputs ones in the empty bit positions on the left, whilelshputs zeros in those bit positions.Thus, with
ash, shifting the pattern of bits one place to the right looks like this:(ash -6 -1) => -3 ;; Decimal −6 becomes decimal −3. 1111 1111 1111 1111 1111 1111 1010 => 1111 1111 1111 1111 1111 1111 1101In contrast, shifting the pattern of bits one place to the right with
lshlooks like this:(lsh -6 -1) => 134217725 ;; Decimal −6 becomes decimal 134,217,725. 1111 1111 1111 1111 1111 1111 1010 => 0111 1111 1111 1111 1111 1111 1101Here are other examples:
; 28-bit binary values (lsh 5 2) ; 5 = 0000 0000 0000 0000 0000 0000 0101 => 20 ; = 0000 0000 0000 0000 0000 0001 0100 (ash 5 2) => 20 (lsh -5 2) ; -5 = 1111 1111 1111 1111 1111 1111 1011 => -20 ; = 1111 1111 1111 1111 1111 1110 1100 (ash -5 2) => -20 (lsh 5 -2) ; 5 = 0000 0000 0000 0000 0000 0000 0101 => 1 ; = 0000 0000 0000 0000 0000 0000 0001 (ash 5 -2) => 1 (lsh -5 -2) ; -5 = 1111 1111 1111 1111 1111 1111 1011 => 4194302 ; = 0011 1111 1111 1111 1111 1111 1110 (ash -5 -2) ; -5 = 1111 1111 1111 1111 1111 1111 1011 => -2 ; = 1111 1111 1111 1111 1111 1111 1110
This function returns the “logical and” of the arguments: the nth bit is set in the result if, and only if, the nth bit is set in all the arguments. (“Set” means that the value of the bit is 1 rather than 0.)
For example, using 4-bit binary numbers, the “logical and” of 13 and 12 is 12: 1101 combined with 1100 produces 1100. In both the binary numbers, the leftmost two bits are set (i.e., they are 1's), so the leftmost two bits of the returned value are set. However, for the rightmost two bits, each is zero in at least one of the arguments, so the rightmost two bits of the returned value are 0's.
Therefore,
(logand 13 12) => 12If
logandis not passed any argument, it returns a value of −1. This number is an identity element forlogandbecause its binary representation consists entirely of ones. Iflogandis passed just one argument, it returns that argument.; 28-bit binary values (logand 14 13) ; 14 = 0000 0000 0000 0000 0000 0000 1110 ; 13 = 0000 0000 0000 0000 0000 0000 1101 => 12 ; 12 = 0000 0000 0000 0000 0000 0000 1100 (logand 14 13 4) ; 14 = 0000 0000 0000 0000 0000 0000 1110 ; 13 = 0000 0000 0000 0000 0000 0000 1101 ; 4 = 0000 0000 0000 0000 0000 0000 0100 => 4 ; 4 = 0000 0000 0000 0000 0000 0000 0100 (logand) => -1 ; -1 = 1111 1111 1111 1111 1111 1111 1111
This function returns the “inclusive or” of its arguments: the nth bit is set in the result if, and only if, the nth bit is set in at least one of the arguments. If there are no arguments, the result is zero, which is an identity element for this operation. If
logioris passed just one argument, it returns that argument.; 28-bit binary values (logior 12 5) ; 12 = 0000 0000 0000 0000 0000 0000 1100 ; 5 = 0000 0000 0000 0000 0000 0000 0101 => 13 ; 13 = 0000 0000 0000 0000 0000 0000 1101 (logior 12 5 7) ; 12 = 0000 0000 0000 0000 0000 0000 1100 ; 5 = 0000 0000 0000 0000 0000 0000 0101 ; 7 = 0000 0000 0000 0000 0000 0000 0111 => 15 ; 15 = 0000 0000 0000 0000 0000 0000 1111
This function returns the “exclusive or” of its arguments: the nth bit is set in the result if, and only if, the nth bit is set in an odd number of the arguments. If there are no arguments, the result is 0, which is an identity element for this operation. If
logxoris passed just one argument, it returns that argument.; 28-bit binary values (logxor 12 5) ; 12 = 0000 0000 0000 0000 0000 0000 1100 ; 5 = 0000 0000 0000 0000 0000 0000 0101 => 9 ; 9 = 0000 0000 0000 0000 0000 0000 1001 (logxor 12 5 7) ; 12 = 0000 0000 0000 0000 0000 0000 1100 ; 5 = 0000 0000 0000 0000 0000 0000 0101 ; 7 = 0000 0000 0000 0000 0000 0000 0111 => 14 ; 14 = 0000 0000 0000 0000 0000 0000 1110
This function returns the logical complement of its argument: the nth bit is one in the result if, and only if, the nth bit is zero in integer, and vice-versa.
(lognot 5) => -6 ;; 5 = 0000 0000 0000 0000 0000 0000 0101 ;; becomes ;; -6 = 1111 1111 1111 1111 1111 1111 1010
These mathematical functions allow integers as well as floating point numbers as arguments.
These are the ordinary trigonometric functions, with argument measured in radians.
The value of
(asinarg)is a number between −pi/2 and pi/2 (inclusive) whose sine is arg; if, however, arg is out of range (outside [-1, 1]), then the result is a NaN.
The value of
(acosarg)is a number between 0 and pi (inclusive) whose cosine is arg; if, however, arg is out of range (outside [-1, 1]), then the result is a NaN.
The value of
(atanarg)is a number between −pi/2 and pi/2 (exclusive) whose tangent is arg.
This is the exponential function; it returns e to the power arg. e is a fundamental mathematical constant also called the base of natural logarithms.
This function returns the logarithm of arg, with base base. If you don't specify base, the base e is used. If arg is negative, the result is a NaN.
This function returns the logarithm of arg, with base 10. If arg is negative, the result is a NaN.
(log10x)==(logx10), at least approximately.
This function returns x raised to power y. If both arguments are integers and y is positive, the result is an integer; in this case, it is truncated to fit the range of possible integer values.
A deterministic computer program cannot generate true random numbers. For most purposes, pseudo-random numbers suffice. A series of pseudo-random numbers is generated in a deterministic fashion. The numbers are not truly random, but they have certain properties that mimic a random series. For example, all possible values occur equally often in a pseudo-random series.
In Emacs, pseudo-random numbers are generated from a “seed” number.
Starting from any given seed, the random function always
generates the same sequence of numbers. Emacs always starts with the
same seed value, so the sequence of values of random is actually
the same in each Emacs run! For example, in one operating system, the
first call to (random) after you start Emacs always returns
-1457731, and the second one always returns -7692030. This
repeatability is helpful for debugging.
If you want random numbers that don't always come out the same, execute
(random t). This chooses a new seed based on the current time of
day and on Emacs's process id number.
This function returns a pseudo-random integer. Repeated calls return a series of pseudo-random integers.
If limit is a positive integer, the value is chosen to be nonnegative and less than limit.
If limit is
t, it means to choose a new seed based on the current time of day and on Emacs's process id number.On some machines, any integer representable in Lisp may be the result of
random. On other machines, the result can never be larger than a certain maximum or less than a certain (negative) minimum.
A string in Emacs Lisp is an array that contains an ordered sequence of characters. Strings are used as names of symbols, buffers, and files; to send messages to users; to hold text being copied between buffers; and for many other purposes. Because strings are so important, Emacs Lisp has many functions expressly for manipulating them. Emacs Lisp programs use strings more often than individual characters.
See Strings of Events, for special considerations for strings of keyboard character events.
Characters are represented in Emacs Lisp as integers; whether an integer is a character or not is determined only by how it is used. Thus, strings really contain integers.
The length of a string (like any array) is fixed, and cannot be altered once the string exists. Strings in Lisp are not terminated by a distinguished character code. (By contrast, strings in C are terminated by a character with ascii code 0.)
Since strings are arrays, and therefore sequences as well, you can
operate on them with the general array and sequence functions.
(See Sequences Arrays Vectors.) For example, you can access or
change individual characters in a string using the functions aref
and aset (see Array Functions).
There are two text representations for non-ascii characters in Emacs strings (and in buffers): unibyte and multibyte (see Text Representations). An ascii character always occupies one byte in a string; in fact, when a string is all ascii, there is no real difference between the unibyte and multibyte representations. For most Lisp programming, you don't need to be concerned with these two representations.
Sometimes key sequences are represented as strings. When a string is a key sequence, string elements in the range 128 to 255 represent meta characters (which are large integers) rather than character codes in the range 128 to 255.
Strings cannot hold characters that have the hyper, super or alt modifiers; they can hold ascii control characters, but no other control characters. They do not distinguish case in ascii control characters. If you want to store such characters in a sequence, such as a key sequence, you must use a vector instead of a string. See Character Type, for more information about the representation of meta and other modifiers for keyboard input characters.
Strings are useful for holding regular expressions. You can also
match regular expressions against strings (see Regexp Search). The
functions match-string (see Simple Match Data) and
replace-match (see Replacing Match) are useful for
decomposing and modifying strings based on regular expression matching.
Like a buffer, a string can contain text properties for the characters in it, as well as the characters themselves. See Text Properties. All the Lisp primitives that copy text from strings to buffers or other strings also copy the properties of the characters being copied.
See Text, for information about functions that display strings or copy them into buffers. See Character Type, and String Type, for information about the syntax of characters and strings. See Non-ASCII Characters, for functions to convert between text representations and to encode and decode character codes.
For more information about general sequence and array predicates, see Sequences Arrays Vectors, and Arrays.
This function returns
tif object is a string or a character (i.e., an integer),nilotherwise.
The following functions create strings, either from scratch, or by putting strings together, or by taking them apart.
This function returns a string made up of count repetitions of character. If count is negative, an error is signaled.
(make-string 5 ?x) => "xxxxx" (make-string 0 ?x) => ""Other functions to compare with this one include
char-to-string(see String Conversion),make-vector(see Vectors), andmake-list(see Building Lists).
This returns a string containing the characters characters.
(string ?a ?b ?c) => "abc"
This function returns a new string which consists of those characters from string in the range from (and including) the character at the index start up to (but excluding) the character at the index end. The first character is at index zero.
(substring "abcdefg" 0 3) => "abc"Here the index for ‘a’ is 0, the index for ‘b’ is 1, and the index for ‘c’ is 2. Thus, three letters, ‘abc’, are copied from the string
"abcdefg". The index 3 marks the character position up to which the substring is copied. The character whose index is 3 is actually the fourth character in the string.A negative number counts from the end of the string, so that −1 signifies the index of the last character of the string. For example:
(substring "abcdefg" -3 -1) => "ef"In this example, the index for ‘e’ is −3, the index for ‘f’ is −2, and the index for ‘g’ is −1. Therefore, ‘e’ and ‘f’ are included, and ‘g’ is excluded.
When
nilis used as an index, it stands for the length of the string. Thus,(substring "abcdefg" -3 nil) => "efg"Omitting the argument end is equivalent to specifying
nil. It follows that(substringstring0)returns a copy of all of string.(substring "abcdefg" 0) => "abcdefg"But we recommend
copy-sequencefor this purpose (see Sequence Functions).If the characters copied from string have text properties, the properties are copied into the new string also. See Text Properties.
substringalso accepts a vector for the first argument. For example:(substring [a b (c) "d"] 1 3) => [b (c)]A
wrong-type-argumenterror is signaled if either start or end is not an integer ornil. Anargs-out-of-rangeerror is signaled if start indicates a character following end, or if either integer is out of range for string.Contrast this function with
buffer-substring(see Buffer Contents), which returns a string containing a portion of the text in the current buffer. The beginning of a string is at index 0, but the beginning of a buffer is at index 1.
This function returns a new string consisting of the characters in the arguments passed to it (along with their text properties, if any). The arguments may be strings, lists of numbers, or vectors of numbers; they are not themselves changed. If
concatreceives no arguments, it returns an empty string.(concat "abc" "-def") => "abc-def" (concat "abc" (list 120 121) [122]) => "abcxyz" ;;nilis an empty sequence. (concat "abc" nil "-def") => "abc-def" (concat "The " "quick brown " "fox.") => "The quick brown fox." (concat) => ""The
concatfunction always constructs a new string that is noteqto any existing string.In Emacs versions before 21, when an argument was an integer (not a sequence of integers), it was converted to a string of digits making up the decimal printed representation of the integer. This obsolete usage no longer works. The proper way to convert an integer to its decimal printed form is with
format(see Formatting Strings) ornumber-to-string(see String Conversion).For information about other concatenation functions, see the description of
mapconcatin Mapping Functions,vconcatin Vectors, andappendin Building Lists.
This function splits string into substrings at matches for the regular expression separators. Each match for separators defines a splitting point; the substrings between the splitting points are made into a list, which is the value returned by
split-string. If separators isnil(or omitted), the default is"[ \f\t\n\r\v]+".For example,
(split-string "Soup is good food" "o") => ("S" "up is g" "" "d f" "" "d") (split-string "Soup is good food" "o+") => ("S" "up is g" "d f" "d")When there is a match adjacent to the beginning or end of the string, this does not cause a null string to appear at the beginning or end of the list:
(split-string "out to moo" "o+") => ("ut t" " m")Empty matches do count, when not adjacent to another match:
(split-string "Soup is good food" "o*") =>("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d") (split-string "Nice doggy!" "") =>("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
The most basic way to alter the contents of an existing string is with
aset (see Array Functions). (aset string
idx char) stores char into string at index
idx. Each character occupies one or more bytes, and if char
needs a different number of bytes from the character already present at
that index, aset signals an error.
A more powerful function is store-substring:
This function alters part of the contents of the string string, by storing obj starting at index idx. The argument obj may be either a character or a (smaller) string.
Since it is impossible to change the length of an existing string, it is an error if obj doesn't fit within string's actual length, or if any new character requires a different number of bytes from the character currently present at that point in string.
This function returns
tif the arguments represent the same character,nilotherwise. This function ignores differences in case ifcase-fold-searchis non-nil.(char-equal ?x ?x) => t (let ((case-fold-search nil)) (char-equal ?x ?X)) => nil
This function returns
tif the characters of the two strings match exactly. Case is always significant, regardless ofcase-fold-search.(string= "abc" "abc") => t (string= "abc" "ABC") => nil (string= "ab" "ABC") => nilThe function
string=ignores the text properties of the two strings. Whenequal(see Equality Predicates) compares two strings, it usesstring=.If the strings contain non-ascii characters, and one is unibyte while the other is multibyte, then they cannot be equal. See Text Representations.
This function compares two strings a character at a time. It scans both the strings at the same time to find the first pair of corresponding characters that do not match. If the lesser character of these two is the character from string1, then string1 is less, and this function returns
t. If the lesser character is the one from string2, then string1 is greater, and this function returnsnil. If the two strings match entirely, the value isnil.Pairs of characters are compared according to their character codes. Keep in mind that lower case letters have higher numeric values in the ascii character set than their upper case counterparts; digits and many punctuation characters have a lower numeric value than upper case letters. An ascii character is less than any non-ascii character; a unibyte non-ascii character is always less than any multibyte non-ascii character (see Text Representations).
(string< "abc" "abd") => t (string< "abd" "abc") => nil (string< "123" "abc") => tWhen the strings have different lengths, and they match up to the length of string1, then the result is
t. If they match up to the length of string2, the result isnil. A string of no characters is less than any other string.(string< "" "abc") => t (string< "ab" "abc") => t (string< "abc" "") => nil (string< "abc" "ab") => nil (string< "" "") => nil
This function compares the specified part of string1 with the specified part of string2. The specified part of string1 runs from index start1 up to index end1 (
nilmeans the end of the string). The specified part of string2 runs from index start2 up to index end2 (nilmeans the end of the string).The strings are both converted to multibyte for the comparison (see Text Representations) so that a unibyte string can be equal to a multibyte string. If ignore-case is non-
nil, then case is ignored, so that upper case letters can be equal to lower case letters.If the specified portions of the two strings match, the value is
t. Otherwise, the value is an integer which indicates how many leading characters agree, and which string is less. Its absolute value is one plus the number of characters that agree at the beginning of the two strings. The sign is negative if string1 (or its specified portion) is less.
This function works like
assoc, except that key must be a string, and comparison is done usingcompare-strings, ignoring case differences. See Association Lists.
This function works like
assoc, except that key must be a string, and comparison is done usingcompare-strings. Case differences are significant.
See also compare-buffer-substrings in Comparing Text, for
a way to compare text in buffers. The function string-match,
which matches a regular expression against a string, can be used
for a kind of string comparison; see Regexp Search.
This section describes functions for conversions between characters,
strings and integers. format and prin1-to-string
(see Output Functions) can also convert Lisp objects into strings.
read-from-string (see Input Functions) can “convert” a
string representation of a Lisp object into an object. The functions
string-make-multibyte and string-make-unibyte convert the
text representation of a string (see Converting Representations).
See Documentation, for functions that produce textual descriptions
of text characters and general input events
(single-key-description and text-char-description). These
functions are used primarily for making help messages.
This function returns a new string containing one character, character. This function is semi-obsolete because the function
stringis more general. See Creating Strings.
This function returns the first character in string. If the string is empty, the function returns 0. The value is also 0 when the first character of string is the null character, ascii code 0.
(string-to-char "ABC") => 65 (string-to-char "xyz") => 120 (string-to-char "") => 0 (string-to-char "\000") => 0This function may be eliminated in the future if it does not seem useful enough to retain.
This function returns a string consisting of the printed base-ten representation of number, which may be an integer or a floating point number. The returned value starts with a minus sign if the argument is negative.
(number-to-string 256) => "256" (number-to-string -23) => "-23" (number-to-string -23.5) => "-23.5"
int-to-stringis a semi-obsolete alias for this function.See also the function
formatin Formatting Strings.
This function returns the numeric value of the characters in string. If base is non-
nil, integers are converted in that base. If base isnil, then base ten is used. Floating point conversion always uses base ten; we have not implemented other radices for floating point numbers, because that would be much more work and does not seem useful. If string looks like an integer but its value is too large to fit into a Lisp integer,string-to-numberreturns a floating point result.The parsing skips spaces and tabs at the beginning of string, then reads as much of string as it can interpret as a number. (On some systems it ignores other whitespace at the beginning, not just spaces and tabs.) If the first character after the ignored whitespace is neither a digit, nor a plus or minus sign, nor the leading dot of a floating point number, this function returns 0.
(string-to-number "256") => 256 (string-to-number "25 is a perfect square.") => 25 (string-to-number "X256") => 0 (string-to-number "-4.5") => -4.5 (string-to-number "1e5") => 100000.0
Here are some other functions that can convert to or from a string:
concatconcat can convert a vector or a list into a string.
See Creating Strings.
vconcatvconcat can convert a string into a vector. See Vector Functions.
appendappend can convert a string into a list. See Building Lists.
Formatting means constructing a string by substitution of computed values at various places in a constant string. This constant string controls how the other values are printed, as well as where they appear; it is called a format string.
Formatting is often useful for computing messages to be displayed. In
fact, the functions message and error provide the same
formatting feature described here; they differ from format only
in how they use the result of formatting.
This function returns a new string that is made by copying string and then replacing any format specification in the copy with encodings of the corresponding objects. The arguments objects are the computed values to be formatted.
The characters in string, other than the format specifications, are copied directly into the output; starting in Emacs 21, if they have text properties, these are copied into the output also.
A format specification is a sequence of characters beginning with a
‘%’. Thus, if there is a ‘%d’ in string, the
format function replaces it with the printed representation of
one of the values to be formatted (one of the arguments objects).
For example:
(format "The value of fill-column is %d." fill-column)
=> "The value of fill-column is 72."
If string contains more than one format specification, the format specifications correspond to successive values from objects. Thus, the first format specification in string uses the first such value, the second format specification uses the second such value, and so on. Any extra format specifications (those for which there are no corresponding values) cause unpredictable behavior. Any extra values to be formatted are ignored.
Certain format specifications require values of particular types. If you supply a value that doesn't fit the requirements, an error is signaled.
Here is a table of valid format specifications:
princ, not
prin1—see Output Functions). Thus, strings are represented
by their contents alone, with no ‘"’ characters, and symbols appear
without ‘\’ characters.
Starting in Emacs 21, if the object is a string, its text properties are copied into the output. The text properties of the ‘%s’ itself are also copied, but those of the object take priority.
If there is no corresponding object, the empty string is used.
prin1—see Output Functions). Thus, strings are enclosed in ‘"’ characters, and
‘\’ characters appear where necessary before special characters.
If there is no corresponding object, the empty string is used.
(format "%% %d" 30) returns "% 30".
Any other format character results in an ‘Invalid format operation’ error.
Here are several examples:
(format "The name of this buffer is %s." (buffer-name))
=> "The name of this buffer is strings.texi."
(format "The buffer object prints as %s." (current-buffer))
=> "The buffer object prints as strings.texi."
(format "The octal value of %d is %o,
and the hex value is %x." 18 18 18)
=> "The octal value of 18 is 22,
and the hex value is 12."
All the specification characters allow an optional numeric prefix between the ‘%’ and the character. The optional numeric prefix defines the minimum width for the object. If the printed representation of the object contains fewer characters than this, then it is padded. The padding is on the left if the prefix is positive (or starts with zero) and on the right if the prefix is negative. The padding character is normally a space, but if the numeric prefix starts with a zero, zeros are used for padding. Here are some examples of padding:
(format "%06d is padded on the left with zeros" 123)
=> "000123 is padded on the left with zeros"
(format "%-6d is padded on the right" 123)
=> "123 is padded on the right"
format never truncates an object's printed representation, no
matter what width you specify. Thus, you can use a numeric prefix to
specify a minimum spacing between columns with no risk of losing
information.
In the following three examples, ‘%7s’ specifies a minimum width
of 7. In the first case, the string inserted in place of ‘%7s’ has
only 3 letters, so 4 blank spaces are inserted for padding. In the
second case, the string "specification" is 13 letters wide but is
not truncated. In the third case, the padding is on the right.
(format "The word `%7s' actually has %d letters in it."
"foo" (length "foo"))
=> "The word ` foo' actually has 3 letters in it."
(format "The word `%7s' actually has %d letters in it."
"specification" (length "specification"))
=> "The word `specification' actually has 13 letters in it."
(format "The word `%-7s' actually has %d letters in it."
"foo" (length "foo"))
=> "The word `foo ' actually has 3 letters in it."
The character case functions change the case of single characters or of the contents of strings. The functions normally convert only alphabetic characters (the letters ‘A’ through ‘Z’ and ‘a’ through ‘z’, as well as non-ascii letters); other characters are not altered. You can specify a different case conversion mapping by specifying a case table (see Case Tables).
These functions do not modify the strings that are passed to them as arguments.
The examples below use the characters ‘X’ and ‘x’ which have ascii codes 88 and 120 respectively.
This function converts a character or a string to lower case.
When the argument to
downcaseis a string, the function creates and returns a new string in which each letter in the argument that is upper case is converted to lower case. When the argument todowncaseis a character,downcasereturns the corresponding lower case character. This value is an integer. If the original character is lower case, or is not a letter, then the value equals the original character.(downcase "The cat in the hat") => "the cat in the hat" (downcase ?X) => 120
This function converts a character or a string to upper case.
When the argument to
upcaseis a string, the function creates and returns a new string in which each letter in the argument that is lower case is converted to upper case.When the argument to
upcaseis a character,upcasereturns the corresponding upper case character. This value is an integer. If the original character is upper case, or is not a letter, then the value returned equals the original character.(upcase "The cat in the hat") => "THE CAT IN THE HAT" (upcase ?x) => 88
This function capitalizes strings or characters. If string-or-char is a string, the function creates and returns a new string, whose contents are a copy of string-or-char in which each word has been capitalized. This means that the first character of each word is converted to upper case, and the rest are converted to lower case.
The definition of a word is any sequence of consecutive characters that are assigned to the word constituent syntax class in the current syntax table (see Syntax Class Table).
When the argument to
capitalizeis a character,capitalizehas the same result asupcase.(capitalize "The cat in the hat") => "The Cat In The Hat" (capitalize "THE 77TH-HATTED CAT") => "The 77th-Hatted Cat" (capitalize ?x) => 88
This function capitalizes the initials of the words in string, without altering any letters other than the initials. It returns a new string whose contents are a copy of string, in which each word has had its initial letter converted to upper case.
The definition of a word is any sequence of consecutive characters that are assigned to the word constituent syntax class in the current syntax table (see Syntax Class Table).
(upcase-initials "The CAT in the hAt") => "The CAT In The HAt"
See Text Comparison, for functions that compare strings; some of them ignore case differences, or can optionally ignore case differences.
You can customize case conversion by installing a special case table. A case table specifies the mapping between upper case and lower case letters. It affects both the case conversion functions for Lisp objects (see the previous section) and those that apply to text in the buffer (see Case Changes). Each buffer has a case table; there is also a standard case table which is used to initialize the case table of new buffers.
A case table is a char-table (see Char-Tables) whose subtype is
case-table. This char-table maps each character into the
corresponding lower case character. It has three extra slots, which
hold related tables:
In simple cases, all you need to specify is the mapping to lower-case; the three related tables will be calculated automatically from that one.
For some languages, upper and lower case letters are not in one-to-one correspondence. There may be two different lower case letters with the same upper case equivalent. In these cases, you need to specify the maps for both lower case and upper case.
The extra table canonicalize maps each character to a canonical equivalent; any two characters that are related by case-conversion have the same canonical equivalent character. For example, since ‘a’ and ‘A’ are related by case-conversion, they should have the same canonical equivalent character (which should be either ‘a’ for both of them, or ‘A’ for both of them).
The extra table equivalences is a map that cyclicly permutes each equivalence class (of characters with the same canonical equivalent). (For ordinary ascii, this would map ‘a’ into ‘A’ and ‘A’ into ‘a’, and likewise for each set of equivalent characters.)
When you construct a case table, you can provide nil for
canonicalize; then Emacs fills in this slot from the lower case
and upper case mappings. You can also provide nil for
equivalences; then Emacs fills in this slot from
canonicalize. In a case table that is actually in use, those
components are non-nil. Do not try to specify equivalences
without also specifying canonicalize.
Here are the functions for working with case tables:
This function makes table the standard case table, so that it will be used in any buffers created subsequently.
The following three functions are convenient subroutines for packages that define non-ascii character sets. They modify the specified case table case-table; they also modify the standard syntax table. See Syntax Tables. Normally you would use these functions to change the standard case table.
This function specifies a pair of corresponding letters, one upper case and one lower case.
This function makes characters l and r a matching pair of case-invariant delimiters.
This function makes char case-invariant, with syntax syntax.
This command displays a description of the contents of the current buffer's case table.
A list represents a sequence of zero or more elements (which may be any Lisp objects). The important difference between lists and vectors is that two or more lists can share part of their structure; in addition, you can insert or delete elements in a list without copying the whole list.
Lists in Lisp are not a primitive data type; they are built up from cons cells. A cons cell is a data object that represents an ordered pair. That is, it has two slots, and each slot holds, or refers to, some Lisp object. One slot is known as the car, and the other is known as the cdr. (These names are traditional; see Cons Cell Type.) cdr is pronounced “could-er.”
We say that “the car of this cons cell is” whatever object its car slot currently holds, and likewise for the cdr.
A list is a series of cons cells “chained together,” so that each
cell refers to the next one. There is one cons cell for each element of
the list. By convention, the cars of the cons cells hold the
elements of the list, and the cdrs are used to chain the list: the
cdr slot of each cons cell refers to the following cons cell. The
cdr of the last cons cell is nil. This asymmetry between
the car and the cdr is entirely a matter of convention; at the
level of cons cells, the car and cdr slots have the same
characteristics.
Because most cons cells are used as part of lists, the phrase list structure has come to mean any structure made out of cons cells.
The symbol nil is considered a list as well as a symbol; it is
the list with no elements. For convenience, the symbol nil is
considered to have nil as its cdr (and also as its
car).
The cdr of any nonempty list l is a list containing all the elements of l except the first.
A cons cell can be illustrated as a pair of boxes. The first box
represents the car and the second box represents the cdr.
Here is an illustration of the two-element list, (tulip lily),
made from two cons cells:
--------------- ---------------
| car | cdr | | car | cdr |
| tulip | o---------->| lily | nil |
| | | | | |
--------------- ---------------
Each pair of boxes represents a cons cell. Each box “refers to”,
“points to” or “holds” a Lisp object. (These terms are
synonymous.) The first box, which describes the car of the first
cons cell, contains the symbol tulip. The arrow from the
cdr box of the first cons cell to the second cons cell indicates
that the cdr of the first cons cell is the second cons cell.
The same list can be illustrated in a different sort of box notation like this:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> tulip --> lily
Here is a more complex illustration, showing the three-element list,
((pine needles) oak maple), the first element of which is a
two-element list:
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
| --> oak --> maple
|
| --- --- --- ---
--> | | |--> | | |--> nil
--- --- --- ---
| |
| |
--> pine --> needles
The same list represented in the first box notation looks like this:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| o | o------->| oak | o------->| maple | nil |
| | | | | | | | | |
-- | --------- -------------- --------------
|
|
| -------------- ----------------
| | car | cdr | | car | cdr |
------>| pine | o------->| needles | nil |
| | | | | |
-------------- ----------------
See Cons Cell Type, for the read and print syntax of cons cells and lists, and for more “box and arrow” illustrations of lists.
The following predicates test whether a Lisp object is an atom, is a
cons cell or is a list, or whether it is the distinguished object
nil. (Many of these predicates can be defined in terms of the
others, but they are used so often that it is worth having all of them.)
This function returns
tif object is a cons cell,nilotherwise.nilis not a cons cell, although it is a list.
This function returns
tif object is an atom,nilotherwise. All objects except cons cells are atoms. The symbolnilis an atom and is also a list; it is the only Lisp object that is both.(atom object) == (not (consp object))
This function returns
tif object is a cons cell ornil. Otherwise, it returnsnil.(listp '(1)) => t (listp '()) => t
This function is the opposite of
listp: it returnstif object is not a list. Otherwise, it returnsnil.(listp object) == (not (nlistp object))
This function returns
tif object isnil, and returnsnilotherwise. This function is identical tonot, but as a matter of clarity we usenullwhen object is considered a list andnotwhen it is considered a truth value (seenotin Combining Conditions).(null '(1)) => nil (null '()) => t
This function returns the value referred to by the first slot of the cons cell cons-cell. Expressed another way, this function returns the car of cons-cell.
As a special case, if cons-cell is
nil, thencaris defined to returnnil; therefore, any list is a valid argument forcar. An error is signaled if the argument is not a cons cell ornil.(car '(a b c)) => a (car '()) => nil
This function returns the value referred to by the second slot of the cons cell cons-cell. Expressed another way, this function returns the cdr of cons-cell.
As a special case, if cons-cell is
nil, thencdris defined to returnnil; therefore, any list is a valid argument forcdr. An error is signaled if the argument is not a cons cell ornil.(cdr '(a b c)) => (b c) (cdr '()) => nil
This function lets you take the car of a cons cell while avoiding errors for other data types. It returns the car of object if object is a cons cell,
nilotherwise. This is in contrast tocar, which signals an error if object is not a list.(car-safe object) == (let ((x object)) (if (consp x) (car x) nil))
This function lets you take the cdr of a cons cell while avoiding errors for other data types. It returns the cdr of object if object is a cons cell,
nilotherwise. This is in contrast tocdr, which signals an error if object is not a list.(cdr-safe object) == (let ((x object)) (if (consp x) (cdr x) nil))
This macro is a way of examining the car of a list, and taking it off the list, all at once. It is new in Emacs 21.
It operates on the list which is stored in the symbol listname. It removes this element from the list by setting listname to the cdr of its old value—but it also returns the car of that list, which is the element being removed.
x => (a b c) (pop x) => a x => (b c)
This function returns the nth element of list. Elements are numbered starting with zero, so the car of list is element number zero. If the length of list is n or less, the value is
nil.If n is negative,
nthreturns the first element of list.(nth 2 '(1 2 3 4)) => 3 (nth 10 '(1 2 3 4)) => nil (nth -3 '(1 2 3 4)) => 1 (nth n x) == (car (nthcdr n x))The function
eltis similar, but applies to any kind of sequence. For historical reasons, it takes its arguments in the opposite order. See Sequence Functions.
This function returns the nth cdr of list. In other words, it skips past the first n links of list and returns what follows.
If n is zero or negative,
nthcdrreturns all of list. If the length of list is n or less,nthcdrreturnsnil.(nthcdr 1 '(1 2 3 4)) => (2 3 4) (nthcdr 10 '(1 2 3 4)) => nil (nthcdr -3 '(1 2 3 4)) => (1 2 3 4)
This function returns the last link of list. The
carof this link is the list's last element. If list is null,nilis returned. If n is non-nil the n-th-to-last link is returned instead, or the whole list if n is bigger than list's length.
This function returns the length of list, with no risk of either an error or an infinite loop.
If list is not really a list,
safe-lengthreturns 0. If list is circular, it returns a finite value which is at least the number of distinct elements.
The most common way to compute the length of a list, when you are not
worried that it may be circular, is with length. See Sequence Functions.
This function returns the list x with the last element, or the last n elements, removed. If n is greater than zero it makes a copy of the list so as not to damage the original list. In general,
(append (butlastx n) (lastx n))will return a list equal to x.
This is a version of
butlastthat works by destructively modifying thecdrof the appropriate element, rather than making a copy of the list.
Many functions build lists, as lists reside at the very heart of Lisp.
cons is the fundamental list-building function; however, it is
interesting to note that list is used more times in the source
code for Emacs than cons.
This function is the fundamental function used to build new list structure. It creates a new cons cell, making object1 the car, and object2 the cdr. It then returns the new cons cell. The arguments object1 and object2 may be any Lisp objects, but most often object2 is a list.
(cons 1 '(2)) => (1 2) (cons 1 '()) => (1) (cons 1 2) => (1 . 2)
consis often used to add a single element to the front of a list. This is called consing the element onto the list. 1 For example:(setq list (cons newelt list))Note that there is no conflict between the variable named
listused in this example and the function namedlistdescribed below; any symbol can serve both purposes.
This macro provides an alternative way to write
(setqlistname(consnewelt listname)). It is new in Emacs 21.(setq l '(a b)) => (a b) (push 'c l) => (c a b) l => (c a b)
This function creates a list with objects as its elements. The resulting list is always
nil-terminated. If no objects are given, the empty list is returned.(list 1 2 3 4 5) => (1 2 3 4 5) (list 1 2 '(3 4 5) 'foo) => (1 2 (3 4 5) foo) (list) => nil
This function creates a list of length elements, in which each element is object. Compare
make-listwithmake-string(see Creating Strings).(make-list 3 'pigs) => (pigs pigs pigs) (make-list 0 'pigs) => nil (setq l (make-list 3 '(a b)) => ((a b) (a b) (a b)) (eq (car l) (cadr l)) => t
This function returns a list containing all the elements of sequences. The sequences may be lists, vectors, bool-vectors, or strings, but the last one should usually be a list. All arguments except the last one are copied, so none of the arguments is altered. (See
nconcin Rearrangement, for a way to join lists with no copying.)More generally, the final argument to
appendmay be any Lisp object. The final argument is not copied or converted; it becomes the cdr of the last cons cell in the new list. If the final argument is itself a list, then its elements become in effect elements of the result list. If the final element is not a list, the result is a “dotted list” since its final cdr is notnilas required in a true list.The
appendfunction also allows integers as arguments. It converts them to strings of digits, making up the decimal print representation of the integer, and then uses the strings instead of the original integers. Don't use this feature; we plan to eliminate it. If you already use this feature, change your programs now! The proper way to convert an integer to a decimal number in this way is withformat(see Formatting Strings) ornumber-to-string(see String Conversion).
Here is an example of using append:
(setq trees '(pine oak))
=> (pine oak)
(setq more-trees (append '(maple birch) trees))
=> (maple birch pine oak)
trees
=> (pine oak)
more-trees
=> (maple birch pine oak)
(eq trees (cdr (cdr more-trees)))
=> t
You can see how append works by looking at a box diagram. The
variable trees is set to the list (pine oak) and then the
variable more-trees is set to the list (maple birch pine
oak). However, the variable trees continues to refer to the
original list:
more-trees trees
| |
| --- --- --- --- -> --- --- --- ---
--> | | |--> | | |--> | | |--> | | |--> nil
--- --- --- --- --- --- --- ---
| | | |
| | | |
--> maple -->birch --> pine --> oak
An empty sequence contributes nothing to the value returned by
append. As a consequence of this, a final nil argument
forces a copy of the previous argument:
trees
=> (pine oak)
(setq wood (append trees nil))
=> (pine oak)
wood
=> (pine oak)
(eq wood trees)
=> nil
This once was the usual way to copy a list, before the function
copy-sequence was invented. See Sequences Arrays Vectors.
Here we show the use of vectors and strings as arguments to append:
(append [a b] "cd" nil)
=> (a b 99 100)
With the help of apply (see Calling Functions), we can append
all the lists in a list of lists:
(apply 'append '((a b c) nil (x y z) nil))
=> (a b c x y z)
If no sequences are given, nil is returned:
(append)
=> nil
Here are some examples where the final argument is not a list:
(append '(x y) 'z)
=> (x y . z)
(append '(x y) [z])
=> (x y . [z])
The second example shows that when the final argument is a sequence but not a list, the sequence's elements do not become elements of the resulting list. Instead, the sequence becomes the final cdr, like any other non-list final argument.
This function creates a new list whose elements are the elements of list, but in reverse order. The original argument list is not altered.
(setq x '(1 2 3 4)) => (1 2 3 4) (reverse x) => (4 3 2 1) x => (1 2 3 4)
This function returns a copy of list, with all elements removed which are
eqto object. The letter ‘q’ inremqsays that it useseqto compare object against the elements oflist.(setq sample-list '(a b c a b c)) => (a b c a b c) (remq 'a sample-list) => (b c b c) sample-list => (a b c a b c)The function
delqoffers a way to perform this operation destructively. See Sets And Lists.
You can modify the car and cdr contents of a cons cell with the
primitives setcar and setcdr. We call these “destructive”
operations because they change existing list structure.
Common Lisp note: Common Lisp uses functionsrplacaandrplacdto alter list structure; they change structure the same way assetcarandsetcdr, but the Common Lisp functions return the cons cell whilesetcarandsetcdrreturn the new car or cdr.
setcarChanging the car of a cons cell is done with setcar. When
used on a list, setcar replaces one element of a list with a
different element.
This function stores object as the new car of cons, replacing its previous car. In other words, it changes the car slot of cons to refer to object. It returns the value object. For example:
(setq x '(1 2)) => (1 2) (setcar x 4) => 4 x => (4 2)
When a cons cell is part of the shared structure of several lists, storing a new car into the cons changes one element of each of these lists. Here is an example:
;; Create two lists that are partly shared. (setq x1 '(a b c)) => (a b c) (setq x2 (cons 'z (cdr x1))) => (z b c) ;; Replace the car of a shared link. (setcar (cdr x1) 'foo) => foo x1 ; Both lists are changed. => (a foo c) x2 => (z foo c) ;; Replace the car of a link that is not shared. (setcar x1 'baz) => baz x1 ; Only one list is changed. => (baz foo c) x2 => (z foo c)
Here is a graphical depiction of the shared structure of the two lists
in the variables x1 and x2, showing why replacing b
changes them both:
--- --- --- --- --- ---
x1---> | | |----> | | |--> | | |--> nil
--- --- --- --- --- ---
| --> | |
| | | |
--> a | --> b --> c
|
--- --- |
x2--> | | |--
--- ---
|
|
--> z
Here is an alternative form of box diagram, showing the same relationship:
x1:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| a | o------->| b | o------->| c | nil |
| | | -->| | | | | |
-------------- | -------------- --------------
|
x2: |
-------------- |
| car | cdr | |
| z | o----
| | |
--------------
The lowest-level primitive for modifying a cdr is setcdr:
This function stores object as the new cdr of cons, replacing its previous cdr. In other words, it changes the cdr slot of cons to refer to object. It returns the value object.
Here is an example of replacing the cdr of a list with a different list. All but the first element of the list are removed in favor of a different sequence of elements. The first element is unchanged, because it resides in the car of the list, and is not reached via the cdr.
(setq x '(1 2 3))
=> (1 2 3)
(setcdr x '(4))
=> (4)
x
=> (1 4)
You can delete elements from the middle of a list by altering the
cdrs of the cons cells in the list. For example, here we delete
the second element, b, from the list (a b c), by changing
the cdr of the first cons cell:
(setq x1 '(a b c))
=> (a b c)
(setcdr x1 (cdr (cdr x1)))
=> (c)
x1
=> (a c)
Here is the result in box notation:
--------------------
| |
-------------- | -------------- | --------------
| car | cdr | | | car | cdr | -->| car | cdr |
| a | o----- | b | o-------->| c | nil |
| | | | | | | | |
-------------- -------------- --------------
The second cons cell, which previously held the element b, still
exists and its car is still b, but it no longer forms part
of this list.
It is equally easy to insert a new element by changing cdrs:
(setq x1 '(a b c))
=> (a b c)
(setcdr x1 (cons 'd (cdr x1)))
=> (d b c)
x1
=> (a d b c)
Here is this result in box notation:
-------------- ------------- -------------
| car | cdr | | car | cdr | | car | cdr |
| a | o | -->| b | o------->| c | nil |
| | | | | | | | | | |
--------- | -- | ------------- -------------
| |
----- --------
| |
| --------------- |
| | car | cdr | |
-->| d | o------
| | |
---------------
Here are some functions that rearrange lists “destructively” by modifying the cdrs of their component cons cells. We call these functions “destructive” because they chew up the original lists passed to them as arguments, relinking their cons cells to form a new list that is the returned value.
See delq, in Sets And Lists, for another function
that modifies cons cells.
This function returns a list containing all the elements of lists. Unlike
append(see Building Lists), the lists are not copied. Instead, the last cdr of each of the lists is changed to refer to the following list. The last of the lists is not altered. For example:(setq x '(1 2 3)) => (1 2 3) (nconc x '(4 5)) => (1 2 3 4 5) x => (1 2 3 4 5)Since the last argument of
nconcis not itself modified, it is reasonable to use a constant list, such as'(4 5), as in the above example. For the same reason, the last argument need not be a list:(setq x '(1 2 3)) => (1 2 3) (nconc x 'z) => (1 2 3 . z) x => (1 2 3 . z)However, the other arguments (all but the last) must be lists.
A common pitfall is to use a quoted constant list as a non-last argument to
nconc. If you do this, your program will change each time you run it! Here is what happens:(defun add-foo (x) ; We want this function to add (nconc '(foo) x)) ;footo the front of its arg. (symbol-function 'add-foo) => (lambda (x) (nconc (quote (foo)) x)) (setq xx (add-foo '(1 2))) ; It seems to work. => (foo 1 2) (setq xy (add-foo '(3 4))) ; What happened? => (foo 1 2 3 4) (eq xx xy) => t (symbol-function 'add-foo) => (lambda (x) (nconc (quote (foo 1 2 3 4) x)))
This function reverses the order of the elements of list. Unlike
reverse,nreversealters its argument by reversing the cdrs in the cons cells forming the list. The cons cell that used to be the last one in list becomes the first cons cell of the value.For example:
(setq x '(a b c)) => (a b c) x => (a b c) (nreverse x) => (c b a) ;; The cons cell that was first is now last. x => (a)To avoid confusion, we usually store the result of
nreverseback in the same variable which held the original list:(setq x (nreverse x))Here is the
nreverseof our favorite example,(a b c), presented graphically:Original list head: Reversed list: ------------- ------------- ------------ | car | cdr | | car | cdr | | car | cdr | | a | nil |<-- | b | o |<-- | c | o | | | | | | | | | | | | | | ------------- | --------- | - | -------- | - | | | | ------------- ------------
This function sorts list stably, though destructively, and returns the sorted list. It compares elements using predicate. A stable sort is one in which elements with equal sort keys maintain their relative order before and after the sort. Stability is important when successive sorts are used to order elements according to different criteria.
The argument predicate must be a function that accepts two arguments. It is called with two elements of list. To get an increasing order sort, the predicate should return
tif the first element is “less than” the second, ornilif not.The comparison function predicate must give reliable results for any given pair of arguments, at least within a single call to
sort. It must be antisymmetric; that is, if a is less than b, b must not be less than a. It must be transitive—that is, if a is less than b, and b is less than c, then a must be less than c. If you use a comparison function which does not meet these requirements, the result ofsortis unpredictable.The destructive aspect of
sortis that it rearranges the cons cells forming list by changing cdrs. A nondestructive sort function would create new cons cells to store the elements in their sorted order. If you wish to make a sorted copy without destroying the original, copy it first withcopy-sequenceand then sort.Sorting does not change the cars of the cons cells in list; the cons cell that originally contained the element
ain list still hasain its car after sorting, but it now appears in a different position in the list due to the change of cdrs. For example:(setq nums '(1 3 2 6 5 4 0)) => (1 3 2 6 5 4 0) (sort nums '<) => (0 1 2 3 4 5 6) nums => (1 2 3 4 5 6)Warning: Note that the list in
numsno longer contains 0; this is the same cons cell that it was before, but it is no longer the first one in the list. Don't assume a variable that formerly held the argument now holds the entire sorted list! Instead, save the result ofsortand use that. Most often we store the result back into the variable that held the original list:(setq nums (sort nums '<))See Sorting, for more functions that perform sorting. See
documentationin Accessing Documentation, for a useful example ofsort.
A list can represent an unordered mathematical set—simply consider a
value an element of a set if it appears in the list, and ignore the
order of the list. To form the union of two sets, use append (as
long as you don't mind having duplicate elements). Other useful
functions for sets include memq and delq, and their
equal versions, member and delete.
Common Lisp note: Common Lisp has functionsunion(which avoids duplicate elements) andintersectionfor set operations, but GNU Emacs Lisp does not have them. You can write them in Lisp if you wish.
This function tests to see whether object is a member of list. If it is,
memqreturns a list starting with the first occurrence of object. Otherwise, it returnsnil. The letter ‘q’ inmemqsays that it useseqto compare object against the elements of the list. For example:(memq 'b '(a b c b a)) => (b c b a) (memq '(2) '((1) (2))) ;(2)and(2)are noteq. => nil
This function is like
member, except that it ignores differences in letter-case and text representation: upper-case and lower-case letters are treated as equal, and unibyte strings are converted to multibyte prior to comparison.
This function destructively removes all elements
eqto object from list. The letter ‘q’ indelqsays that it useseqto compare object against the elements of the list, likememqandremq.
When delq deletes elements from the front of the list, it does so
simply by advancing down the list and returning a sublist that starts
after those elements:
(delq 'a '(a b c)) == (cdr '(a b c))
When an element to be deleted appears in the middle of the list, removing it involves changing the cdrs (see Setcdr).
(setq sample-list '(a b c (4)))
=> (a b c (4))
(delq 'a sample-list)
=> (b c (4))
sample-list
=> (a b c (4))
(delq 'c sample-list)
=> (a b (4))
sample-list
=> (a b (4))
Note that (delq 'c sample-list) modifies sample-list to
splice out the third element, but (delq 'a sample-list) does not
splice anything—it just returns a shorter list. Don't assume that a
variable which formerly held the argument list now has fewer
elements, or that it still holds the original list! Instead, save the
result of delq and use that. Most often we store the result back
into the variable that held the original list:
(setq flowers (delq 'rose flowers))
In the following example, the (4) that delq attempts to match
and the (4) in the sample-list are not eq:
(delq '(4) sample-list)
=> (a c (4))
The following two functions are like memq and delq but use
equal rather than eq to compare elements. See Equality Predicates.
The function
membertests to see whether object is a member of list, comparing members with object usingequal. If object is a member,memberreturns a list starting with its first occurrence in list. Otherwise, it returnsnil.Compare this with
memq:(member '(2) '((1) (2))) ;(2)and(2)areequal. => ((2)) (memq '(2) '((1) (2))) ;(2)and(2)are noteq. => nil ;; Two strings with the same contents areequal. (member "foo" '("foo" "bar")) => ("foo" "bar")
If
sequenceis a list, this function destructively removes all elementsequalto object from sequence. For lists,deleteis todelqasmemberis tomemq: it usesequalto compare elements with object, likemember; when it finds an element that matches, it removes the element just asdelqwould.If
sequenceis a vector or string,deletereturns a copy ofsequencewith all elementsequaltoobjectremoved.For example:
(delete '(2) '((2) (1) (2))) => ((1)) (delete '(2) [(2) (1) (2)]) => [(1)]
This function is the non-destructive counterpart of
delete. If returns a copy ofsequence, a list, vector, or string, with elementsequaltoobjectremoved. For example:(remove '(2) '((2) (1) (2))) => ((1)) (remove '(2) [(2) (1) (2)]) => [(1)]
Common Lisp note: The functionsmember,deleteandremovein GNU Emacs Lisp are derived from Maclisp, not Common Lisp. The Common Lisp versions do not useequalto compare elements.
See also the function add-to-list, in Setting Variables,
for another way to add an element to a list stored in a variable.
An association list, or alist for short, records a mapping from keys to values. It is a list of cons cells called associations: the car of each cons cell is the key, and the cdr is the associated value.2
Here is an example of an alist. The key pine is associated with
the value cones; the key oak is associated with
acorns; and the key maple is associated with seeds.
((pine . cones)
(oak . acorns)
(maple . seeds))
The associated values in an alist may be any Lisp objects; so may the
keys. For example, in the following alist, the symbol a is
associated with the number 1, and the string "b" is
associated with the list (2 3), which is the cdr of
the alist element:
((a . 1) ("b" 2 3))
Sometimes it is better to design an alist to store the associated value in the car of the cdr of the element. Here is an example of such an alist:
((rose red) (lily white) (buttercup yellow))
Here we regard red as the value associated with rose. One
advantage of this kind of alist is that you can store other related
information—even a list of other items—in the cdr of the
cdr. One disadvantage is that you cannot use rassq (see
below) to find the element containing a given value. When neither of
these considerations is important, the choice is a matter of taste, as
long as you are consistent about it for any given alist.
Note that the same alist shown above could be regarded as having the
associated value in the cdr of the element; the value associated
with rose would be the list (red).
Association lists are often used to record information that you might otherwise keep on a stack, since new associations may be added easily to the front of the list. When searching an association list for an association with a given key, the first one found is returned, if there is more than one.
In Emacs Lisp, it is not an error if an element of an association list is not a cons cell. The alist search functions simply ignore such elements. Many other versions of Lisp signal errors in such cases.
Note that property lists are similar to association lists in several respects. A property list behaves like an association list in which each key can occur only once. See Property Lists, for a comparison of property lists and association lists.
This function returns the first association for key in alist. It compares key against the alist elements using
equal(see Equality Predicates). It returnsnilif no association in alist has a carequalto key. For example:(setq trees '((pine . cones) (oak . acorns) (maple . seeds))) => ((pine . cones) (oak . acorns) (maple . seeds)) (assoc 'oak trees) => (oak . acorns) (cdr (assoc 'oak trees)) => acorns (assoc 'birch trees) => nilHere is another example, in which the keys and values are not symbols:
(setq needles-per-cluster '((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine"))) (cdr (assoc 3 needles-per-cluster)) => ("Pitch Pine") (cdr (assoc 2 needles-per-cluster)) => ("Austrian Pine" "Red Pine")
The functions assoc-ignore-representation and
assoc-ignore-case are much like assoc except using
compare-strings to do the comparison. See Text Comparison.
This function returns the first association with value value in alist. It returns
nilif no association in alist has a cdrequalto value.
rassocis likeassocexcept that it compares the cdr of each alist association instead of the car. You can think of this as “reverseassoc”, finding the key for a given value.
This function is like
associn that it returns the first association for key in alist, but it makes the comparison usingeqinstead ofequal.assqreturnsnilif no association in alist has a careqto key. This function is used more often thanassoc, sinceeqis faster thanequaland most alists use symbols as keys. See Equality Predicates.(setq trees '((pine . cones) (oak . acorns) (maple . seeds))) => ((pine . cones) (oak . acorns) (maple . seeds)) (assq 'pine trees) => (pine . cones)On the other hand,
assqis not usually useful in alists where the keys may not be symbols:(setq leaves '(("simple leaves" . oak) ("compound leaves" . horsechestnut))) (assq "simple leaves" leaves) => nil (assoc "simple leaves" leaves) => ("simple leaves" . oak)
This function returns the first association with value value in alist. It returns
nilif no association in alist has a cdreqto value.
rassqis likeassqexcept that it compares the cdr of each alist association instead of the car. You can think of this as “reverseassq”, finding the key for a given value.For example:
(setq trees '((pine . cones) (oak . acorns) (maple . seeds))) (rassq 'acorns trees) => (oak . acorns) (rassq 'spores trees) => nilNote that
rassqcannot search for a value stored in the car of the cdr of an element:(setq colors '((rose red) (lily white) (buttercup yellow))) (rassq 'white colors) => nilIn this case, the cdr of the association
(lily white)is not the symbolwhite, but rather the list(white). This becomes clearer if the association is written in dotted pair notation:(lily white) == (lily . (white))
This function searches alist for a match for key. For each element of alist, it compares the element (if it is an atom) or the element's car (if it is a cons) against key, by calling test with two arguments: the element or its car, and key. The arguments are passed in that order so that you can get useful results using
string-matchwith an alist that contains regular expressions (see Regexp Search). If test is omitted ornil,equalis used for comparison.If an alist element matches key by this criterion, then
assoc-defaultreturns a value based on this element. If the element is a cons, then the value is the element's cdr. Otherwise, the return value is default.If no alist element matches key,
assoc-defaultreturnsnil.
This function returns a two-level deep copy of alist: it creates a new copy of each association, so that you can alter the associations of the new alist without changing the old one.
(setq needles-per-cluster '((2 . ("Austrian Pine" "Red Pine")) (3 . ("Pitch Pine")) (5 . ("White Pine")))) => ((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine")) (setq copy (copy-alist needles-per-cluster)) => ((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine")) (eq needles-per-cluster copy) => nil (equal needles-per-cluster copy) => t (eq (car needles-per-cluster) (car copy)) => nil (cdr (car (cdr needles-per-cluster))) => ("Pitch Pine") (eq (cdr (car (cdr needles-per-cluster))) (cdr (car (cdr copy)))) => tThis example shows how
copy-alistmakes it possible to change the associations of one copy without affecting the other:(setcdr (assq 3 copy) '("Martian Vacuum Pine")) (cdr (assq 3 needles-per-cluster)) => ("Pitch Pine")
This function deletes from alist all the elements whose car is
eqto key. It returns alist, modified in this way. Note that it modifies the original list structure of alist.(assq-delete-all 'foo '((foo 1) (bar 2) (foo 3) (lose 4))) => ((bar 2) (lose 4))
Recall that the sequence type is the union of two other Lisp types: lists and arrays. In other words, any list is a sequence, and any array is a sequence. The common property that all sequences have is that each is an ordered collection of elements.
An array is a single primitive object that has a slot for each of its elements. All the elements are accessible in constant time, but the length of an existing array cannot be changed. Strings, vectors, char-tables and bool-vectors are the four types of arrays.
A list is a sequence of elements, but it is not a single primitive object; it is made of cons cells, one cell per element. Finding the nth element requires looking through n cons cells, so elements farther from the beginning of the list take longer to access. But it is possible to add elements to the list, or remove elements.
The following diagram shows the relationship between these types:
_____________________________________________
| |
| Sequence |
| ______ ________________________________ |
| | | | | |
| | List | | Array | |
| | | | ________ ________ | |
| |______| | | | | | | |
| | | Vector | | String | | |
| | |________| |________| | |
| | ____________ _____________ | |
| | | | | | | |
| | | Char-table | | Bool-vector | | |
| | |____________| |_____________| | |
| |________________________________| |
|_____________________________________________|
The elements of vectors and lists may be any Lisp objects. The elements of strings are all characters.
In Emacs Lisp, a sequence is either a list or an array. The common property of all sequences is that they are ordered collections of elements. This section describes functions that accept any kind of sequence.
This function returns the number of elements in sequence. If sequence is a cons cell that is not a list (because the final cdr is not
nil), awrong-type-argumenterror is signaled.See List Elements, for the related function
safe-length.(length '(1 2 3)) => 3 (length ()) => 0 (length "foobar") => 6 (length [1 2 3]) => 3 (length (make-bool-vector 5 nil)) => 5
This function returns the element of sequence indexed by index. Legitimate values of index are integers ranging from 0 up to one less than the length of sequence. If sequence is a list, then out-of-range values of index return
nil; otherwise, they trigger anargs-out-of-rangeerror.(elt [1 2 3 4] 2) => 3 (elt '(1 2 3 4) 2) => 3 ;; We usestringto show clearly which charactereltreturns. (string (elt "1234" 2)) => "3" (elt [1 2 3 4] 4) error--> Args out of range: [1 2 3 4], 4 (elt [1 2 3 4] -1) error--> Args out of range: [1 2 3 4], -1This function generalizes
aref(see Array Functions) andnth(see List Elements).
Returns a copy of sequence. The copy is the same type of object as the original sequence, and it has the same elements in the same order.
Storing a new element into the copy does not affect the original sequence, and vice versa. However, the elements of the new sequence are not copies; they are identical (
eq) to the elements of the original. Therefore, changes made within these elements, as found via the copied sequence, are also visible in the original sequence.If the sequence is a string with text properties, the property list in the copy is itself a copy, not shared with the original's property list. However, the actual values of the properties are shared. See Text Properties.
See also
appendin Building Lists,concatin Creating Strings, andvconcatin Vectors, for other ways to copy sequences.(setq bar '(1 2)) => (1 2) (setq x (vector 'foo bar)) => [foo (1 2)] (setq y (copy-sequence x)) => [foo (1 2)] (eq x y) => nil (equal x y) => t (eq (elt x 1) (elt y 1)) => t ;; Replacing an element of one sequence. (aset x 0 'quux) x => [quux (1 2)] y => [foo (1 2)] ;; Modifying the inside of a shared element. (setcar (aref x 1) 69) x => [quux (69 2)] y => [foo (69 2)]
An array object has slots that hold a number of other Lisp objects, called the elements of the array. Any element of an array may be accessed in constant time. In contrast, an element of a list requires access time that is proportional to the position of the element in the list.
Emacs defines four types of array, all one-dimensional: strings, vectors, bool-vectors and char-tables. A vector is a general array; its elements can be any Lisp objects. A string is a specialized array; its elements must be characters. Each type of array has its own read syntax. See String Type, and Vector Type.
All four kinds of array share these characteristics:
aref and aset, respectively (see Array Functions).
When you create an array, other than a char-table, you must specify its length. You cannot specify the length of a char-table, because that is determined by the range of character codes.
In principle, if you want an array of text characters, you could use either a string or a vector. In practice, we always choose strings for such applications, for four reasons:
By contrast, for an array of keyboard input characters (such as a key sequence), a vector may be necessary, because many keyboard input characters are outside the range that will fit in a string. See Key Sequence Input.
In this section, we describe the functions that accept all types of arrays.
This function returns
tif object is an array (i.e., a vector, a string, a bool-vector or a char-table).(arrayp [a]) => t (arrayp "asdf") => t (arrayp (syntax-table)) ;; A char-table. => t
This function returns the indexth element of array. The first element is at index zero.
(setq primes [2 3 5 7 11 13]) => [2 3 5 7 11 13] (aref primes 4) => 11 (aref "abcdefg" 1) => 98 ; ‘b’ is ascii code 98.See also the function
elt, in Sequence Functions.
This function sets the indexth element of array to be object. It returns object.
(setq w [foo bar baz]) => [foo bar baz] (aset w 0 'fu) => fu w => [fu bar baz] (setq x "asdfasfd") => "asdfasfd" (aset x 3 ?Z) => 90 x => "asdZasfd"If array is a string and object is not a character, a
wrong-type-argumenterror results. The function converts a unibyte string to multibyte if necessary to insert a character.
This function fills the array array with object, so that each element of array is object. It returns array.
(setq a [a b c d e f g]) => [a b c d e f g] (fillarray a 0) => [0 0 0 0 0 0 0] a => [0 0 0 0 0 0 0] (setq s "When in the course") => "When in the course" (fillarray s ?-) => "------------------"If array is a string and object is not a character, a
wrong-type-argumenterror results.
The general sequence functions copy-sequence and length
are often useful for objects known to be arrays. See Sequence Functions.
Arrays in Lisp, like arrays in most languages, are blocks of memory whose elements can be accessed in constant time. A vector is a general-purpose array of specified length; its elements can be any Lisp objects. (By contrast, a string can hold only characters as elements.) Vectors in Emacs are used for obarrays (vectors of symbols), and as part of keymaps (vectors of commands). They are also used internally as part of the representation of a byte-compiled function; if you print such a function, you will see a vector in it.
In Emacs Lisp, the indices of the elements of a vector start from zero and count up from there.
Vectors are printed with square brackets surrounding the elements.
Thus, a vector whose elements are the symbols a, b and
a is printed as [a b a]. You can write vectors in the
same way in Lisp input.
A vector, like a string or a number, is considered a constant for evaluation: the result of evaluating it is the same vector. This does not evaluate or even examine the elements of the vector. See Self-Evaluating Forms.
Here are examples illustrating these principles:
(setq avector [1 two '(three) "four" [five]])
=> [1 two (quote (three)) "four" [five]]
(eval avector)
=> [1 two (quote (three)) "four" [five]]
(eq avector (eval avector))
=> t
Here are some functions that relate to vectors:
This function returns
tif object is a vector.(vectorp [a]) => t (vectorp "asdf") => nil
This function creates and returns a vector whose elements are the arguments, objects.
(vector 'foo 23 [bar baz] "rats") => [foo 23 [bar baz] "rats"] (vector) => []
This function returns a new vector consisting of length elements, each initialized to object.
(setq sleepy (make-vector 9 'Z)) => [Z Z Z Z Z Z Z Z Z]
This function returns a new vector containing all the elements of the sequences. The arguments sequences may be any kind of arrays, including lists, vectors, or strings. If no sequences are given, an empty vector is returned.
The value is a newly constructed vector that is not
eqto any existing vector.(setq a (vconcat '(A B C) '(D E F))) => [A B C D E F] (eq a (vconcat a)) => nil (vconcat) => [] (vconcat [A B C] "aa" '(foo (6 7))) => [A B C 97 97 foo (6 7)]The
vconcatfunction also allows byte-code function objects as arguments. This is a special feature to make it easy to access the entire contents of a byte-code function object. See Byte-Code Objects.The
vconcatfunction also allows integers as arguments. It converts them to strings of digits, making up the decimal print representation of the integer, and then uses the strings instead of the original integers. Don't use this feature; we plan to eliminate it. If you already use this feature, change your programs now! The proper way to convert an integer to a decimal number in this way is withformat(see Formatting Strings) ornumber-to-string(see String Conversion).For other concatenation functions, see
mapconcatin Mapping Functions,concatin Creating Strings, andappendin Building Lists.
The append function provides a way to convert a vector into a
list with the same elements (see Building Lists):
(setq avector [1 two (quote (three)) "four" [five]])
=> [1 two (quote (three)) "four" [five]]
(append avector nil)
=> (1 two (quote (three)) "four" [five])
A char-table is much like a vector, except that it is indexed by
character codes. Any valid character code, without modifiers, can be
used as an index in a char-table. You can access a char-table's
elements with aref and aset, as with any array. In
addition, a char-table can have extra slots to hold additional
data not associated with particular character codes. Char-tables are
constants when evaluated.
Each char-table has a subtype which is a symbol. The subtype
has two purposes: to distinguish char-tables meant for different uses,
and to control the number of extra slots. For example, display tables
are char-tables with display-table as the subtype, and syntax
tables are char-tables with syntax-table as the subtype. A valid
subtype must have a char-table-extra-slots property which is an
integer between 0 and 10. This integer specifies the number of
extra slots in the char-table.
A char-table can have a parent, which is another char-table. If
it does, then whenever the char-table specifies nil for a
particular character c, it inherits the value specified in the
parent. In other words, (aref char-table c) returns
the value from the parent of char-table if char-table itself
specifies nil.
A char-table can also have a default value. If so, then
(aref char-table c) returns the default value
whenever the char-table does not specify any other non-nil value.
Return a newly created char-table, with subtype subtype. Each element is initialized to init, which defaults to
nil. You cannot alter the subtype of a char-table after the char-table is created.There is no argument to specify the length of the char-table, because all char-tables have room for any valid character code as an index.
This function sets the default value of char-table to new-default.
There is no special function to access the default value of a char-table. To do that, use
(char-table-rangechar-tablenil).
This function returns the parent of char-table. The parent is always either
nilor another char-table.
This function sets the parent of char-table to new-parent.
This function returns the contents of extra slot n of char-table. The number of extra slots in a char-table is determined by its subtype.
This function stores value in extra slot n of char-table.
A char-table can specify an element value for a single character code; it can also specify a value for an entire character set.
This returns the value specified in char-table for a range of characters range. Here are the possibilities for range:
nil- Refers to the default value.
- char
- Refers to the element for character char (supposing char is a valid character code).
- charset
- Refers to the value specified for the whole character set charset (see Character Sets).
- generic-char
- A generic character stands for a character set; specifying the generic character as argument is equivalent to specifying the character set name. See Splitting Characters, for a description of generic characters.
This function sets the value in char-table for a range of characters range. Here are the possibilities for range:
nil- Refers to the default value.
t- Refers to the whole range of character codes.
- char
- Refers to the element for character char (supposing char is a valid character code).
- charset
- Refers to the value specified for the whole character set charset (see Character Sets).
- generic-char
- A generic character stands for a character set; specifying the generic character as argument is equivalent to specifying the character set name. See Splitting Characters, for a description of generic characters.
This function calls function for each element of char-table. function is called with two arguments, a key and a value. The key is a possible range argument for
char-table-range—either a valid character or a generic character—and the value is(char-table-rangechar-table key).Overall, the key-value pairs passed to function describe all the values stored in char-table.
The return value is always
nil; to make this function useful, function should have side effects. For example, here is how to examine each element of the syntax table:(let (accumulator) (map-char-table #'(lambda (key value) (setq accumulator (cons (list key value) accumulator))) (syntax-table)) accumulator) => ((475008 nil) (474880 nil) (474752 nil) (474624 nil) ... (5 (3)) (4 (3)) (3 (3)) (2 (3)) (1 (3)) (0 (3)))
A bool-vector is much like a vector, except that it stores only the
values t and nil. If you try to store any non-nil
value into an element of the bool-vector, the effect is to store
t there. As with all arrays, bool-vector indices start from 0,
and the length cannot be changed once the bool-vector is created.
Bool-vectors are constants when evaluated.
There are two special functions for working with bool-vectors; aside from that, you manipulate them with same functions used for other kinds of arrays.
Return a new bool-vector of length elements, each one initialized to initial.
Here is an example of creating, examining, and updating a bool-vector. Note that the printed form represents up to 8 boolean values as a single character.
(setq bv (make-bool-vector 5 t))
=> #&5"^_"
(aref bv 1)
=> t
(aset bv 3 nil)
=> nil
bv
=> #&5"^W"
These results make sense because the binary codes for control-_ and control-W are 11111 and 10111, respectively.
A hash table is a very fast kind of lookup table, somewhat like an alist in that it maps keys to corresponding values. It differs from an alist in these ways:
Emacs Lisp (starting with Emacs 21) provides a general-purpose hash table data type, along with a series of functions for operating on them. Hash tables have no read syntax, and print in hash notation, like this:
(make-hash-table)
=> #<hash-table 'eql nil 0/65 0x83af980>
(The term “hash notation” refers to the initial ‘#’ character—see Printed Representation—and has nothing to do with the term “hash table.”)
Obarrays are also a kind of hash table, but they are a different type of object and are used only for recording interned symbols (see Creating Symbols).
The principal function for creating a hash table is
make-hash-table.
This function creates a new hash table according to the specified arguments. The arguments should consist of alternating keywords (particular symbols recognized specially) and values corresponding to them.
Several keywords make sense in
make-hash-table, but the only two that you really need to know about are:testand:weakness.
:testtest- This specifies the method of key lookup for this hash table. The default is
eql;eqandequalare other alternatives:
eql- Keys which are numbers are “the same” if they are equal in value; otherwise, two distinct objects are never “the same”.
eq- Any two distinct Lisp objects are “different” as keys.
equal- Two Lisp objects are “the same”, as keys, if they are equal according to
equal.You can use
define-hash-table-test(see Defining Hash) to define additional possibilities for test.:weaknessweak- The weakness of a hash table specifies whether the presence of a key or value in the hash table preserves it from garbage collection.
The value, weak, must be one of
nil,key,value,key-or-value,key-and-value, ortwhich is an alias forkey-and-value. If weak iskeythen the hash table does not prevent its keys from being collected as garbage (if they are not referenced anywhere else); if a particular key does get collected, the corresponding association is removed from the hash table.If weak is
value, then the hash table does not prevent values from being collected as garbage (if they are not referenced anywhere else); if a particular value does get collected, the corresponding association is removed from the hash table.If weak is
key-or-valueort, the hash table does not protect either keys or values from garbage collection; if either one is collected as garbage, the association is removed.If weak is
key-and-value, associations are removed from the hash table when both their key and value would be collected as garbage, again not considering references to the key and value from weak hash tables.The default for weak is
nil, so that all keys and values referenced in the hash table are preserved from garbage collection. If weak ist, neither keys nor values are protected (that is, both are weak).:sizesize- This specifies a hint for how many associations you plan to store in the hash table. If you know the approximate number, you can make things a little more efficient by specifying it this way. If you specify too small a size, the hash table will grow automatically when necessary, but doing that takes some extra time.
The default size is 65.
:rehash-sizerehash-size- When you add an association to a hash table and the table is “full,” it grows automatically. This value specifies how to make the hash table larger, at that time.
If rehash-size is an integer, it should be positive, and the hash table grows by adding that much to the nominal size. If rehash-size is a floating point number, it had better be greater than 1, and the hash table grows by multiplying the old size by that number.
The default value is 1.5.
:rehash-thresholdthreshold- This specifies the criterion for when the hash table is “full.” The value, threshold, should be a positive floating point number, no greater than 1. The hash table is “full” whenever the actual number of entries exceeds this fraction of the nominal size. The default for threshold is 0.8.
This is equivalent to
make-hash-table, but with a different style argument list. The argument test specifies the method of key lookup.If you want to specify other parameters, you should use
make-hash-table.
This section describes the functions for accessing and storing associations in a hash table.
This function looks up key in table, and returns its associated value—or default, if key has no association in table.
This function enters an association for key in table, with value value. If key already has an association in table, value replaces the old associated value.
This function removes the association for key from table, if there is one. If key has no association,
remhashdoes nothing.
This function removes all the associations from hash table table, so that it becomes empty. This is also called clearing the hash table.
This function calls function once for each of the associations in table. The function function should accept two arguments—a key listed in table, and its associated value.
You can define new methods of key lookup by means of
define-hash-table-test. In order to use this feature, you need
to understand how hash tables work, and what a hash code means.
You can think of a hash table conceptually as a large array of many
slots, each capable of holding one association. To look up a key,
gethash first computes an integer, the hash code, from the key.
It reduces this integer modulo the length of the array, to produce an
index in the array. Then it looks in that slot, and if necessary in
other nearby slots, to see if it has found the key being sought.
Thus, to define a new method of key lookup, you need to specify both a function to compute the hash code from a key, and a function to compare two keys directly.
This function defines a new hash table test, named name.
After defining name in this way, you can use it as the test argument in
make-hash-table. When you do that, the hash table will use test-fn to compare key values, and hash-fn to compute a “hash code” from a key value.The function test-fn should accept two arguments, two keys, and return non-
nilif they are considered “the same.”The function hash-fn should accept one argument, a key, and return an integer that is the “hash code” of that key. For good results, the function should use the whole range of integer values for hash codes, including negative integers.
The specified functions are stored in the property list of name under the property
hash-table-test; the property value's form is(test-fn hash-fn).
This function returns a hash code for Lisp object obj. This is an integer which reflects the contents of obj and the other Lisp objects it points to.
If two objects obj1 and obj2 are equal, then
(sxhashobj1)and(sxhashobj2)are the same integer.If the two objects are not equal, the values returned by
sxhashare usually different, but not always; but once in a rare while, by luck, you will encounter two distinct-looking objects that give the same result fromsxhash.
This example creates a hash table whose keys are strings that are compared case-insensitively.
(defun case-fold-string= (a b)
(compare-strings a nil nil b nil nil t))
(defun case-fold-string-hash (a)
(sxhash (upcase a)))
(define-hash-table-test 'case-fold 'case-fold-string=
'case-fold-string-hash))
(make-hash-table :test 'case-fold)
Here is how you could define a hash table test equivalent to the
predefined test value equal. The keys can be any Lisp object,
and equal-looking objects are considered the same key.
(define-hash-table-test 'contents-hash 'equal 'sxhash)
(make-hash-table :test 'contents-hash)
Here are some other functions for working with hash tables.
This function creates and returns a copy of table. Only the table itself is copied—the keys and values are shared.
This returns the test value that was given when table was created, to specify how to hash and compare keys. See
make-hash-table(see Creating Hash).
This function returns the weak value that was specified for hash table table.
A symbol is an object with a unique name. This chapter describes symbols, their components, their property lists, and how they are created and interned. Separate chapters describe the use of symbols as variables and as function names; see Variables, and Functions. For the precise read syntax for symbols, see Symbol Type.
You can test whether an arbitrary Lisp object is a symbol
with symbolp:
Each symbol has four components (or “cells”), each of which references another object:
symbol-name in Creating Symbols.
symbol-value in
Accessing Variables.
symbol-function in Function Cells.
symbol-plist in Property Lists.
The print name cell always holds a string, and cannot be changed. The other three cells can be set individually to any specified Lisp object.
The print name cell holds the string that is the name of the symbol. Since symbols are represented textually by their names, it is important not to have two symbols with the same name. The Lisp reader ensures this: every time it reads a symbol, it looks for an existing symbol with the specified name before it creates a new one. (In GNU Emacs Lisp, this lookup uses a hashing algorithm and an obarray; see Creating Symbols.)
The value cell holds the symbol's value as a variable
(see Variables). That is what you get if you evaluate the symbol as
a Lisp expression (see Evaluation). Any Lisp object is a legitimate
value. Certain symbols have values that cannot be changed; these
include nil and t, and any symbol whose name starts with
‘:’ (those are called keywords). See Constant Variables.
We often refer to “the function foo” when we really mean
the function stored in the function cell of the symbol foo. We
make the distinction explicit only when necessary. In normal
usage, the function cell usually contains a function
(see Functions) or a macro (see Macros), as that is what the
Lisp interpreter expects to see there (see Evaluation). Keyboard
macros (see Keyboard Macros), keymaps (see Keymaps) and
autoload objects (see Autoloading) are also sometimes stored in
the function cells of symbols.
The property list cell normally should hold a correctly formatted property list (see Property Lists), as a number of functions expect to see a property list there.
The function cell or the value cell may be void, which means
that the cell does not reference any object. (This is not the same
thing as holding the symbol void, nor the same as holding the
symbol nil.) Examining a function or value cell that is void
results in an error, such as ‘Symbol's value as variable is void’.
The four functions symbol-name, symbol-value,
symbol-plist, and symbol-function return the contents of
the four cells of a symbol. Here as an example we show the contents of
the four cells of the symbol buffer-file-name:
(symbol-name 'buffer-file-name)
=> "buffer-file-name"
(symbol-value 'buffer-file-name)
=> "/gnu/elisp/symbols.texi"
(symbol-plist 'buffer-file-name)
=> (variable-documentation 29529)
(symbol-function 'buffer-file-name)
=> #<subr buffer-file-name>
Because this symbol is the variable which holds the name of the file
being visited in the current buffer, the value cell contents we see are
the name of the source file of this chapter of the Emacs Lisp Manual.
The property list cell contains the list (variable-documentation
29529) which tells the documentation functions where to find the
documentation string for the variable buffer-file-name in the
DOC-version file. (29529 is the offset from the beginning
of the DOC-version file to where that documentation string
begins—see Documentation Basics.) The function cell contains
the function for returning the name of the file.
buffer-file-name names a primitive function, which has no read
syntax and prints in hash notation (see Primitive Function Type). A
symbol naming a function written in Lisp would have a lambda expression
(or a byte-code object) in this cell.
A definition in Lisp is a special form that announces your intention to use a certain symbol in a particular way. In Emacs Lisp, you can define a symbol as a variable, or define it as a function (or macro), or both independently.
A definition construct typically specifies a value or meaning for the symbol for one kind of use, plus documentation for its meaning when used in this way. Thus, when you define a symbol as a variable, you can supply an initial value for the variable, plus documentation for the variable.
defvar and defconst are special forms that define a
symbol as a global variable. They are documented in detail in
Defining Variables. For defining user option variables that can
be customized, use defcustom (see Customization).
defun defines a symbol as a function, creating a lambda
expression and storing it in the function cell of the symbol. This
lambda expression thus becomes the function definition of the symbol.
(The term “function definition”, meaning the contents of the function
cell, is derived from the idea that defun gives the symbol its
definition as a function.) defsubst and defalias are two
other ways of defining a function. See Functions.
defmacro defines a symbol as a macro. It creates a macro
object and stores it in the function cell of the symbol. Note that a
given symbol can be a macro or a function, but not both at once, because
both macro and function definitions are kept in the function cell, and
that cell can hold only one Lisp object at any given time.
See Macros.
In Emacs Lisp, a definition is not required in order to use a symbol
as a variable or function. Thus, you can make a symbol a global
variable with setq, whether you define it first or not. The real
purpose of definitions is to guide programmers and programming tools.
They inform programmers who read the code that certain symbols are
intended to be used as variables, or as functions. In addition,
utilities such as etags and make-docfile recognize
definitions, and add appropriate information to tag tables and the
DOC-version file. See Accessing Documentation.
To understand how symbols are created in GNU Emacs Lisp, you must know how Lisp reads them. Lisp must ensure that it finds the same symbol every time it reads the same set of characters. Failure to do so would cause complete confusion.
When the Lisp reader encounters a symbol, it reads all the characters of the name. Then it “hashes” those characters to find an index in a table called an obarray. Hashing is an efficient method of looking something up. For example, instead of searching a telephone book cover to cover when looking up Jan Jones, you start with the J's and go from there. That is a simple version of hashing. Each element of the obarray is a bucket which holds all the symbols with a given hash code; to look for a given name, it is sufficient to look through all the symbols in the bucket for that name's hash code. (The same idea is used for general Emacs hash tables, but they are a different data type; see Hash Tables.)
If a symbol with the desired name is found, the reader uses that symbol. If the obarray does not contain a symbol with that name, the reader makes a new symbol and adds it to the obarray. Finding or adding a symbol with a certain name is called interning it, and the symbol is then called an interned symbol.
Interning ensures that each obarray has just one symbol with any particular name. Other like-named symbols may exist, but not in the same obarray. Thus, the reader gets the same symbols for the same names, as long as you keep reading with the same obarray.
Interning usually happens automatically in the reader, but sometimes other programs need to do it. For example, after the M-x command obtains the command name as a string using the minibuffer, it then interns the string, to get the interned symbol with that name.
No obarray contains all symbols; in fact, some symbols are not in any obarray. They are called uninterned symbols. An uninterned symbol has the same four cells as other symbols; however, the only way to gain access to it is by finding it in some other object or as the value of a variable.
Creating an uninterned symbol is useful in generating Lisp code, because an uninterned symbol used as a variable in the code you generate cannot clash with any variables used in other Lisp programs.
In Emacs Lisp, an obarray is actually a vector. Each element of the
vector is a bucket; its value is either an interned symbol whose name
hashes to that bucket, or 0 if the bucket is empty. Each interned
symbol has an internal link (invisible to the user) to the next symbol
in the bucket. Because these links are invisible, there is no way to
find all the symbols in an obarray except using mapatoms (below).
The order of symbols in a bucket is not significant.
In an empty obarray, every element is 0, so you can create an obarray
with (make-vector length 0). This is the only
valid way to create an obarray. Prime numbers as lengths tend
to result in good hashing; lengths one less than a power of two are also
good.
Do not try to put symbols in an obarray yourself. This does
not work—only intern can enter a symbol in an obarray properly.
Common Lisp note: In Common Lisp, a single symbol may be interned in several obarrays.
Most of the functions below take a name and sometimes an obarray as
arguments. A wrong-type-argument error is signaled if the name
is not a string, or if the obarray is not a vector.
This function returns the string that is symbol's name. For example:
(symbol-name 'foo) => "foo"Warning: Changing the string by substituting characters does change the name of the symbol, but fails to update the obarray, so don't do it!
This function returns a newly-allocated, uninterned symbol whose name is name (which must be a string). Its value and function definition are void, and its property list is
nil. In the example below, the value ofsymis noteqtofoobecause it is a distinct uninterned symbol whose name is also ‘foo’.(setq sym (make-symbol "foo")) => foo (eq sym 'foo) => nil
This function returns the interned symbol whose name is name. If there is no such symbol in the obarray obarray,
interncreates a new one, adds it to the obarray, and returns it. If obarray is omitted, the value of the global variableobarrayis used.(setq sym (intern "foo")) => foo (eq sym 'foo) => t (setq sym1 (intern "foo" other-obarray)) => foo (eq sym1 'foo) => nil
Common Lisp note: In Common Lisp, you can intern an existing symbol
in an obarray. In Emacs Lisp, you cannot do this, because the argument
to intern must be a string, not a symbol.
This function returns the symbol in obarray whose name is name, or
nilif obarray has no symbol with that name. Therefore, you can useintern-softto test whether a symbol with a given name is already interned. If obarray is omitted, the value of the global variableobarrayis used.The argument name may also be a symbol; in that case, the function returns name if name is interned in the specified obarray, and otherwise
nil.(intern-soft "frazzle") ; No such symbol exists. => nil (make-symbol "frazzle") ; Create an uninterned one. => frazzle (intern-soft "frazzle") ; That one cannot be found. => nil (setq sym (intern "frazzle")) ; Create an interned one. => frazzle (intern-soft "frazzle") ; That one can be found! => frazzle (eq sym 'frazzle) ; And it is the same one. => t
This function calls function once with each symbol in the obarray obarray. Then it returns
nil. If obarray is omitted, it defaults to the value ofobarray, the standard obarray for ordinary symbols.(setq count 0) => 0 (defun count-syms (s) (setq count (1+ count))) => count-syms (mapatoms 'count-syms) => nil count => 1871See
documentationin Accessing Documentation, for another example usingmapatoms.
This function deletes symbol from the obarray obarray. If
symbolis not actually in the obarray,uninterndoes nothing. If obarray isnil, the current obarray is used.If you provide a string instead of a symbol as symbol, it stands for a symbol name. Then
uninterndeletes the symbol (if any) in the obarray which has that name. If there is no such symbol,uninterndoes nothing.If
uninterndoes delete a symbol, it returnst. Otherwise it returnsnil.
A property list (plist for short) is a list of paired elements stored in the property list cell of a symbol. Each of the pairs associates a property name (usually a symbol) with a property or value. Property lists are generally used to record information about a symbol, such as its documentation as a variable, the name of the file where it was defined, or perhaps even the grammatical class of the symbol (representing a word) in a language-understanding system.
Character positions in a string or buffer can also have property lists. See Text Properties.
The property names and values in a property list can be any Lisp
objects, but the names are usually symbols. Property list functions
compare the property names using eq. Here is an example of a
property list, found on the symbol progn when the compiler is
loaded:
(lisp-indent-function 0 byte-compile byte-compile-progn)
Here lisp-indent-function and byte-compile are property
names, and the other two elements are the corresponding values.
Association lists (see Association Lists) are very similar to property lists. In contrast to association lists, the order of the pairs in the property list is not significant since the property names must be distinct.
Property lists are better than association lists for attaching
information to various Lisp function names or variables. If your
program keeps all of its associations in one association list, it will
typically need to search that entire list each time it checks for an
association. This could be slow. By contrast, if you keep the same
information in the property lists of the function names or variables
themselves, each search will scan only the length of one property list,
which is usually short. This is why the documentation for a variable is
recorded in a property named variable-documentation. The byte
compiler likewise uses properties to record those functions needing
special treatment.
However, association lists have their own advantages. Depending on your application, it may be faster to add an association to the front of an association list than to update a property. All properties for a symbol are stored in the same property list, so there is a possibility of a conflict between different uses of a property name. (For this reason, it is a good idea to choose property names that are probably unique, such as by beginning the property name with the program's usual name-prefix for variables and functions.) An association list may be used like a stack where associations are pushed on the front of the list and later discarded; this is not possible with a property list.
This function sets symbol's property list to plist. Normally, plist should be a well-formed property list, but this is not enforced.
(setplist 'foo '(a 1 b (2 3) c nil)) => (a 1 b (2 3) c nil) (symbol-plist 'foo) => (a 1 b (2 3) c nil)For symbols in special obarrays, which are not used for ordinary purposes, it may make sense to use the property list cell in a nonstandard fashion; in fact, the abbrev mechanism does so (see Abbrevs).
This function finds the value of the property named property in symbol's property list. If there is no such property,
nilis returned. Thus, there is no distinction between a value ofniland the absence of the property.The name property is compared with the existing property names using
eq, so any object is a legitimate property.See
putfor an example.
This function puts value onto symbol's property list under the property name property, replacing any previous property value. The
putfunction returns value.(put 'fly 'verb 'transitive) =>'transitive (put 'fly 'noun '(a buzzing little bug)) => (a buzzing little bug) (get 'fly 'verb) => transitive (symbol-plist 'fly) => (verb transitive noun (a buzzing little bug))
These functions are useful for manipulating property lists that are stored in places other than symbols:
This returns the value of the property property stored in the property list plist. For example,
(plist-get '(foo 4) 'foo) => 4
This stores value as the value of the property property in the property list plist. It may modify plist destructively, or it may construct a new list structure without altering the old. The function returns the modified property list, so you can store that back in the place where you got plist. For example,
(setq my-plist '(bar t foo 4)) => (bar t foo 4) (setq my-plist (plist-put my-plist 'foo 69)) => (bar t foo 69) (setq my-plist (plist-put my-plist 'quux '(a))) => (bar t foo 69 quux (a))
You could define put in terms of plist-put as follows:
(defun put (symbol prop value)
(setplist symbol
(plist-put (symbol-plist symbol) prop value)))
This returns non-
nilif plist contains the given property. Unlikeplist-get, this allows you to distinguish between a missing property and a property with the valuenil. The value is actually the tail of plist whosecaris property.
The evaluation of expressions in Emacs Lisp is performed by the
Lisp interpreter—a program that receives a Lisp object as input
and computes its value as an expression. How it does this depends
on the data type of the object, according to rules described in this
chapter. The interpreter runs automatically to evaluate portions of
your program, but can also be called explicitly via the Lisp primitive
function eval.
The Lisp interpreter, or evaluator, is the program that computes the value of an expression that is given to it. When a function written in Lisp is called, the evaluator computes the value of the function by evaluating the expressions in the function body. Thus, running any Lisp program really means running the Lisp interpreter.
How the evaluator handles an object depends primarily on the data type of the object.
A Lisp object that is intended for evaluation is called an expression or a form. The fact that expressions are data objects and not merely text is one of the fundamental differences between Lisp-like languages and typical programming languages. Any object can be evaluated, but in practice only numbers, symbols, lists and strings are evaluated very often.
It is very common to read a Lisp expression and then evaluate the
expression, but reading and evaluation are separate activities, and
either can be performed alone. Reading per se does not evaluate
anything; it converts the printed representation of a Lisp object to the
object itself. It is up to the caller of read whether this
object is a form to be evaluated, or serves some entirely different
purpose. See Input Functions.
Do not confuse evaluation with command key interpretation. The
editor command loop translates keyboard input into a command (an
interactively callable function) using the active keymaps, and then
uses call-interactively to invoke the command. The execution of
the command itself involves evaluation if the command is written in
Lisp, but that is not a part of command key interpretation itself.
See Command Loop.
Evaluation is a recursive process. That is, evaluation of a form may
call eval to evaluate parts of the form. For example, evaluation
of a function call first evaluates each argument of the function call,
and then evaluates each form in the function body. Consider evaluation
of the form (car x): the subform x must first be evaluated
recursively, so that its value can be passed as an argument to the
function car.
Evaluation of a function call ultimately calls the function specified in it. See Functions. The execution of the function may itself work by evaluating the function definition; or the function may be a Lisp primitive implemented in C, or it may be a byte-compiled function (see Byte Compilation).
The evaluation of forms takes place in a context called the environment, which consists of the current values and bindings of all Lisp variables.3 Whenever a form refers to a variable without creating a new binding for it, the value of the variable's binding in the current environment is used. See Variables.
Evaluation of a form may create new environments for recursive
evaluation by binding variables (see Local Variables). These
environments are temporary and vanish by the time evaluation of the form
is complete. The form may also make changes that persist; these changes
are called side effects. An example of a form that produces side
effects is (setq foo 1).
The details of what evaluation means for each kind of form are described below (see Forms).
A Lisp object that is intended to be evaluated is called a form. How Emacs evaluates a form depends on its data type. Emacs has three different kinds of form that are evaluated differently: symbols, lists, and “all other types”. This section describes all three kinds, one by one, starting with the “all other types” which are self-evaluating forms.
A self-evaluating form is any form that is not a list or symbol.
Self-evaluating forms evaluate to themselves: the result of evaluation
is the same object that was evaluated. Thus, the number 25 evaluates to
25, and the string "foo" evaluates to the string "foo".
Likewise, evaluation of a vector does not cause evaluation of the
elements of the vector—it returns the same vector with its contents
unchanged.
'123 ; A number, shown without evaluation. => 123 123 ; Evaluated as usual---result is the same. => 123 (eval '123) ; Evaluated ``by hand''---result is the same. => 123 (eval (eval '123)) ; Evaluating twice changes nothing. => 123
It is common to write numbers, characters, strings, and even vectors in Lisp code, taking advantage of the fact that they self-evaluate. However, it is quite unusual to do this for types that lack a read syntax, because there's no way to write them textually. It is possible to construct Lisp expressions containing these types by means of a Lisp program. Here is an example:
;; Build an expression containing a buffer object. (setq print-exp (list 'print (current-buffer))) => (print #<buffer eval.texi>) ;; Evaluate it. (eval print-exp) -| #<buffer eval.texi> => #<buffer eval.texi>
When a symbol is evaluated, it is treated as a variable. The result is the variable's value, if it has one. If it has none (if its value cell is void), an error is signaled. For more information on the use of variables, see Variables.
In the following example, we set the value of a symbol with
setq. Then we evaluate the symbol, and get back the value that
setq stored.
(setq a 123)
=> 123
(eval 'a)
=> 123
a
=> 123
The symbols nil and t are treated specially, so that the
value of nil is always nil, and the value of t is
always t; you cannot set or bind them to any other values. Thus,
these two symbols act like self-evaluating forms, even though
eval treats them like any other symbol. A symbol whose name
starts with ‘:’ also self-evaluates in the same way; likewise,
its value ordinarily cannot be changed. See Constant Variables.
A form that is a nonempty list is either a function call, a macro call, or a special form, according to its first element. These three kinds of forms are evaluated in different ways, described below. The remaining list elements constitute the arguments for the function, macro, or special form.
The first step in evaluating a nonempty list is to examine its first element. This element alone determines what kind of form the list is and how the rest of the list is to be processed. The first element is not evaluated, as it would be in some Lisp dialects such as Scheme.
If the first element of the list is a symbol then evaluation examines the symbol's function cell, and uses its contents instead of the original symbol. If the contents are another symbol, this process, called symbol function indirection, is repeated until it obtains a non-symbol. See Function Names, for more information about using a symbol as a name for a function stored in the function cell of the symbol.
One possible consequence of this process is an infinite loop, in the
event that a symbol's function cell refers to the same symbol. Or a
symbol may have a void function cell, in which case the subroutine
symbol-function signals a void-function error. But if
neither of these things happens, we eventually obtain a non-symbol,
which ought to be a function or other suitable object.
More precisely, we should now have a Lisp function (a lambda
expression), a byte-code function, a primitive function, a Lisp macro, a
special form, or an autoload object. Each of these types is a case
described in one of the following sections. If the object is not one of
these types, the error invalid-function is signaled.
The following example illustrates the symbol indirection process. We
use fset to set the function cell of a symbol and
symbol-function to get the function cell contents
(see Function Cells). Specifically, we store the symbol car
into the function cell of first, and the symbol first into
the function cell of erste.
;; Build this function cell linkage:
;; ------------- ----- ------- -------
;; | #<subr car> | <-- | car | <-- | first | <-- | erste |
;; ------------- ----- ------- -------
(symbol-function 'car)
=> #<subr car>
(fset 'first 'car)
=> car
(fset 'erste 'first)
=> first
(erste '(1 2 3)) ; Call the function referenced by erste.
=> 1
By contrast, the following example calls a function without any symbol function indirection, because the first element is an anonymous Lisp function, not a symbol.
((lambda (arg) (erste arg))
'(1 2 3))
=> 1
Executing the function itself evaluates its body; this does involve
symbol function indirection when calling erste.
The built-in function indirect-function provides an easy way to
perform symbol function indirection explicitly.
This function returns the meaning of function as a function. If function is a symbol, then it finds function's function definition and starts over with that value. If function is not a symbol, then it returns function itself.
Here is how you could define
indirect-functionin Lisp:(defun indirect-function (function) (if (symbolp function) (indirect-function (symbol-function function)) function))
If the first element of a list being evaluated is a Lisp function
object, byte-code object or primitive function object, then that list is
a function call. For example, here is a call to the function
+:
(+ 1 x)
The first step in evaluating a function call is to evaluate the
remaining elements of the list from left to right. The results are the
actual argument values, one value for each list element. The next step
is to call the function with this list of arguments, effectively using
the function apply (see Calling Functions). If the function
is written in Lisp, the arguments are used to bind the argument
variables of the function (see Lambda Expressions); then the forms
in the function body are evaluated in order, and the value of the last
body form becomes the value of the function call.
If the first element of a list being evaluated is a macro object, then the list is a macro call. When a macro call is evaluated, the elements of the rest of the list are not initially evaluated. Instead, these elements themselves are used as the arguments of the macro. The macro definition computes a replacement form, called the expansion of the macro, to be evaluated in place of the original form. The expansion may be any sort of form: a self-evaluating constant, a symbol, or a list. If the expansion is itself a macro call, this process of expansion repeats until some other sort of form results.
Ordinary evaluation of a macro call finishes by evaluating the expansion. However, the macro expansion is not necessarily evaluated right away, or at all, because other programs also expand macro calls, and they may or may not evaluate the expansions.
Normally, the argument expressions are not evaluated as part of computing the macro expansion, but instead appear as part of the expansion, so they are computed when the expansion is evaluated.
For example, given a macro defined as follows:
(defmacro cadr (x)
(list 'car (list 'cdr x)))
an expression such as (cadr (assq 'handler list)) is a macro
call, and its expansion is:
(car (cdr (assq 'handler list)))
Note that the argument (assq 'handler list) appears in the
expansion.
See Macros, for a complete description of Emacs Lisp macros.
A special form is a primitive function specially marked so that its arguments are not all evaluated. Most special forms define control structures or perform variable bindings—things which functions cannot do.
Each special form has its own rules for which arguments are evaluated and which are used without evaluation. Whether a particular argument is evaluated may depend on the results of evaluating other arguments.
Here is a list, in alphabetical order, of all of the special forms in Emacs Lisp with a reference to where each is described.
andcatchcondcondition-casedefconstdefmacrodefundefvarfunctionifinteractiveletlet*orprog1prog2prognquotesave-current-buffersave-excursionsave-restrictionsave-window-excursionsetqsetq-defaulttrack-mouseunwind-protectwhilewith-output-to-temp-bufferCommon Lisp note: Here are some comparisons of special forms in GNU Emacs Lisp and Common Lisp.setq,if, andcatchare special forms in both Emacs Lisp and Common Lisp.defunis a special form in Emacs Lisp, but a macro in Common Lisp.save-excursionis a special form in Emacs Lisp, but doesn't exist in Common Lisp.throwis a special form in Common Lisp (because it must be able to throw multiple values), but it is a function in Emacs Lisp (which doesn't have multiple values).
The autoload feature allows you to call a function or macro whose function definition has not yet been loaded into Emacs. It specifies which file contains the definition. When an autoload object appears as a symbol's function definition, calling that symbol as a function automatically loads the specified file; then it calls the real definition loaded from that file. See Autoload.
The special form quote returns its single argument, as written,
without evaluating it. This provides a way to include constant symbols
and lists, which are not self-evaluating objects, in a program. (It is
not necessary to quote self-evaluating objects such as numbers, strings,
and vectors.)
Because quote is used so often in programs, Lisp provides a
convenient read syntax for it. An apostrophe character (‘'’)
followed by a Lisp object (in read syntax) expands to a list whose first
element is quote, and whose second element is the object. Thus,
the read syntax 'x is an abbreviation for (quote x).
Here are some examples of expressions that use quote:
(quote (+ 1 2))
=> (+ 1 2)
(quote foo)
=> foo
'foo
=> foo
''foo
=> (quote foo)
'(quote foo)
=> (quote foo)
['foo]
=> [(quote foo)]
Other quoting constructs include function (see Anonymous Functions), which causes an anonymous lambda expression written in Lisp
to be compiled, and ‘`’ (see Backquote), which is used to quote
only part of a list, while computing and substituting other parts.
Most often, forms are evaluated automatically, by virtue of their
occurrence in a program being run. On rare occasions, you may need to
write code that evaluates a form that is computed at run time, such as
after reading a form from text being edited or getting one from a
property list. On these occasions, use the eval function.
The functions and variables described in this section evaluate forms, specify limits to the evaluation process, or record recently returned values. Loading a file also does evaluation (see Loading).
Note: it is generally cleaner and more flexible to store a
function in a data structure, and call it with funcall or
apply, than to store an expression in the data structure and
evaluate it. Using functions provides the ability to pass information
to them as arguments.
This is the basic function evaluating an expression. It evaluates form in the current environment and returns the result. How the evaluation proceeds depends on the type of the object (see Forms).
Since
evalis a function, the argument expression that appears in a call toevalis evaluated twice: once as preparation beforeevalis called, and again by theevalfunction itself. Here is an example:(setq foo 'bar) => bar (setq bar 'baz) => baz ;; Hereevalreceives argumentfoo(eval 'foo) => bar ;; Hereevalreceives argumentbar, which is the value offoo(eval foo) => bazThe number of currently active calls to
evalis limited tomax-lisp-eval-depth(see below).
This function evaluates the forms in the current buffer in the region defined by the positions start and end. It reads forms from the region and calls
evalon them until the end of the region is reached, or until an error is signaled and not handled.If stream is non-
nil, the values that result from evaluating the expressions in the region are printed using stream. See Output Streams.If read-function is non-
nil, it should be a function, which is used instead ofreadto read expressions one by one. This function is called with one argument, the stream for reading input. You can also use the variableload-read-function(see How Programs Do Loading) to specify this function, but it is more robust to use the read-function argument.
eval-regionalways returnsnil.
This is like
eval-regionexcept that it operates on the whole buffer.
This variable defines the maximum depth allowed in calls to
eval,apply, andfuncallbefore an error is signaled (with error message"Lisp nesting exceeds max-lisp-eval-depth"). This limit, with the associated error when it is exceeded, is one way that Lisp avoids infinite recursion on an ill-defined function. The depth limit counts internal uses ofeval,apply, andfuncall, such as for calling the functions mentioned in Lisp expressions, and recursive evaluation of function call arguments and function body forms, as well as explicit calls in Lisp code.The default value of this variable is 300. If you set it to a value less than 100, Lisp will reset it to 100 if the given value is reached. Entry to the Lisp debugger increases the value, if there is little room left, to make sure the debugger itself has room to execute.
max-specpdl-sizeprovides another limit on nesting. See Local Variables.
The value of this variable is a list of the values returned by all the expressions that were read, evaluated, and printed from buffers (including the minibuffer) by the standard Emacs commands which do this. The elements are ordered most recent first.
(setq x 1) => 1 (list 'A (1+ 2) auto-save-default) => (A 3 t) values => ((A 3 t) 1 ...)This variable is useful for referring back to values of forms recently evaluated. It is generally a bad idea to print the value of
valuesitself, since this may be very long. Instead, examine particular elements, like this:;; Refer to the most recent evaluation result. (nth 0 values) => (A 3 t) ;; That put a new element on, ;; so all elements move back one. (nth 1 values) => (A 3 t) ;; This gets the element that was next-to-most-recent ;; before this example. (nth 3 values) => 1
A Lisp program consists of expressions or forms (see Forms). We control the order of execution of these forms by enclosing them in control structures. Control structures are special forms which control when, whether, or how many times to execute the forms they contain.
The simplest order of execution is sequential execution: first form a, then form b, and so on. This is what happens when you write several forms in succession in the body of a function, or at top level in a file of Lisp code—the forms are executed in the order written. We call this textual order. For example, if a function body consists of two forms a and b, evaluation of the function evaluates first a and then b. The result of evaluating b becomes the value of the function.
Explicit control structures make possible an order of execution other than sequential.
Emacs Lisp provides several kinds of control structure, including other varieties of sequencing, conditionals, iteration, and (controlled) jumps—all discussed below. The built-in control structures are special forms since their subforms are not necessarily evaluated or not evaluated sequentially. You can use macros to define your own control structure constructs (see Macros).
Evaluating forms in the order they appear is the most common way
control passes from one form to another. In some contexts, such as in a
function body, this happens automatically. Elsewhere you must use a
control structure construct to do this: progn, the simplest
control construct of Lisp.
A progn special form looks like this:
(progn a b c ...)
and it says to execute the forms a, b, c, and so on, in
that order. These forms are called the body of the progn form.
The value of the last form in the body becomes the value of the entire
progn. (progn) returns nil.
In the early days of Lisp, progn was the only way to execute
two or more forms in succession and use the value of the last of them.
But programmers found they often needed to use a progn in the
body of a function, where (at that time) only one form was allowed. So
the body of a function was made into an “implicit progn”:
several forms are allowed just as in the body of an actual progn.
Many other control structures likewise contain an implicit progn.
As a result, progn is not used as much as it was many years ago.
It is needed now most often inside an unwind-protect, and,
or, or in the then-part of an if.
This special form evaluates all of the forms, in textual order, returning the result of the final form.
(progn (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" => "The third form"
Two other control constructs likewise evaluate a series of forms but return a different value:
This special form evaluates form1 and all of the forms, in textual order, returning the result of form1.
(prog1 (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" => "The first form"Here is a way to remove the first element from a list in the variable
x, then return the value of that former element:(prog1 (car x) (setq x (cdr x)))
This special form evaluates form1, form2, and all of the following forms, in textual order, returning the result of form2.
(prog2 (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" => "The second form"
Conditional control structures choose among alternatives. Emacs Lisp
has four conditional forms: if, which is much the same as in
other languages; when and unless, which are variants of
if; and cond, which is a generalized case statement.
ifchooses between the then-form and the else-forms based on the value of condition. If the evaluated condition is non-nil, then-form is evaluated and the result returned. Otherwise, the else-forms are evaluated in textual order, and the value of the last one is returned. (The else part ofifis an example of an implicitprogn. See Sequencing.)If condition has the value
nil, and no else-forms are given,ifreturnsnil.
ifis a special form because the branch that is not selected is never evaluated—it is ignored. Thus, in the example below,trueis not printed because(if nil (print 'true) 'very-false) => very-false
This is a variant of
ifwhere there are no else-forms, and possibly several then-forms. In particular,(when condition a b c)is entirely equivalent to
(if condition (progn a b c) nil)
This is a variant of
ifwhere there is no then-form:(unless condition a b c)is entirely equivalent to
(if condition nil a b c)
condchooses among an arbitrary number of alternatives. Each clause in thecondmust be a list. The car of this list is the condition; the remaining elements, if any, the body-forms. Thus, a clause looks like this:(condition body-forms...)
condtries the clauses in textual order, by evaluating the condition of each clause. If the value of condition is non-nil, the clause “succeeds”; thencondevaluates its body-forms, and the value of the last of body-forms becomes the value of thecond. The remaining clauses are ignored.If the value of condition is
nil, the clause “fails”, so thecondmoves on to the following clause, trying its condition.If every condition evaluates to
nil, so that every clause fails,condreturnsnil.A clause may also look like this:
(condition)Then, if condition is non-
nilwhen tested, the value of condition becomes the value of thecondform.The following example has four clauses, which test for the cases where the value of
xis a number, string, buffer and symbol, respectively:(cond ((numberp x) x) ((stringp x) x) ((bufferp x) (setq temporary-hack x) ; multiple body-forms (buffer-name x)) ; in one clause ((symbolp x) (symbol-value x)))Often we want to execute the last clause whenever none of the previous clauses was successful. To do this, we use
tas the condition of the last clause, like this:(tbody-forms). The formtevaluates tot, which is nevernil, so this clause never fails, provided thecondgets to it at all.For example,
(setq a 5) (cond ((eq a 'hack) 'foo) (t "default")) => "default"This
condexpression returnsfooif the value ofaishack, and returns the string"default"otherwise.
Any conditional construct can be expressed with cond or with
if. Therefore, the choice between them is a matter of style.
For example:
(if a b c)
==
(cond (a b) (t c))
This section describes three constructs that are often used together
with if and cond to express complicated conditions. The
constructs and and or can also be used individually as
kinds of multiple conditional constructs.
This function tests for the falsehood of condition. It returns
tif condition isnil, andnilotherwise. The functionnotis identical tonull, and we recommend using the namenullif you are testing for an empty list.
The
andspecial form tests whether all the conditions are true. It works by evaluating the conditions one by one in the order written.If any of the conditions evaluates to
nil, then the result of theandmust benilregardless of the remaining conditions; soandreturnsnilright away, ignoring the remaining conditions.If all the conditions turn out non-
nil, then the value of the last of them becomes the value of theandform. Just(and), with no conditions, returnst, appropriate because all the conditions turned out non-nil. (Think about it; which one did not?)Here is an example. The first condition returns the integer 1, which is not
nil. Similarly, the second condition returns the integer 2, which is notnil. The third condition isnil, so the remaining condition is never evaluated.(and (print 1) (print 2) nil (print 3)) -| 1 -| 2 => nilHere is a more realistic example of using
and:(if (and (consp foo) (eq (car foo) 'x)) (message "foo is a list starting with x"))Note that
(car foo)is not executed if(consp foo)returnsnil, thus avoiding an error.
andcan be expressed in terms of eitheriforcond. For example:(and arg1 arg2 arg3) == (if arg1 (if arg2 arg3)) == (cond (arg1 (cond (arg2 arg3))))
The
orspecial form tests whether at least one of the conditions is true. It works by evaluating all the conditions one by one in the order written.If any of the conditions evaluates to a non-
nilvalue, then the result of theormust be non-nil; soorreturns right away, ignoring the remaining conditions. The value it returns is the non-nilvalue of the condition just evaluated.If all the conditions turn out
nil, then theorexpression returnsnil. Just(or), with no conditions, returnsnil, appropriate because all the conditions turned outnil. (Think about it; which one did not?)For example, this expression tests whether
xis eithernilor the integer zero:(or (eq x nil) (eq x 0))Like the
andconstruct,orcan be written in terms ofcond. For example:(or arg1 arg2 arg3) == (cond (arg1) (arg2) (arg3))You could almost write
orin terms ofif, but not quite:(if arg1 arg1 (if arg2 arg2 arg3))This is not completely equivalent because it can evaluate arg1 or arg2 twice. By contrast,
(orarg1 arg2 arg3)never evaluates any argument more than once.
Iteration means executing part of a program repetitively. For
example, you might want to repeat some computation once for each element
of a list, or once for each integer from 0 to n. You can do this
in Emacs Lisp with the special form while:
whilefirst evaluates condition. If the result is non-nil, it evaluates forms in textual order. Then it reevaluates condition, and if the result is non-nil, it evaluates forms again. This process repeats until condition evaluates tonil.There is no limit on the number of iterations that may occur. The loop will continue until either condition evaluates to
nilor until an error orthrowjumps out of it (see Nonlocal Exits).The value of a
whileform is alwaysnil.(setq num 0) => 0 (while (< num 4) (princ (format "Iteration %d." num)) (setq num (1+ num))) -| Iteration 0. -| Iteration 1. -| Iteration 2. -| Iteration 3. => nilTo write a “repeat...until” loop, which will execute something on each iteration and then do the end-test, put the body followed by the end-test in a
prognas the first argument ofwhile, as shown here:(while (progn (forward-line 1) (not (looking-at "^$"))))This moves forward one line and continues moving by lines until it reaches an empty line. It is peculiar in that the
whilehas no body, just the end test (which also does the real work of moving point).
The dolist and dotimes macros provide convenient ways to
write two common kinds of loops.
This construct executes body once for each element of list, using the variable var to hold the current element. Then it returns the value of evaluating result, or
nilif result is omitted. For example, here is how you could usedolistto define thereversefunction:(defun reverse (list) (let (value) (dolist (elt list value) (setq value (cons elt value)))))
This construct executes body once for each integer from 0 (inclusive) to count (exclusive), using the variable var to hold the integer for the current iteration. Then it returns the value of evaluating result, or
nilif result is omitted. Here is an example of usingdotimesdo something 100 times:(dotimes (i 100) (insert "I will not obey absurd orders\n"))
A nonlocal exit is a transfer of control from one point in a program to another remote point. Nonlocal exits can occur in Emacs Lisp as a result of errors; you can also use them under explicit control. Nonlocal exits unbind all variable bindings made by the constructs being exited.
catch and throwMost control constructs affect only the flow of control within the
construct itself. The function throw is the exception to this
rule of normal program execution: it performs a nonlocal exit on
request. (There are other exceptions, but they are for error handling
only.) throw is used inside a catch, and jumps back to
that catch. For example:
(defun foo-outer ()
(catch 'foo
(foo-inner)))
(defun foo-inner ()
...
(if x
(throw 'foo t))
...)
The throw form, if executed, transfers control straight back to
the corresponding catch, which returns immediately. The code
following the throw is not executed. The second argument of
throw is used as the return value of the catch.
The function throw finds the matching catch based on the
first argument: it searches for a catch whose first argument is
eq to the one specified in the throw. If there is more
than one applicable catch, the innermost one takes precedence.
Thus, in the above example, the throw specifies foo, and
the catch in foo-outer specifies the same symbol, so that
catch is the applicable one (assuming there is no other matching
catch in between).
Executing throw exits all Lisp constructs up to the matching
catch, including function calls. When binding constructs such as
let or function calls are exited in this way, the bindings are
unbound, just as they are when these constructs exit normally
(see Local Variables). Likewise, throw restores the buffer
and position saved by save-excursion (see Excursions), and
the narrowing status saved by save-restriction and the window
selection saved by save-window-excursion (see Window Configurations). It also runs any cleanups established with the
unwind-protect special form when it exits that form
(see Cleanups).
The throw need not appear lexically within the catch
that it jumps to. It can equally well be called from another function
called within the catch. As long as the throw takes place
chronologically after entry to the catch, and chronologically
before exit from it, it has access to that catch. This is why
throw can be used in commands such as exit-recursive-edit
that throw back to the editor command loop (see Recursive Editing).
Common Lisp note: Most other versions of Lisp, including Common Lisp, have several ways of transferring control nonsequentially:return,return-from, andgo, for example. Emacs Lisp has onlythrow.
catchestablishes a return point for thethrowfunction. The return point is distinguished from other such return points by tag, which may be any Lisp object exceptnil. The argument tag is evaluated normally before the return point is established.With the return point in effect,
catchevaluates the forms of the body in textual order. If the forms execute normally (without error or nonlocal exit) the value of the last body form is returned from thecatch.If a
throwis executed during the execution of body, specifying the same value tag, thecatchform exits immediately; the value it returns is whatever was specified as the second argument ofthrow.
The purpose of
throwis to return from a return point previously established withcatch. The argument tag is used to choose among the various existing return points; it must beeqto the value specified in thecatch. If multiple return points match tag, the innermost one is used.The argument value is used as the value to return from that
catch.If no return point is in effect with tag tag, then a
no-catcherror is signaled with data(tag value).
catch and throwOne way to use catch and throw is to exit from a doubly
nested loop. (In most languages, this would be done with a “go to”.)
Here we compute (foo i j) for i and j
varying from 0 to 9:
(defun search-foo ()
(catch 'loop
(let ((i 0))
(while (< i 10)
(let ((j 0))
(while (< j 10)
(if (foo i j)
(throw 'loop (list i j)))
(setq j (1+ j))))
(setq i (1+ i))))))
If foo ever returns non-nil, we stop immediately and return a
list of i and j. If foo always returns nil, the
catch returns normally, and the value is nil, since that
is the result of the while.
Here are two tricky examples, slightly different, showing two
return points at once. First, two return points with the same tag,
hack:
(defun catch2 (tag)
(catch tag
(throw 'hack 'yes)))
=> catch2
(catch 'hack
(print (catch2 'hack))
'no)
-| yes
=> no
Since both return points have tags that match the throw, it goes to
the inner one, the one established in catch2. Therefore,
catch2 returns normally with value yes, and this value is
printed. Finally the second body form in the outer catch, which is
'no, is evaluated and returned from the outer catch.
Now let's change the argument given to catch2:
(catch 'hack
(print (catch2 'quux))
'no)
=> yes
We still have two return points, but this time only the outer one has
the tag hack; the inner one has the tag quux instead.
Therefore, throw makes the outer catch return the value
yes. The function print is never called, and the
body-form 'no is never evaluated.
When Emacs Lisp attempts to evaluate a form that, for some reason, cannot be evaluated, it signals an error.
When an error is signaled, Emacs's default reaction is to print an error message and terminate execution of the current command. This is the right thing to do in most cases, such as if you type C-f at the end of the buffer.
In complicated programs, simple termination may not be what you want.
For example, the program may have made temporary changes in data
structures, or created temporary buffers that should be deleted before
the program is finished. In such cases, you would use
unwind-protect to establish cleanup expressions to be
evaluated in case of error. (See Cleanups.) Occasionally, you may
wish the program to continue execution despite an error in a subroutine.
In these cases, you would use condition-case to establish
error handlers to recover control in case of error.
Resist the temptation to use error handling to transfer control from
one part of the program to another; use catch and throw
instead. See Catch and Throw.
Most errors are signaled “automatically” within Lisp primitives
which you call for other purposes, such as if you try to take the
car of an integer or move forward a character at the end of the
buffer. You can also signal errors explicitly with the functions
error and signal.
Quitting, which happens when the user types C-g, is not considered an error, but it is handled almost like an error. See Quitting.
The error message should state what is wrong (“File does not exist”), not how things ought to be (“File must exist”). The convention in Emacs Lisp is that error messages should start with a capital letter, but should not end with any sort of punctuation.
This function signals an error with an error message constructed by applying
format(see String Conversion) to format-string and args.These examples show typical uses of
error:(error "That is an error -- try something else") error--> That is an error -- try something else (error "You have committed %d errors" 10) error--> You have committed 10 errors
errorworks by callingsignalwith two arguments: the error symbolerror, and a list containing the string returned byformat.Warning: If you want to use your own string as an error message verbatim, don't just write
(errorstring). If string contains ‘%’, it will be interpreted as a format specifier, with undesirable results. Instead, use(error "%s"string).
This function signals an error named by error-symbol. The argument data is a list of additional Lisp objects relevant to the circumstances of the error.
The argument error-symbol must be an error symbol—a symbol bearing a property
error-conditionswhose value is a list of condition names. This is how Emacs Lisp classifies different sorts of errors.The number and significance of the objects in data depends on error-symbol. For example, with a
wrong-type-argerror, there should be two objects in the list: a predicate that describes the type that was expected, and the object that failed to fit that type. See Error Symbols, for a description of error symbols.Both error-symbol and data are available to any error handlers that handle the error:
condition-casebinds a local variable to a list of the form(error-symbol.data)(see Handling Errors). If the error is not handled, these two values are used in printing the error message.The function
signalnever returns (though in older Emacs versions it could sometimes return).(signal 'wrong-number-of-arguments '(x y)) error--> Wrong number of arguments: x, y (signal 'no-such-error '("My unknown error condition")) error--> peculiar error: "My unknown error condition"
Common Lisp note: Emacs Lisp has nothing like the Common Lisp concept of continuable errors.
When an error is signaled, signal searches for an active
handler for the error. A handler is a sequence of Lisp
expressions designated to be executed if an error happens in part of the
Lisp program. If the error has an applicable handler, the handler is
executed, and control resumes following the handler. The handler
executes in the environment of the condition-case that
established it; all functions called within that condition-case
have already been exited, and the handler cannot return to them.
If there is no applicable handler for the error, the current command is terminated and control returns to the editor command loop, because the command loop has an implicit handler for all kinds of errors. The command loop's handler uses the error symbol and associated data to print an error message.
An error that has no explicit handler may call the Lisp debugger. The
debugger is enabled if the variable debug-on-error (see Error Debugging) is non-nil. Unlike error handlers, the debugger runs
in the environment of the error, so that you can examine values of
variables precisely as they were at the time of the error.
The usual effect of signaling an error is to terminate the command
that is running and return immediately to the Emacs editor command loop.
You can arrange to trap errors occurring in a part of your program by
establishing an error handler, with the special form
condition-case. A simple example looks like this:
(condition-case nil
(delete-file filename)
(error nil))
This deletes the file named filename, catching any error and
returning nil if an error occurs.
The second argument of condition-case is called the
protected form. (In the example above, the protected form is a
call to delete-file.) The error handlers go into effect when
this form begins execution and are deactivated when this form returns.
They remain in effect for all the intervening time. In particular, they
are in effect during the execution of functions called by this form, in
their subroutines, and so on. This is a good thing, since, strictly
speaking, errors can be signaled only by Lisp primitives (including
signal and error) called by the protected form, not by the
protected form itself.
The arguments after the protected form are handlers. Each handler
lists one or more condition names (which are symbols) to specify
which errors it will handle. The error symbol specified when an error
is signaled also defines a list of condition names. A handler applies
to an error if they have any condition names in common. In the example
above, there is one handler, and it specifies one condition name,
error, which covers all errors.
The search for an applicable handler checks all the established handlers
starting with the most recently established one. Thus, if two nested
condition-case forms offer to handle the same error, the inner of
the two gets to handle it.
If an error is handled by some condition-case form, this
ordinarily prevents the debugger from being run, even if
debug-on-error says this error should invoke the debugger.
See Error Debugging. If you want to be able to debug errors that are
caught by a condition-case, set the variable
debug-on-signal to a non-nil value.
When an error is handled, control returns to the handler. Before this
happens, Emacs unbinds all variable bindings made by binding constructs
that are being exited and executes the cleanups of all
unwind-protect forms that are exited. Once control arrives at
the handler, the body of the handler is executed.
After execution of the handler body, execution returns from the
condition-case form. Because the protected form is exited
completely before execution of the handler, the handler cannot resume
execution at the point of the error, nor can it examine variable
bindings that were made within the protected form. All it can do is
clean up and proceed.
The condition-case construct is often used to trap errors that
are predictable, such as failure to open a file in a call to
insert-file-contents. It is also used to trap errors that are
totally unpredictable, such as when the program evaluates an expression
read from the user.
Error signaling and handling have some resemblance to throw and
catch (see Catch and Throw), but they are entirely separate
facilities. An error cannot be caught by a catch, and a
throw cannot be handled by an error handler (though using
throw when there is no suitable catch signals an error
that can be handled).
This special form establishes the error handlers handlers around the execution of protected-form. If protected-form executes without error, the value it returns becomes the value of the
condition-caseform; in this case, thecondition-casehas no effect. Thecondition-caseform makes a difference when an error occurs during protected-form.Each of the handlers is a list of the form
(conditions body...). Here conditions is an error condition name to be handled, or a list of condition names; body is one or more Lisp expressions to be executed when this handler handles an error. Here are examples of handlers:(error nil) (arith-error (message "Division by zero")) ((arith-error file-error) (message "Either division by zero or failure to open a file"))Each error that occurs has an error symbol that describes what kind of error it is. The
error-conditionsproperty of this symbol is a list of condition names (see Error Symbols). Emacs searches all the activecondition-caseforms for a handler that specifies one or more of these condition names; the innermost matchingcondition-casehandles the error. Within thiscondition-case, the first applicable handler handles the error.After executing the body of the handler, the
condition-casereturns normally, using the value of the last form in the handler body as the overall value.The argument var is a variable.
condition-casedoes not bind this variable when executing the protected-form, only when it handles an error. At that time, it binds var locally to an error description, which is a list giving the particulars of the error. The error description has the form(error-symbol.data). The handler can refer to this list to decide what to do. For example, if the error is for failure opening a file, the file name is the second element of data—the third element of the error description.If var is
nil, that means no variable is bound. Then the error symbol and associated data are not available to the handler.
This function returns the error message string for a given error descriptor. It is useful if you want to handle an error by printing the usual error message for that error.
Here is an example of using condition-case to handle the error
that results from dividing by zero. The handler displays the error
message (but without a beep), then returns a very large number.
(defun safe-divide (dividend divisor)
(condition-case err
;; Protected form.
(/ dividend divisor)
;; The handler.
(arith-error ; Condition.
;; Display the usual message for this error.
(message "%s" (error-message-string err))
1000000)))
=> safe-divide
(safe-divide 5 0)
-| Arithmetic error: (arith-error)
=> 1000000
The handler specifies condition name arith-error so that it will handle only division-by-zero errors. Other kinds of errors will not be handled, at least not by this condition-case. Thus,
(safe-divide nil 3)
error--> Wrong type argument: number-or-marker-p, nil
Here is a condition-case that catches all kinds of errors,
including those signaled with error:
(setq baz 34)
=> 34
(condition-case err
(if (eq baz 35)
t
;; This is a call to the function error.
(error "Rats! The variable %s was %s, not 35" 'baz baz))
;; This is the handler; it is not a form.
(error (princ (format "The error was: %s" err))
2))
-| The error was: (error "Rats! The variable baz was 34, not 35")
=> 2
When you signal an error, you specify an error symbol to specify the kind of error you have in mind. Each error has one and only one error symbol to categorize it. This is the finest classification of errors defined by the Emacs Lisp language.
These narrow classifications are grouped into a hierarchy of wider
classes called error conditions, identified by condition
names. The narrowest such classes belong to the error symbols
themselves: each error symbol is also a condition name. There are also
condition names for more extensive classes, up to the condition name
error which takes in all kinds of errors. Thus, each error has
one or more condition names: error, the error symbol if that
is distinct from error, and perhaps some intermediate
classifications.
In order for a symbol to be an error symbol, it must have an
error-conditions property which gives a list of condition names.
This list defines the conditions that this kind of error belongs to.
(The error symbol itself, and the symbol error, should always be
members of this list.) Thus, the hierarchy of condition names is
defined by the error-conditions properties of the error symbols.
In addition to the error-conditions list, the error symbol
should have an error-message property whose value is a string to
be printed when that error is signaled but not handled. If the
error-message property exists, but is not a string, the error
message ‘peculiar error’ is used.
Here is how we define a new error symbol, new-error:
(put 'new-error
'error-conditions
'(error my-own-errors new-error))
=> (error my-own-errors new-error)
(put 'new-error 'error-message "A new error")
=> "A new error"
This error has three condition names: new-error, the narrowest
classification; my-own-errors, which we imagine is a wider
classification; and error, which is the widest of all.
The error string should start with a capital letter but it should not end with a period. This is for consistency with the rest of Emacs.
Naturally, Emacs will never signal new-error on its own; only
an explicit call to signal (see Signaling Errors) in your
code can do this:
(signal 'new-error '(x y))
error--> A new error: x, y
This error can be handled through any of the three condition names.
This example handles new-error and any other errors in the class
my-own-errors:
(condition-case foo
(bar nil t)
(my-own-errors nil))
The significant way that errors are classified is by their condition
names—the names used to match errors with handlers. An error symbol
serves only as a convenient way to specify the intended error message
and list of condition names. It would be cumbersome to give
signal a list of condition names rather than one error symbol.
By contrast, using only error symbols without condition names would
seriously decrease the power of condition-case. Condition names
make it possible to categorize errors at various levels of generality
when you write an error handler. Using error symbols alone would
eliminate all but the narrowest level of classification.
See Standard Errors, for a list of all the standard error symbols and their conditions.
The unwind-protect construct is essential whenever you
temporarily put a data structure in an inconsistent state; it permits
you to make the data consistent again in the event of an error or throw.
unwind-protectexecutes the body with a guarantee that the cleanup-forms will be evaluated if control leaves body, no matter how that happens. The body may complete normally, or execute athrowout of theunwind-protect, or cause an error; in all cases, the cleanup-forms will be evaluated.If the body forms finish normally,
unwind-protectreturns the value of the last body form, after it evaluates the cleanup-forms. If the body forms do not finish,unwind-protectdoes not return any value in the normal sense.Only the body is protected by the
unwind-protect. If any of the cleanup-forms themselves exits nonlocally (via athrowor an error),unwind-protectis not guaranteed to evaluate the rest of them. If the failure of one of the cleanup-forms has the potential to cause trouble, then protect it with anotherunwind-protectaround that form.The number of currently active
unwind-protectforms counts, together with the number of local variable bindings, against the limitmax-specpdl-size(see Local Variables).
For example, here we make an invisible buffer for temporary use, and make sure to kill it before finishing:
(save-excursion
(let ((buffer (get-buffer-create " *temp*")))
(set-buffer buffer)
(unwind-protect
body
(kill-buffer buffer))))
You might think that we could just as well write (kill-buffer
(current-buffer)) and dispense with the variable buffer.
However, the way shown above is safer, if body happens to get an
error after switching to a different buffer! (Alternatively, you could
write another save-excursion around the body, to ensure that the
temporary buffer becomes current again in time to kill it.)
Emacs includes a standard macro called with-temp-buffer which
expands into more or less the code shown above (see Current Buffer).
Several of the macros defined in this manual use unwind-protect
in this way.
Here is an actual example derived from an FTP package. It creates a
process (see Processes) to try to establish a connection to a remote
machine. As the function ftp-login is highly susceptible to
numerous problems that the writer of the function cannot anticipate, it
is protected with a form that guarantees deletion of the process in the
event of failure. Otherwise, Emacs might fill up with useless
subprocesses.
(let ((win nil))
(unwind-protect
(progn
(setq process (ftp-setup-buffer host file))
(if (setq win (ftp-login process host user password))
(message "Logged in")
(error "Ftp login failed")))
(or win (and process (delete-process process)))))
This example has a small bug: if the user types C-g to
quit, and the quit happens immediately after the function
ftp-setup-buffer returns but before the variable process is
set, the process will not be killed. There is no easy way to fix this bug,
but at least it is very unlikely.
A variable is a name used in a program to stand for a value. Nearly all programming languages have variables of some sort. In the text of a Lisp program, variables are written using the syntax for symbols.
In Lisp, unlike most programming languages, programs are represented primarily as Lisp objects and only secondarily as text. The Lisp objects used for variables are symbols: the symbol name is the variable name, and the variable's value is stored in the value cell of the symbol. The use of a symbol as a variable is independent of its use as a function name. See Symbol Components.
The Lisp objects that constitute a Lisp program determine the textual form of the program—it is simply the read syntax for those Lisp objects. This is why, for example, a variable in a textual Lisp program is written using the read syntax for the symbol that represents the variable.
The simplest way to use a variable is globally. This means that the variable has just one value at a time, and this value is in effect (at least for the moment) throughout the Lisp system. The value remains in effect until you specify a new one. When a new value replaces the old one, no trace of the old value remains in the variable.
You specify a value for a symbol with setq. For example,
(setq x '(a b))
gives the variable x the value (a b). Note that
setq does not evaluate its first argument, the name of the
variable, but it does evaluate the second argument, the new value.
Once the variable has a value, you can refer to it by using the symbol by itself as an expression. Thus,
x => (a b)
assuming the setq form shown above has already been executed.
If you do set the same variable again, the new value replaces the old one:
x
=> (a b)
(setq x 4)
=> 4
x
=> 4
In Emacs Lisp, certain symbols normally evaluate to themselves. These
include nil and t, as well as any symbol whose name starts
with ‘:’ (these are called keywords). These symbols cannot
be rebound, nor can their values be changed. Any attempt to set or bind
nil or t signals a setting-constant error. The
same is true for a keyword (a symbol whose name starts with ‘:’),
if it is interned in the standard obarray, except that setting such a
symbol to itself is not an error.
nil == 'nil
=> nil
(setq nil 500)
error--> Attempt to set constant symbol: nil
function returns
tif object is a symbol whose name starts with ‘:’, interned in the standard obarray, and returnsnilotherwise.
Global variables have values that last until explicitly superseded with new values. Sometimes it is useful to create variable values that exist temporarily—only until a certain part of the program finishes. These values are called local, and the variables so used are called local variables.
For example, when a function is called, its argument variables receive
new local values that last until the function exits. The let
special form explicitly establishes new local values for specified
variables; these last until exit from the let form.
Establishing a local value saves away the previous value (or lack of one) of the variable. When the life span of the local value is over, the previous value is restored. In the mean time, we say that the previous value is shadowed and not visible. Both global and local values may be shadowed (see Scope).
If you set a variable (such as with setq) while it is local,
this replaces the local value; it does not alter the global value, or
previous local values, that are shadowed. To model this behavior, we
speak of a local binding of the variable as well as a local value.
The local binding is a conceptual place that holds a local value.
Entry to a function, or a special form such as let, creates the
local binding; exit from the function or from the let removes the
local binding. As long as the local binding lasts, the variable's value
is stored within it. Use of setq or set while there is a
local binding stores a different value into the local binding; it does
not create a new binding.
We also speak of the global binding, which is where (conceptually) the global value is kept.
A variable can have more than one local binding at a time (for
example, if there are nested let forms that bind it). In such a
case, the most recently created local binding that still exists is the
current binding of the variable. (This rule is called
dynamic scoping; see Variable Scoping.) If there are no
local bindings, the variable's global binding is its current binding.
We sometimes call the current binding the most-local existing
binding, for emphasis. Ordinary evaluation of a symbol always returns
the value of its current binding.
The special forms let and let* exist to create
local bindings.
This special form binds variables according to bindings and then evaluates all of the forms in textual order. The
let-form returns the value of the last form in forms.Each of the bindings is either (i) a symbol, in which case that symbol is bound to
nil; or (ii) a list of the form(symbol value-form), in which case symbol is bound to the result of evaluating value-form. If value-form is omitted,nilis used.All of the value-forms in bindings are evaluated in the order they appear and before binding any of the symbols to them. Here is an example of this:
Zis bound to the old value ofY, which is 2, not the new value ofY, which is 1.(setq Y 2) => 2 (let ((Y 1) (Z Y)) (list Y Z)) => (1 2)
This special form is like
let, but it binds each variable right after computing its local value, before computing the local value for the next variable. Therefore, an expression in bindings can reasonably refer to the preceding symbols bound in thislet*form. Compare the following example with the example above forlet.(setq Y 2) => 2 (let* ((Y 1) (Z Y)) ; Use the just-established value ofY. (list Y Z)) => (1 1)
Here is a complete list of the other facilities that create local bindings:
Variables can also have buffer-local bindings (see Buffer-Local Variables) and frame-local bindings (see Frame-Local Variables); a few variables have terminal-local bindings (see Multiple Displays). These kinds of bindings work somewhat like ordinary local bindings, but they are localized depending on “where” you are in Emacs, rather than localized in time.
This variable defines the limit on the total number of local variable bindings and
unwind-protectcleanups (see Nonlocal Exits) that are allowed before signaling an error (with data"Variable binding depth exceeds max-specpdl-size").This limit, with the associated error when it is exceeded, is one way that Lisp avoids infinite recursion on an ill-defined function.
max-lisp-eval-depthprovides another limit on depth of nesting. See Eval.The default value is 600. Entry to the Lisp debugger increases the value, if there is little room left, to make sure the debugger itself has room to execute.
If you have never given a symbol any value as a global variable, we
say that that symbol's global value is void. In other words, the
symbol's value cell does not have any Lisp object in it. If you try to
evaluate the symbol, you get a void-variable error rather than
a value.
Note that a value of nil is not the same as void. The symbol
nil is a Lisp object and can be the value of a variable just as any
other object can be; but it is a value. A void variable does not
have any value.
After you have given a variable a value, you can make it void once more
using makunbound.
This function makes the current variable binding of symbol void. Subsequent attempts to use this symbol's value as a variable will signal the error
void-variable, unless and until you set it again.
makunboundreturns symbol.(makunbound 'x) ; Make the global value ofxvoid. => x x error--> Symbol's value as variable is void: xIf symbol is locally bound,
makunboundaffects the most local existing binding. This is the only way a symbol can have a void local binding, since all the constructs that create local bindings create them with values. In this case, the voidness lasts at most as long as the binding does; when the binding is removed due to exit from the construct that made it, the previous local or global binding is reexposed as usual, and the variable is no longer void unless the newly reexposed binding was void all along.(setq x 1) ; Put a value in the global binding. => 1 (let ((x 2)) ; Locally bind it. (makunbound 'x) ; Void the local binding. x) error--> Symbol's value as variable is void: x x ; The global binding is unchanged. => 1 (let ((x 2)) ; Locally bind it. (let ((x 3)) ; And again. (makunbound 'x) ; Void the innermost-local binding. x)) ; And refer: it's void. error--> Symbol's value as variable is void: x (let ((x 2)) (let ((x 3)) (makunbound 'x)) ; Void inner binding, then remove it. x) ; Now outerletbinding is visible. => 2
A variable that has been made void with makunbound is
indistinguishable from one that has never received a value and has
always been void.
You can use the function boundp to test whether a variable is
currently void.
boundpreturnstif variable (a symbol) is not void; more precisely, if its current binding is not void. It returnsnilotherwise.(boundp 'abracadabra) ; Starts out void. => nil (let ((abracadabra 5)) ; Locally bind it. (boundp 'abracadabra)) => t (boundp 'abracadabra) ; Still globally void. => nil (setq abracadabra 5) ; Make it globally nonvoid. => 5 (boundp 'abracadabra) => t
You may announce your intention to use a symbol as a global variable
with a variable definition: a special form, either defconst
or defvar.
In Emacs Lisp, definitions serve three purposes. First, they inform
people who read the code that certain symbols are intended to be
used a certain way (as variables). Second, they inform the Lisp system
of these things, supplying a value and documentation. Third, they
provide information to utilities such as etags and
make-docfile, which create data bases of the functions and
variables in a program.
The difference between defconst and defvar is primarily
a matter of intent, serving to inform human readers of whether the value
should ever change. Emacs Lisp does not restrict the ways in which a
variable can be used based on defconst or defvar
declarations. However, it does make a difference for initialization:
defconst unconditionally initializes the variable, while
defvar initializes it only if it is void.
This special form defines symbol as a variable and can also initialize and document it. The definition informs a person reading your code that symbol is used as a variable that might be set or changed. Note that symbol is not evaluated; the symbol to be defined must appear explicitly in the
defvar.If symbol is void and value is specified,
defvarevaluates it and sets symbol to the result. But if symbol already has a value (i.e., it is not void), value is not even evaluated, and symbol's value remains unchanged. If value is omitted, the value of symbol is not changed in any case.If symbol has a buffer-local binding in the current buffer,
defvaroperates on the default value, which is buffer-independent, not the current (buffer-local) binding. It sets the default value if the default value is void. See Buffer-Local Variables.When you evaluate a top-level
defvarform with C-M-x in Emacs Lisp mode (eval-defun), a special feature ofeval-defunarranges to set the variable unconditionally, without testing whether its value is void.If the doc-string argument appears, it specifies the documentation for the variable. (This opportunity to specify documentation is one of the main benefits of defining the variable.) The documentation is stored in the symbol's
variable-documentationproperty. The Emacs help functions (see Documentation) look for this property.If the variable is a user option that users would want to set interactively, you should use ‘*’ as the first character of doc-string. This lets users set the variable conveniently using the
set-variablecommand. Note that you should nearly always usedefcustominstead ofdefvarto define these variables, so that users can use M-x customize and related commands to set them. See Customization.Here are some examples. This form defines
foobut does not initialize it:(defvar foo) => fooThis example initializes the value of
barto23, and gives it a documentation string:(defvar bar 23 "The normal weight of a bar.") => barThe following form changes the documentation string for
bar, making it a user option, but does not change the value, sincebaralready has a value. (The addition(1+ nil)would get an error if it were evaluated, but since it is not evaluated, there is no error.)(defvar bar (1+ nil) "*The normal weight of a bar.") => bar bar => 23Here is an equivalent expression for the
defvarspecial form:(defvar symbol value doc-string) == (progn (if (not (boundp 'symbol)) (setq symbol value)) (if 'doc-string (put 'symbol 'variable-documentation 'doc-string)) 'symbol)The
defvarform returns symbol, but it is normally used at top level in a file where its value does not matter.
This special form defines symbol as a value and initializes it. It informs a person reading your code that symbol has a standard global value, established here, that should not be changed by the user or by other programs. Note that symbol is not evaluated; the symbol to be defined must appear explicitly in the
defconst.
defconstalways evaluates value, and sets the value of symbol to the result if value is given. If symbol does have a buffer-local binding in the current buffer,defconstsets the default value, not the buffer-local value. (But you should not be making buffer-local bindings for a symbol that is defined withdefconst.)Here,
piis a constant that presumably ought not to be changed by anyone (attempts by the Indiana State Legislature notwithstanding). As the second form illustrates, however, this is only advisory.(defconst pi 3.1415 "Pi to five places.") => pi (setq pi 3) => pi pi => 3
This function returns
tif variable is a user option—a variable intended to be set by the user for customization—andnilotherwise. (Variables other than user options exist for the internal purposes of Lisp programs, and users need not know about them.)User option variables are distinguished from other variables either though being declared using
defcustom4 or by the first character of theirvariable-documentationproperty. If the property exists and is a string, and its first character is ‘*’, then the variable is a user option.
If a user option variable has a variable-interactive property,
the set-variable command uses that value to control reading the
new value for the variable. The property's value is used as if it were
specified in interactive (see Using Interactive). However,
this feature is largely obsoleted by defcustom
(see Customization).
Warning: If the defconst and defvar special
forms are used while the variable has a local binding, they set the
local binding's value; the global binding is not changed. This is not
what you usually want. To prevent it, use these special forms at top
level in a file, where normally no local binding is in effect, and make
sure to load the file before making a local binding for the variable.
When you define a variable whose value is a function, or a list of functions, use a name that ends in ‘-function’ or ‘-functions’, respectively.
There are several other variable name conventions; here is a complete list:
nil for “good” arguments and nil for “bad”
arguments.
nil or not.
When you define a variable, always consider whether you should mark it as “risky”; see File Local Variables.
When defining and initializing a variable that holds a complicated
value (such as a keymap with bindings in it), it's best to put the
entire computation of the value into the defvar, like this:
(defvar my-mode-map
(let ((map (make-sparse-keymap)))
(define-key map "\C-c\C-a" 'my-command)
...
map)
docstring)
This method has several benefits. First, if the user quits while
loading the file, the variable is either still uninitialized or
initialized properly, never in-between. If it is still uninitialized,
reloading the file will initialize it properly. Second, reloading the
file once the variable is initialized will not alter it; that is
important if the user has run hooks to alter part of the contents (such
as, to rebind keys). Third, evaluating the defvar form with
C-M-x will reinitialize the map completely.
Putting so much code in the defvar form has one disadvantage:
it puts the documentation string far away from the line which names the
variable. Here's a safe way to avoid that:
(defvar my-mode-map nil
docstring)
(unless my-mode-map
(let ((map (make-sparse-keymap)))
(define-key map "\C-c\C-a" 'my-command)
...
(setq my-mode-map map)))
This has all the same advantages as putting the initialization inside
the defvar, except that you must type C-M-x twice, once on
each form, if you do want to reinitialize the variable.
But be careful not to write the code like this:
(defvar my-mode-map nil
docstring)
(unless my-mode-map
(setq my-mode-map (make-sparse-keymap))
(define-key my-mode-map "\C-c\C-a" 'my-command)
...)
This code sets the variable, then alters it, but it does so in more than
one step. If the user quits just after the setq, that leaves the
variable neither correctly initialized nor void nor nil. Once
that happens, reloading the file will not initialize the variable; it
will remain incomplete.
The usual way to reference a variable is to write the symbol which
names it (see Symbol Forms). This requires you to specify the
variable name when you write the program. Usually that is exactly what
you want to do. Occasionally you need to choose at run time which
variable to reference; then you can use symbol-value.
This function returns the value of symbol. This is the value in the innermost local binding of the symbol, or its global value if it has no local bindings.
(setq abracadabra 5) => 5 (setq foo 9) => 9 ;; Here the symbolabracadabra;; is the symbol whose value is examined. (let ((abracadabra 'foo)) (symbol-value 'abracadabra)) => foo ;; Here the value ofabracadabra, ;; which isfoo, ;; is the symbol whose value is examined. (let ((abracadabra 'foo)) (symbol-value abracadabra)) => 9 (symbol-value 'abracadabra) => 5A
void-variableerror is signaled if the current binding of symbol is void.
The usual way to change the value of a variable is with the special
form setq. When you need to compute the choice of variable at
run time, use the function set.
This special form is the most common method of changing a variable's value. Each symbol is given a new value, which is the result of evaluating the corresponding form. The most-local existing binding of the symbol is changed.
setqdoes not evaluate symbol; it sets the symbol that you write. We say that this argument is automatically quoted. The ‘q’ insetqstands for “quoted.”The value of the
setqform is the value of the last form.(setq x (1+ 2)) => 3 x ;xnow has a global value. => 3 (let ((x 5)) (setq x 6) ; The local binding ofxis set. x) => 6 x ; The global value is unchanged. => 3Note that the first form is evaluated, then the first symbol is set, then the second form is evaluated, then the second symbol is set, and so on:
(setq x 10 ; Notice thatxis set before y (1+ x)) ; the value ofyis computed. => 11
This function sets symbol's value to value, then returns value. Since
setis a function, the expression written for symbol is evaluated to obtain the symbol to set.The most-local existing binding of the variable is the binding that is set; shadowed bindings are not affected.
(set one 1) error--> Symbol's value as variable is void: one (set 'one 1) => 1 (set 'two 'one) => one (set two 2) ;twoevaluates to symbolone. => 2 one ; So it isonethat was set. => 2 (let ((one 1)) ; This binding ofoneis set, (set 'one 3) ; not the global value. one) => 3 one => 2If symbol is not actually a symbol, a
wrong-type-argumenterror is signaled.(set '(x y) 'z) error--> Wrong type argument: symbolp, (x y)Logically speaking,
setis a more fundamental primitive thansetq. Any use ofsetqcan be trivially rewritten to useset;setqcould even be defined as a macro, given the availability ofset. However,setitself is rarely used; beginners hardly need to know about it. It is useful only for choosing at run time which variable to set. For example, the commandset-variable, which reads a variable name from the user and then sets the variable, needs to useset.Common Lisp note: In Common Lisp,setalways changes the symbol's “special” or dynamic value, ignoring any lexical bindings. In Emacs Lisp, all variables and all bindings are dynamic, sosetalways affects the most local existing binding.
One other function for setting a variable is designed to add an element to a list if it is not already present in the list.
This function sets the variable symbol by consing element onto the old value, if element is not already a member of that value. It returns the resulting list, whether updated or not. The value of symbol had better be a list already before the call.
The argument symbol is not implicitly quoted;
add-to-listis an ordinary function, likesetand unlikesetq. Quote the argument yourself if that is what you want.
Here's a scenario showing how to use add-to-list:
(setq foo '(a b))
=> (a b)
(add-to-list 'foo 'c) ;; Add c.
=> (c a b)
(add-to-list 'foo 'b) ;; No effect.
=> (c a b)
foo ;; foo was changed.
=> (c a b)
An equivalent expression for (add-to-list 'var
value) is this:
(or (member value var)
(setq var (cons value var)))
A given symbol foo can have several local variable bindings,
established at different places in the Lisp program, as well as a global
binding. The most recently established binding takes precedence over
the others.
Local bindings in Emacs Lisp have indefinite scope and dynamic extent. Scope refers to where textually in the source code the binding can be accessed. “Indefinite scope” means that any part of the program can potentially access the variable binding. Extent refers to when, as the program is executing, the binding exists. “Dynamic extent” means that the binding lasts as long as the activation of the construct that established it.
The combination of dynamic extent and indefinite scope is called dynamic scoping. By contrast, most programming languages use lexical scoping, in which references to a local variable must be located textually within the function or block that binds the variable.
Common Lisp note: Variables declared “special” in Common Lisp are dynamically scoped, like all variables in Emacs Lisp.
Emacs Lisp uses indefinite scope for local variable bindings. This means that any function anywhere in the program text might access a given binding of a variable. Consider the following function definitions:
(defun binder (x) ;xis bound inbinder. (foo 5)) ;foois some other function. (defun user () ;xis used ``free'' inuser. (list x))
In a lexically scoped language, the binding of x in
binder would never be accessible in user, because
user is not textually contained within the function
binder. However, in dynamically-scoped Emacs Lisp, user
may or may not refer to the binding of x established in
binder, depending on the circumstances:
user directly without calling binder at all,
then whatever binding of x is found, it cannot come from
binder.
foo as follows and then call binder, then the
binding made in binder will be seen in user:
(defun foo (lose)
(user))
foo as follows and then call binder,
then the binding made in binder will not be seen in
user:
(defun foo (x)
(user))
Here, when foo is called by binder, it binds x.
(The binding in foo is said to shadow the one made in
binder.) Therefore, user will access the x bound
by foo instead of the one bound by binder.
Emacs Lisp uses dynamic scoping because simple implementations of lexical scoping are slow. In addition, every Lisp system needs to offer dynamic scoping at least as an option; if lexical scoping is the norm, there must be a way to specify dynamic scoping instead for a particular variable. It might not be a bad thing for Emacs to offer both, but implementing it with dynamic scoping only was much easier.
Extent refers to the time during program execution that a variable name is valid. In Emacs Lisp, a variable is valid only while the form that bound it is executing. This is called dynamic extent. “Local” or “automatic” variables in most languages, including C and Pascal, have dynamic extent.
One alternative to dynamic extent is indefinite extent. This means that a variable binding can live on past the exit from the form that made the binding. Common Lisp and Scheme, for example, support this, but Emacs Lisp does not.
To illustrate this, the function below, make-add, returns a
function that purports to add n to its own argument m. This
would work in Common Lisp, but it does not do the job in Emacs Lisp,
because after the call to make-add exits, the variable n
is no longer bound to the actual argument 2.
(defun make-add (n)
(function (lambda (m) (+ n m)))) ; Return a function.
=> make-add
(fset 'add2 (make-add 2)) ; Define function add2
; with (make-add 2).
=> (lambda (m) (+ n m))
(add2 4) ; Try to add 2 to 4.
error--> Symbol's value as variable is void: n
Some Lisp dialects have “closures”, objects that are like functions but record additional variable bindings. Emacs Lisp does not have closures.
A simple sample implementation (which is not how Emacs Lisp actually works) may help you understand dynamic binding. This technique is called deep binding and was used in early Lisp systems.
Suppose there is a stack of bindings, which are variable-value pairs.
At entry to a function or to a let form, we can push bindings
onto the stack for the arguments or local variables created there. We
can pop those bindings from the stack at exit from the binding
construct.
We can find the value of a variable by searching the stack from top to bottom for a binding for that variable; the value from that binding is the value of the variable. To set the variable, we search for the current binding, then store the new value into that binding.
As you can see, a function's bindings remain in effect as long as it continues execution, even during its calls to other functions. That is why we say the extent of the binding is dynamic. And any other function can refer to the bindings, if it uses the same variables while the bindings are in effect. That is why we say the scope is indefinite.
The actual implementation of variable scoping in GNU Emacs Lisp uses a technique called shallow binding. Each variable has a standard place in which its current value is always found—the value cell of the symbol.
In shallow binding, setting the variable works by storing a value in the value cell. Creating a new binding works by pushing the old value (belonging to a previous binding) onto a stack, and storing the new local value in the value cell. Eliminating a binding works by popping the old value off the stack, into the value cell.
We use shallow binding because it has the same results as deep binding, but runs faster, since there is never a need to search for a binding.
Binding a variable in one function and using it in another is a powerful technique, but if used without restraint, it can make programs hard to understand. There are two clean ways to use this technique:
You should write comments to inform other programmers that they can see all uses of the variable before them, and to advise them not to add uses elsewhere.
case-fold-search is defined as “non-nil means ignore case
when searching”; various search and replace functions refer to it
directly or through their subroutines, but do not bind or set it.
Then you can bind the variable in other programs, knowing reliably what the effect will be.
In either case, you should define the variable with defvar.
This helps other people understand your program by telling them to look
for inter-function usage. It also avoids a warning from the byte
compiler. Choose the variable's name to avoid name conflicts—don't
use short names like x.
Global and local variable bindings are found in most programming languages in one form or another. Emacs, however, also supports additional, unusual kinds of variable binding: buffer-local bindings, which apply only in one buffer, and frame-local bindings, which apply only in one frame. Having different values for a variable in different buffers and/or frames is an important customization method.
This section describes buffer-local bindings; for frame-local bindings, see the following section, Frame-Local Variables. (A few variables have bindings that are local to each terminal; see Multiple Displays.)
A buffer-local variable has a buffer-local binding associated with a particular buffer. The binding is in effect when that buffer is current; otherwise, it is not in effect. If you set the variable while a buffer-local binding is in effect, the new value goes in that binding, so its other bindings are unchanged. This means that the change is visible only in the buffer where you made it.
The variable's ordinary binding, which is not associated with any specific buffer, is called the default binding. In most cases, this is the global binding.
A variable can have buffer-local bindings in some buffers but not in other buffers. The default binding is shared by all the buffers that don't have their own bindings for the variable. (This includes all newly-created buffers.) If you set the variable in a buffer that does not have a buffer-local binding for it, this sets the default binding (assuming there are no frame-local bindings to complicate the matter), so the new value is visible in all the buffers that see the default binding.
The most common use of buffer-local bindings is for major modes to change
variables that control the behavior of commands. For example, C mode and
Lisp mode both set the variable paragraph-start to specify that only
blank lines separate paragraphs. They do this by making the variable
buffer-local in the buffer that is being put into C mode or Lisp mode, and
then setting it to the new value for that mode. See Major Modes.
The usual way to make a buffer-local binding is with
make-local-variable, which is what major mode commands typically
use. This affects just the current buffer; all other buffers (including
those yet to be created) will continue to share the default value unless
they are explicitly given their own buffer-local bindings.
A more powerful operation is to mark the variable as
automatically buffer-local by calling
make-variable-buffer-local. You can think of this as making the
variable local in all buffers, even those yet to be created. More
precisely, the effect is that setting the variable automatically makes
the variable local to the current buffer if it is not already so. All
buffers start out by sharing the default value of the variable as usual,
but setting the variable creates a buffer-local binding for the current
buffer. The new value is stored in the buffer-local binding, leaving
the default binding untouched. This means that the default value cannot
be changed with setq in any buffer; the only way to change it is
with setq-default.
Warning: When a variable has buffer-local values in one or
more buffers, you can get Emacs very confused by binding the variable
with let, changing to a different current buffer in which a
different binding is in effect, and then exiting the let. This
can scramble the values of the buffer-local and default bindings.
To preserve your sanity, avoid using a variable in that way. If you
use save-excursion around each piece of code that changes to a
different current buffer, you will not have this problem
(see Excursions). Here is an example of what to avoid:
(setq foo 'b)
(set-buffer "a")
(make-local-variable 'foo)
(setq foo 'a)
(let ((foo 'temp))
(set-buffer "b")
body...)
foo => 'a ; The old buffer-local value from buffer ‘a’
; is now the default value.
(set-buffer "a")
foo => 'temp ; The local let value that should be gone
; is now the buffer-local value in buffer ‘a’.
But save-excursion as shown here avoids the problem:
(let ((foo 'temp))
(save-excursion
(set-buffer "b")
body...))
Note that references to foo in body access the
buffer-local binding of buffer ‘b’.
When a file specifies local variable values, these become buffer-local values when you visit the file. See File Variables.
This function creates a buffer-local binding in the current buffer for variable (a symbol). Other buffers are not affected. The value returned is variable.
The buffer-local value of variable starts out as the same value variable previously had. If variable was void, it remains void.
;; In buffer ‘b1’: (setq foo 5) ; Affects all buffers. => 5 (make-local-variable 'foo) ; Now it is local in ‘b1’. => foo foo ; That did not change => 5 ; the value. (setq foo 6) ; Change the value => 6 ; in ‘b1’. foo => 6 ;; In buffer ‘b2’, the value hasn't changed. (save-excursion (set-buffer "b2") foo) => 5Making a variable buffer-local within a
let-binding for that variable does not work reliably, unless the buffer in which you do this is not current either on entry to or exit from thelet. This is becauseletdoes not distinguish between different kinds of bindings; it knows only which variable the binding was made for.If the variable is terminal-local, this function signals an error. Such variables cannot have buffer-local bindings as well. See Multiple Displays.
Note: Do not use
make-local-variablefor a hook variable. Instead, usemake-local-hook. See Hooks.
This function marks variable (a symbol) automatically buffer-local, so that any subsequent attempt to set it will make it local to the current buffer at the time.
A peculiar wrinkle of this feature is that binding the variable (with
letor other binding constructs) does not create a buffer-local binding for it. Only setting the variable (withsetorsetq) does so.The value returned is variable.
Warning: Don't assume that you should use
make-variable-buffer-localfor user-option variables, simply because users might want to customize them differently in different buffers. Users can make any variable local, when they wish to. It is better to leave the choice to them.The time to use
make-variable-buffer-localis when it is crucial that no two buffers ever share the same binding. For example, when a variable is used for internal purposes in a Lisp program which depends on having separate values in separate buffers, then usingmake-variable-buffer-localcan be the best solution.
This returns
tif variable is buffer-local in buffer buffer (which defaults to the current buffer); otherwise,nil.
This function returns a list describing the buffer-local variables in buffer buffer. (If buffer is omitted, the current buffer is used.) It returns an association list (see Association Lists) in which each element contains one buffer-local variable and its value. However, when a variable's buffer-local binding in buffer is void, then the variable appears directly in the resulting list.
(make-local-variable 'foobar) (makunbound 'foobar) (make-local-variable 'bind-me) (setq bind-me 69) (setq lcl (buffer-local-variables)) ;; First, built-in variables local in all buffers: => ((mark-active . nil) (buffer-undo-list . nil) (mode-name . "Fundamental") ... ;; Next, non-built-in buffer-local variables. ;; This one is buffer-local and void: foobar ;; This one is buffer-local and nonvoid: (bind-me . 69))Note that storing new values into the cdrs of cons cells in this list does not change the buffer-local values of the variables.
This function deletes the buffer-local binding (if any) for variable (a symbol) in the current buffer. As a result, the default binding of variable becomes visible in this buffer. This typically results in a change in the value of variable, since the default value is usually different from the buffer-local value just eliminated.
If you kill the buffer-local binding of a variable that automatically becomes buffer-local when set, this makes the default value visible in the current buffer. However, if you set the variable again, that will once again create a buffer-local binding for it.
kill-local-variablereturns variable.This function is a command because it is sometimes useful to kill one buffer-local variable interactively, just as it is useful to create buffer-local variables interactively.
This function eliminates all the buffer-local variable bindings of the current buffer except for variables marked as “permanent”. As a result, the buffer will see the default values of most variables.
This function also resets certain other information pertaining to the buffer: it sets the local keymap to
nil, the syntax table to the value of(standard-syntax-table), the case table to(standard-case-table), and the abbrev table to the value offundamental-mode-abbrev-table.The very first thing this function does is run the normal hook
change-major-mode-hook(see below).Every major mode command begins by calling this function, which has the effect of switching to Fundamental mode and erasing most of the effects of the previous major mode. To ensure that this does its job, the variables that major modes set should not be marked permanent.
kill-all-local-variablesreturnsnil.
The function
kill-all-local-variablesruns this normal hook before it does anything else. This gives major modes a way to arrange for something special to be done if the user switches to a different major mode. For best results, make this variable buffer-local, so that it will disappear after doing its job and will not interfere with the subsequent major mode. See Hooks.
A buffer-local variable is permanent if the variable name (a
symbol) has a permanent-local property that is non-nil.
Permanent locals are appropriate for data pertaining to where the file
came from or how to save it, rather than with how to edit the contents.
The global value of a variable with buffer-local bindings is also called the default value, because it is the value that is in effect whenever neither the current buffer nor the selected frame has its own binding for the variable.
The functions default-value and setq-default access and
change a variable's default value regardless of whether the current
buffer has a buffer-local binding. For example, you could use
setq-default to change the default setting of
paragraph-start for most buffers; and this would work even when
you are in a C or Lisp mode buffer that has a buffer-local value for
this variable.
The special forms defvar and defconst also set the
default value (if they set the variable at all), rather than any
buffer-local or frame-local value.
This function returns symbol's default value. This is the value that is seen in buffers and frames that do not have their own values for this variable. If symbol is not buffer-local, this is equivalent to
symbol-value(see Accessing Variables).
The function
default-boundptells you whether symbol's default value is nonvoid. If(default-boundp 'foo)returnsnil, then(default-value 'foo)would get an error.
default-boundpis todefault-valueasboundpis tosymbol-value.
This special form gives each symbol a new default value, which is the result of evaluating the corresponding form. It does not evaluate symbol, but does evaluate form. The value of the
setq-defaultform is the value of the last form.If a symbol is not buffer-local for the current buffer, and is not marked automatically buffer-local,
setq-defaulthas the same effect assetq. If symbol is buffer-local for the current buffer, then this changes the value that other buffers will see (as long as they don't have a buffer-local value), but not the value that the current buffer sees.;; In buffer ‘foo’: (make-local-variable 'buffer-local) => buffer-local (setq buffer-local 'value-in-foo) => value-in-foo (setq-default buffer-local 'new-default) => new-default buffer-local => value-in-foo (default-value 'buffer-local) => new-default ;; In (the new) buffer ‘bar’: buffer-local => new-default (default-value 'buffer-local) => new-default (setq buffer-local 'another-default) => another-default (default-value 'buffer-local) => another-default ;; Back in buffer ‘foo’: buffer-local => value-in-foo (default-value 'buffer-local) => another-default
This function is like
setq-default, except that symbol is an ordinary evaluated argument.(set-default (car '(a b c)) 23) => 23 (default-value 'a) => 23
Just as variables can have buffer-local bindings, they can also have
frame-local bindings. These bindings belong to one frame, and are in
effect when that frame is selected. Frame-local bindings are actually
frame parameters: you create a frame-local binding in a specific frame
by calling modify-frame-parameters and specifying the variable
name as the parameter name.
To enable frame-local bindings for a certain variable, call the function
make-variable-frame-local.
Enable the use of frame-local bindings for variable. This does not in itself create any frame-local bindings for the variable; however, if some frame already has a value for variable as a frame parameter, that value automatically becomes a frame-local binding.
If the variable is terminal-local, this function signals an error, because such variables cannot have frame-local bindings as well. See Multiple Displays. A few variables that are implemented specially in Emacs can be (and usually are) buffer-local, but can never be frame-local.
Buffer-local bindings take precedence over frame-local bindings. Thus,
consider a variable foo: if the current buffer has a buffer-local
binding for foo, that binding is active; otherwise, if the
selected frame has a frame-local binding for foo, that binding is
active; otherwise, the default binding of foo is active.
Here is an example. First we prepare a few bindings for foo:
(setq f1 (selected-frame))
(make-variable-frame-local 'foo)
;; Make a buffer-local binding for foo in ‘b1’.
(set-buffer (get-buffer-create "b1"))
(make-local-variable 'foo)
(setq foo '(b 1))
;; Make a frame-local binding for foo in a new frame.
;; Store that frame in f2.
(setq f2 (make-frame))
(modify-frame-parameters f2 '((foo . (f 2))))
Now we examine foo in various contexts. Whenever the
buffer ‘b1’ is current, its buffer-local binding is in effect,
regardless of the selected frame:
(select-frame f1)
(set-buffer (get-buffer-create "b1"))
foo
=> (b 1)
(select-frame f2)
(set-buffer (get-buffer-create "b1"))
foo
=> (b 1)
Otherwise, the frame gets a chance to provide the binding; when frame
f2 is selected, its frame-local binding is in effect:
(select-frame f2)
(set-buffer (get-buffer "*scratch*"))
foo
=> (f 2)
When neither the current buffer nor the selected frame provides a binding, the default binding is used:
(select-frame f1)
(set-buffer (get-buffer "*scratch*"))
foo
=> nil
When the active binding of a variable is a frame-local binding, setting
the variable changes that binding. You can observe the result with
frame-parameters:
(select-frame f2)
(set-buffer (get-buffer "*scratch*"))
(setq foo 'nobody)
(assq 'foo (frame-parameters f2))
=> (foo . nobody)
We have considered the idea of bindings that are local to a category
of frames—for example, all color frames, or all frames with dark
backgrounds. We have not implemented them because it is not clear that
this feature is really useful. You can get more or less the same
results by adding a function to after-make-frame-functions, set up to
define a particular frame parameter according to the appropriate
conditions for each frame.
It would also be possible to implement window-local bindings. We don't know of many situations where they would be useful, and it seems that indirect buffers (see Indirect Buffers) with buffer-local bindings offer a way to handle these situations more robustly.
If sufficient application is found for either of these two kinds of local bindings, we will provide it in a subsequent Emacs version.
This section describes the functions and variables that affect processing of local variables lists in files.
This variable controls whether to process file local variables lists. A value of
tmeans process the local variables lists unconditionally;nilmeans ignore them; anything else means ask the user what to do for each file. The default value ist.
This function parses, and binds or evaluates as appropriate, any local variables specified by the contents of the current buffer. The variable
enable-local-variableshas its effect here.The argument force usually comes from the argument find-file given to
normal-mode.
If a file local variable list could specify the a function that will be called later, or an expression that will be executed later, simply visiting a file could take over your Emacs. To prevent this, Emacs takes care not to allow local variable lists to set such variables.
For one thing, any variable whose name ends in ‘-function’, ‘-functions’, ‘-hook’, ‘-hooks’, ‘-form’, ‘-forms’, ‘-program’, ‘-command’ or ‘-predicate’ cannot be set in a local variable list. In general, you should use such a name whenever it is appropriate for the variable's meaning.
In addition, any variable whose name has a non-nil
risky-local-variable property is also ignored. So are
all variables listed in ignored-local-variables:
This variable holds a list of variables that should not be set by a file's local variables list. Any value specified for one of these variables is ignored.
The ‘Eval:’ “variable” is also a potential loophole, so Emacs normally asks for confirmation before handling it.
This variable controls processing of ‘Eval:’ in local variables lists in files being visited. A value of
tmeans process them unconditionally;nilmeans ignore them; anything else means ask the user what to do for each file. The default value ismaybe.
A Lisp program is composed mainly of Lisp functions. This chapter explains what functions are, how they accept arguments, and how to define them.
In a general sense, a function is a rule for carrying on a computation given several values called arguments. The result of the computation is called the value of the function. The computation can also have side effects: lasting changes in the values of variables or the contents of data structures.
Here are important terms for functions in Emacs Lisp and for other function-like objects.
car or append. These functions are also called
built-in functions or subrs. (Special forms are also
considered primitives.)
Usually the reason we implement a function as a primitive is either
because it is fundamental, because it provides a low-level interface to
operating system services, or because it needs to run fast. Primitives
can be modified or added only by changing the C sources and recompiling
the editor. See Writing Emacs Primitives.
command-execute can invoke; it
is a possible definition for a key sequence. Some functions are
commands; a function written in Lisp is a command if it contains an
interactive declaration (see Defining Commands). Such a function
can be called from Lisp expressions like other functions; in this case,
the fact that the function is a command makes no difference.
Keyboard macros (strings and vectors) are commands also, even though
they are not functions. A symbol is a command if its function
definition is a command; such symbols can be invoked with M-x.
The symbol is a function as well if the definition is a function.
See Command Overview.
This function returns
tif object is any kind of function, or a special form or macro.
This function returns
tif object is a built-in function (i.e., a Lisp primitive).(subrp 'message) ;messageis a symbol, => nil ; not a subr object. (subrp (symbol-function 'message)) => t
This function returns
tif object is a byte-code function. For example:(byte-code-function-p (symbol-function 'next-line)) => t
This function provides information about the argument list of a primitive, subr. The returned value is a pair
(min.max). min is the minimum number of args. max is the maximum number or the symbolmany, for a function with&restarguments, or the symbolunevalledif subr is a special form.
A function written in Lisp is a list that looks like this:
(lambda (arg-variables...)
[documentation-string]
[interactive-declaration]
body-forms...)
Such a list is called a lambda expression. In Emacs Lisp, it actually is valid as an expression—it evaluates to itself. In some other Lisp dialects, a lambda expression is not a valid expression at all. In either case, its main use is not to be evaluated as an expression, but to be called as a function.
A function written in Lisp (a “lambda expression”) is a list that looks like this:
(lambda (arg-variables...)
[documentation-string]
[interactive-declaration]
body-forms...)
The first element of a lambda expression is always the symbol
lambda. This indicates that the list represents a function. The
reason functions are defined to start with lambda is so that
other lists, intended for other uses, will not accidentally be valid as
functions.
The second element is a list of symbols—the argument variable names. This is called the lambda list. When a Lisp function is called, the argument values are matched up against the variables in the lambda list, which are given local bindings with the values provided. See Local Variables.
The documentation string is a Lisp string object placed within the function definition to describe the function for the Emacs help facilities. See Function Documentation.
The interactive declaration is a list of the form (interactive
code-string). This declares how to provide arguments if the
function is used interactively. Functions with this declaration are called
commands; they can be called using M-x or bound to a key.
Functions not intended to be called in this way should not have interactive
declarations. See Defining Commands, for how to write an interactive
declaration.
The rest of the elements are the body of the function: the Lisp code to do the work of the function (or, as a Lisp programmer would say, “a list of Lisp forms to evaluate”). The value returned by the function is the value returned by the last element of the body.
Consider for example the following function:
(lambda (a b c) (+ a b c))
We can call this function by writing it as the car of an expression, like this:
((lambda (a b c) (+ a b c))
1 2 3)
This call evaluates the body of the lambda expression with the variable
a bound to 1, b bound to 2, and c bound to 3.
Evaluation of the body adds these three numbers, producing the result 6;
therefore, this call to the function returns the value 6.
Note that the arguments can be the results of other function calls, as in this example:
((lambda (a b c) (+ a b c))
1 (* 2 3) (- 5 4))
This evaluates the arguments 1, (* 2 3), and (- 5
4) from left to right. Then it applies the lambda expression to the
argument values 1, 6 and 1 to produce the value 8.
It is not often useful to write a lambda expression as the car of
a form in this way. You can get the same result, of making local
variables and giving them values, using the special form let
(see Local Variables). And let is clearer and easier to use.
In practice, lambda expressions are either stored as the function
definitions of symbols, to produce named functions, or passed as
arguments to other functions (see Anonymous Functions).
However, calls to explicit lambda expressions were very useful in the
old days of Lisp, before the special form let was invented. At
that time, they were the only way to bind and initialize local
variables.
Our simple sample function, (lambda (a b c) (+ a b c)),
specifies three argument variables, so it must be called with three
arguments: if you try to call it with only two arguments or four
arguments, you get a wrong-number-of-arguments error.
It is often convenient to write a function that allows certain
arguments to be omitted. For example, the function substring
accepts three arguments—a string, the start index and the end
index—but the third argument defaults to the length of the
string if you omit it. It is also convenient for certain functions to
accept an indefinite number of arguments, as the functions list
and + do.
To specify optional arguments that may be omitted when a function
is called, simply include the keyword &optional before the optional
arguments. To specify a list of zero or more extra arguments, include the
keyword &rest before one final argument.
Thus, the complete syntax for an argument list is as follows:
(required-vars...
[&optional optional-vars...]
[&rest rest-var])
The square brackets indicate that the &optional and &rest
clauses, and the variables that follow them, are optional.
A call to the function requires one actual argument for each of the
required-vars. There may be actual arguments for zero or more of
the optional-vars, and there cannot be any actual arguments beyond
that unless the lambda list uses &rest. In that case, there may
be any number of extra actual arguments.
If actual arguments for the optional and rest variables are omitted,
then they always default to nil. There is no way for the
function to distinguish between an explicit argument of nil and
an omitted argument. However, the body of the function is free to
consider nil an abbreviation for some other meaningful value.
This is what substring does; nil as the third argument to
substring means to use the length of the string supplied.
Common Lisp note: Common Lisp allows the function to specify what
default value to use when an optional argument is omitted; Emacs Lisp
always uses nil. Emacs Lisp does not support “supplied-p”
variables that tell you whether an argument was explicitly passed.
For example, an argument list that looks like this:
(a b &optional c d &rest e)
binds a and b to the first two actual arguments, which are
required. If one or two more arguments are provided, c and
d are bound to them respectively; any arguments after the first
four are collected into a list and e is bound to that list. If
there are only two arguments, c is nil; if two or three
arguments, d is nil; if four arguments or fewer, e
is nil.
There is no way to have required arguments following optional
ones—it would not make sense. To see why this must be so, suppose
that c in the example were optional and d were required.
Suppose three actual arguments are given; which variable would the
third argument be for? Would it be used for the c, or for
d? One can argue for both possibilities. Similarly, it makes
no sense to have any more arguments (either required or optional)
after a &rest argument.
Here are some examples of argument lists and proper calls:
((lambda (n) (1+ n)) ; One required: 1) ; requires exactly one argument. => 2 ((lambda (n &optional n1) ; One required and one optional: (if n1 (+ n n1) (1+ n))) ; 1 or 2 arguments. 1 2) => 3 ((lambda (n &rest ns) ; One required and one rest: (+ n (apply '+ ns))) ; 1 or more arguments. 1 2 3 4 5) => 15
A lambda expression may optionally have a documentation string just after the lambda list. This string does not affect execution of the function; it is a kind of comment, but a systematized comment which actually appears inside the Lisp world and can be used by the Emacs help facilities. See Documentation, for how the documentation-string is accessed.
It is a good idea to provide documentation strings for all the functions in your program, even those that are called only from within your program. Documentation strings are like comments, except that they are easier to access.
The first line of the documentation string should stand on its own,
because apropos displays just this first line. It should consist
of one or two complete sentences that summarize the function's purpose.
The start of the documentation string is usually indented in the source file, but since these spaces come before the starting double-quote, they are not part of the string. Some people make a practice of indenting any additional lines of the string so that the text lines up in the program source. This is a mistake. The indentation of the following lines is inside the string; what looks nice in the source code will look ugly when displayed by the help commands.
You may wonder how the documentation string could be optional, since there are required components of the function that follow it (the body). Since evaluation of a string returns that string, without any side effects, it has no effect if it is not the last form in the body. Thus, in practice, there is no confusion between the first form of the body and the documentation string; if the only body form is a string then it serves both as the return value and as the documentation.
In most computer languages, every function has a name; the idea of a
function without a name is nonsensical. In Lisp, a function in the
strictest sense has no name. It is simply a list whose first element is
lambda, a byte-code function object, or a primitive subr-object.
However, a symbol can serve as the name of a function. This happens when you put the function in the symbol's function cell (see Symbol Components). Then the symbol itself becomes a valid, callable function, equivalent to the list or subr-object that its function cell refers to. The contents of the function cell are also called the symbol's function definition. The procedure of using a symbol's function definition in place of the symbol is called symbol function indirection; see Function Indirection.
In practice, nearly all functions are given names in this way and
referred to through their names. For example, the symbol car works
as a function and does what it does because the primitive subr-object
#<subr car> is stored in its function cell.
We give functions names because it is convenient to refer to them by
their names in Lisp expressions. For primitive subr-objects such as
#<subr car>, names are the only way you can refer to them: there
is no read syntax for such objects. For functions written in Lisp, the
name is more convenient to use in a call than an explicit lambda
expression. Also, a function with a name can refer to itself—it can
be recursive. Writing the function's name in its own definition is much
more convenient than making the function definition point to itself
(something that is not impossible but that has various disadvantages in
practice).
We often identify functions with the symbols used to name them. For
example, we often speak of “the function car”, not
distinguishing between the symbol car and the primitive
subr-object that is its function definition. For most purposes, there
is no need to distinguish.
Even so, keep in mind that a function need not have a unique name. While
a given function object usually appears in the function cell of only
one symbol, this is just a matter of convenience. It is easy to store
it in several symbols using fset; then each of the symbols is
equally well a name for the same function.
A symbol used as a function name may also be used as a variable; these two uses of a symbol are independent and do not conflict. (Some Lisp dialects, such as Scheme, do not distinguish between a symbol's value and its function definition; a symbol's value as a variable is also its function definition.) If you have not given a symbol a function definition, you cannot use it as a function; whether the symbol has a value as a variable makes no difference to this.
We usually give a name to a function when it is first created. This
is called defining a function, and it is done with the
defun special form.
defunis the usual way to define new Lisp functions. It defines the symbol name as a function that looks like this:(lambda argument-list . body-forms)
defunstores this lambda expression in the function cell of name. It returns the value name, but usually we ignore this value.As described previously (see Lambda Expressions), argument-list is a list of argument names and may include the keywords
&optionaland&rest. Also, the first two of the body-forms may be a documentation string and an interactive declaration.There is no conflict if the same symbol name is also used as a variable, since the symbol's value cell is independent of the function cell. See Symbol Components.
Here are some examples:
(defun foo () 5) => foo (foo) => 5 (defun bar (a &optional b &rest c) (list a b c)) => bar (bar 1 2 3 4 5) => (1 2 (3 4 5)) (bar 1) => (1 nil nil) (bar) error--> Wrong number of arguments. (defun capitalize-backwards () "Upcase the last letter of a word." (interactive) (backward-word 1) (forward-word 1) (backward-char 1) (capitalize-word 1)) => capitalize-backwardsBe careful not to redefine existing functions unintentionally.
defunredefines even primitive functions such ascarwithout any hesitation or notification. Redefining a function already defined is often done deliberately, and there is no way to distinguish deliberate redefinition from unintentional redefinition.
This special form defines the symbol name as a function, with definition definition (which can be any valid Lisp function).
The proper place to use
defaliasis where a specific function name is being defined—especially where that name appears explicitly in the source file being loaded. This is becausedefaliasrecords which file defined the function, just likedefun(see Unloading).By contrast, in programs that manipulate function definitions for other purposes, it is better to use
fset, which does not keep such records.
See also defsubst, which defines a function like defun
and tells the Lisp compiler to open-code it. See Inline Functions.
Defining functions is only half the battle. Functions don't do anything until you call them, i.e., tell them to run. Calling a function is also known as invocation.
The most common way of invoking a function is by evaluating a list.
For example, evaluating the list (concat "a" "b") calls the
function concat with arguments "a" and "b".
See Evaluation, for a description of evaluation.
When you write a list as an expression in your program, the function
name it calls is written in your program. This means that you choose
which function to call, and how many arguments to give it, when you
write the program. Usually that's just what you want. Occasionally you
need to compute at run time which function to call. To do that, use the
function funcall. When you also need to determine at run time
how many arguments to pass, use apply.
funcallcalls function with arguments, and returns whatever function returns.Since
funcallis a function, all of its arguments, including function, are evaluated beforefuncallis called. This means that you can use any expression to obtain the function to be called. It also means thatfuncalldoes not see the expressions you write for the arguments, only their values. These values are not evaluated a second time in the act of calling function;funcallenters the normal procedure for calling a function at the place where the arguments have already been evaluated.The argument function must be either a Lisp function or a primitive function. Special forms and macros are not allowed, because they make sense only when given the “unevaluated” argument expressions.
funcallcannot provide these because, as we saw above, it never knows them in the first place.(setq f 'list) => list (funcall f 'x 'y 'z) => (x y z) (funcall f 'x 'y '(z)) => (x y (z)) (funcall 'and t nil) error--> Invalid function: #<subr and>Compare these examples with the examples of
apply.
applycalls function with arguments, just likefuncallbut with one difference: the last of arguments is a list of objects, which are passed to function as separate arguments, rather than a single list. We say thatapplyspreads this list so that each individual element becomes an argument.
applyreturns the result of calling function. As withfuncall, function must either be a Lisp function or a primitive function; special forms and macros do not make sense inapply.(setq f 'list) => list (apply f 'x 'y 'z) error--> Wrong type argument: listp, z (apply '+ 1 2 '(3 4)) => 10 (apply '+ '(1 2 3 4)) => 10 (apply 'append '((a b c) nil (x y z) nil)) => (a b c x y z)For an interesting example of using
apply, see the description ofmapcar, in Mapping Functions.
It is common for Lisp functions to accept functions as arguments or
find them in data structures (especially in hook variables and property
lists) and call them using funcall or apply. Functions
that accept function arguments are often called functionals.
Sometimes, when you call a functional, it is useful to supply a no-op function as the argument. Here are two different kinds of no-op function:
A mapping function applies a given function to each element of a
list or other collection. Emacs Lisp has several such functions;
mapcar and mapconcat, which scan a list, are described
here. See Creating Symbols, for the function mapatoms which
maps over the symbols in an obarray. See Hash Access, for the
function maphash which maps over key/value associations in a
hash table.
These mapping functions do not allow char-tables because a char-table
is a sparse array whose nominal range of indices is very large. To map
over a char-table in a way that deals properly with its sparse nature,
use the function map-char-table (see Char-Tables).
mapcarapplies function to each element of sequence in turn, and returns a list of the results.The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string. The result is always a list. The length of the result is the same as the length of sequence.
For example:
(mapcar 'car '((a b) (c d) (e f))) => (a c e) (mapcar '1+ [1 2 3]) => (2 3 4) (mapcar 'char-to-string "abc") => ("a" "b" "c") ;; Call each function inmy-hooks. (mapcar 'funcall my-hooks) (defun mapcar* (function &rest args) "Apply FUNCTION to successive cars of all ARGS. Return the list of results." ;; If no list is exhausted, (if (not (memq 'nil args)) ;; apply function to cars. (cons (apply function (mapcar 'car args)) (apply 'mapcar* function ;; Recurse for rest of elements. (mapcar 'cdr args))))) (mapcar* 'cons '(a b c) '(1 2 3 4)) => ((a . 1) (b . 2) (c . 3))
mapcis likemapcarexcept that function is used for side-effects only—the values it returns are ignored, not collected into a list.mapcalways returns sequence.
mapconcatapplies function to each element of sequence: the results, which must be strings, are concatenated. Between each pair of result strings,mapconcatinserts the string separator. Usually separator contains a space or comma or other suitable punctuation.The argument function must be a function that can take one argument and return a string. The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string.
(mapconcat 'symbol-name '(The cat in the hat) " ") => "The cat in the hat" (mapconcat (function (lambda (x) (format "%c" (1+ x)))) "HAL-8000" "") => "IBM.9111"
In Lisp, a function is a list that starts with lambda, a
byte-code function compiled from such a list, or alternatively a
primitive subr-object; names are “extra”. Although usually functions
are defined with defun and given names at the same time, it is
occasionally more concise to use an explicit lambda expression—an
anonymous function. Such a list is valid wherever a function name is.
Any method of creating such a list makes a valid function. Even this:
(setq silly (append '(lambda (x)) (list (list '+ (* 3 4) 'x))))
=> (lambda (x) (+ 12 x))
This computes a list that looks like (lambda (x) (+ 12 x)) and
makes it the value (not the function definition!) of
silly.
Here is how we might call this function:
(funcall silly 1)
=> 13
(It does not work to write (silly 1), because this function
is not the function definition of silly. We have not given
silly any function definition, just a value as a variable.)
Most of the time, anonymous functions are constants that appear in
your program. For example, you might want to pass one as an argument to
the function mapcar, which applies any given function to each
element of a list.
Here we define a function change-property which
uses a function as its third argument:
(defun change-property (symbol prop function)
(let ((value (get symbol prop)))
(put symbol prop (funcall function value))))
Here we define a function that uses change-property,
passing it a function to double a number:
(defun double-property (symbol prop)
(change-property symbol prop '(lambda (x) (* 2 x))))
In such cases, we usually use the special form function instead
of simple quotation to quote the anonymous function, like this:
(defun double-property (symbol prop)
(change-property symbol prop
(function (lambda (x) (* 2 x)))))
Using function instead of quote makes a difference if you
compile the function double-property. For example, if you
compile the second definition of double-property, the anonymous
function is compiled as well. By contrast, if you compile the first
definition which uses ordinary quote, the argument passed to
change-property is the precise list shown:
(lambda (x) (* x 2))
The Lisp compiler cannot assume this list is a function, even though it
looks like one, since it does not know what change-property will
do with the list. Perhaps it will check whether the car of the third
element is the symbol *! Using function tells the
compiler it is safe to go ahead and compile the constant function.
Nowadays it is possible to omit function entirely, like this:
(defun double-property (symbol prop)
(change-property symbol prop (lambda (x) (* 2 x))))
This is because lambda itself implies function.
We sometimes write function instead of quote when
quoting the name of a function, but this usage is just a sort of
comment:
(function symbol) == (quote symbol) == 'symbol
The read syntax #' is a short-hand for using function.
For example,
#'(lambda (x) (* x x))
is equivalent to
(function (lambda (x) (* x x)))
This special form returns function-object without evaluating it. In this, it is equivalent to
quote. However, it serves as a note to the Emacs Lisp compiler that function-object is intended to be used only as a function, and therefore can safely be compiled. Contrast this withquote, in Quoting.
See documentation in Accessing Documentation, for a
realistic example using function and an anonymous function.
The function definition of a symbol is the object stored in the function cell of the symbol. The functions described here access, test, and set the function cell of symbols.
See also the function indirect-function in Function Indirection.
This returns the object in the function cell of symbol. If the symbol's function cell is void, a
void-functionerror is signaled.This function does not check that the returned object is a legitimate function.
(defun bar (n) (+ n 2)) => bar (symbol-function 'bar) => (lambda (n) (+ n 2)) (fset 'baz 'bar) => bar (symbol-function 'baz) => bar
If you have never given a symbol any function definition, we say that
that symbol's function cell is void. In other words, the function
cell does not have any Lisp object in it. If you try to call such a symbol
as a function, it signals a void-function error.
Note that void is not the same as nil or the symbol
void. The symbols nil and void are Lisp objects,
and can be stored into a function cell just as any other object can be
(and they can be valid functions if you define them in turn with
defun). A void function cell contains no object whatsoever.
You can test the voidness of a symbol's function definition with
fboundp. After you have given a symbol a function definition, you
can make it void once more using fmakunbound.
This function returns
tif the symbol has an object in its function cell,nilotherwise. It does not check that the object is a legitimate function.
This function makes symbol's function cell void, so that a subsequent attempt to access this cell will cause a
void-functionerror. (See alsomakunbound, in Void Variables.)(defun foo (x) x) => foo (foo 1) =>1 (fmakunbound 'foo) => foo (foo 1) error--> Symbol's function definition is void: foo
This function stores definition in the function cell of symbol. The result is definition. Normally definition should be a function or the name of a function, but this is not checked. The argument symbol is an ordinary evaluated argument.
There are three normal uses of this function:
- Copying one symbol's function definition to another—in other words, making an alternate name for a function. (If you think of this as the definition of the new name, you should use
defaliasinstead offset; see Defining Functions.)- Giving a symbol a function definition that is not a list and therefore cannot be made with
defun. For example, you can usefsetto give a symbols1a function definition which is another symbols2; thens1serves as an alias for whatever definitions2presently has. (Once again usedefaliasinstead offsetif you think of this as the definition ofs1.)- In constructs for defining or altering functions. If
defunwere not a primitive, it could be written in Lisp (as a macro) usingfset.Here are examples of these uses:
;; Savefoo's definition inold-foo. (fset 'old-foo (symbol-function 'foo)) ;; Make the symbolcarthe function definition ofxfirst. ;; (Most likely,defaliaswould be better thanfsethere.) (fset 'xfirst 'car) => car (xfirst '(1 2 3)) => 1 (symbol-function 'xfirst) => car (symbol-function (symbol-function 'xfirst)) => #<subr car> ;; Define a named keyboard macro. (fset 'kill-two-lines "\^u2\^k") => "\^u2\^k" ;; Here is a function that alters other functions. (defun copy-function-definition (new old) "Define NEW with the same function definition as OLD." (fset new (symbol-function old)))
When writing a function that extends a previously defined function, the following idiom is sometimes used:
(fset 'old-foo (symbol-function 'foo))
(defun foo ()
"Just like old-foo, except more so."
(old-foo)
(more-so))
This does not work properly if foo has been defined to autoload.
In such a case, when foo calls old-foo, Lisp attempts
to define old-foo by loading a file. Since this presumably
defines foo rather than old-foo, it does not produce the
proper results. The only way to avoid this problem is to make sure the
file is loaded before moving aside the old definition of foo.
But it is unmodular and unclean, in any case, for a Lisp file to redefine a function defined elsewhere. It is cleaner to use the advice facility (see Advising Functions).
You can define an inline function by using defsubst instead
of defun. An inline function works just like an ordinary
function except for one thing: when you compile a call to the function,
the function's definition is open-coded into the caller.
Making a function inline makes explicit calls run faster. But it also has disadvantages. For one thing, it reduces flexibility; if you change the definition of the function, calls already inlined still use the old definition until you recompile them. Since the flexibility of redefining functions is an important feature of Emacs, you should not make a function inline unless its speed is really crucial.
Another disadvantage is that making a large function inline can increase the size of compiled code both in files and in memory. Since the speed advantage of inline functions is greatest for small functions, you generally should not make large functions inline.
It's possible to define a macro to expand into the same code that an
inline function would execute. (See Macros.) But the macro would be
limited to direct use in expressions—a macro cannot be called with
apply, mapcar and so on. Also, it takes some work to
convert an ordinary function into a macro. To convert it into an inline
function is very easy; simply replace defun with defsubst.
Since each argument of an inline function is evaluated exactly once, you
needn't worry about how many times the body uses the arguments, as you
do for macros. (See Argument Evaluation.)
Inline functions can be used and open-coded later on in the same file, following the definition, just like macros.
Here is a table of several functions that do things related to function calling and function definitions. They are documented elsewhere, but we provide cross references here.
applyautoloadcall-interactivelycommandpdocumentationevalfuncallfunctionignoreindirect-functioninteractiveinteractive-pmapatomsmapcarmap-char-tablemapconcatundefinedMacros enable you to define new control constructs and other language features. A macro is defined much like a function, but instead of telling how to compute a value, it tells how to compute another Lisp expression which will in turn compute the value. We call this expression the expansion of the macro.
Macros can do this because they operate on the unevaluated expressions for the arguments, not on the argument values as functions do. They can therefore construct an expansion containing these argument expressions or parts of them.
If you are using a macro to do something an ordinary function could do, just for the sake of speed, consider using an inline function instead. See Inline Functions.
Suppose we would like to define a Lisp construct to increment a
variable value, much like the ++ operator in C. We would like to
write (inc x) and have the effect of (setq x (1+ x)).
Here's a macro definition that does the job:
(defmacro inc (var)
(list 'setq var (list '1+ var)))
When this is called with (inc x), the argument var is the
symbol x—not the value of x, as it would
be in a function. The body of the macro uses this to construct the
expansion, which is (setq x (1+ x)). Once the macro definition
returns this expansion, Lisp proceeds to evaluate it, thus incrementing
x.
A macro call looks just like a function call in that it is a list which starts with the name of the macro. The rest of the elements of the list are the arguments of the macro.
Evaluation of the macro call begins like evaluation of a function call except for one crucial difference: the macro arguments are the actual expressions appearing in the macro call. They are not evaluated before they are given to the macro definition. By contrast, the arguments of a function are results of evaluating the elements of the function call list.
Having obtained the arguments, Lisp invokes the macro definition just
as a function is invoked. The argument variables of the macro are bound
to the argument values from the macro call, or to a list of them in the
case of a &rest argument. And the macro body executes and
returns its value just as a function body does.
The second crucial difference between macros and functions is that the value returned by the macro body is not the value of the macro call. Instead, it is an alternate expression for computing that value, also known as the expansion of the macro. The Lisp interpreter proceeds to evaluate the expansion as soon as it comes back from the macro.
Since the expansion is evaluated in the normal manner, it may contain calls to other macros. It may even be a call to the same macro, though this is unusual.
You can see the expansion of a given macro call by calling
macroexpand.
This function expands form, if it is a macro call. If the result is another macro call, it is expanded in turn, until something which is not a macro call results. That is the value returned by
macroexpand. If form is not a macro call to begin with, it is returned as given.Note that
macroexpanddoes not look at the subexpressions of form (although some macro definitions may do so). Even if they are macro calls themselves,macroexpanddoes not expand them.The function
macroexpanddoes not expand calls to inline functions. Normally there is no need for that, since a call to an inline function is no harder to understand than a call to an ordinary function.If environment is provided, it specifies an alist of macro definitions that shadow the currently defined macros. Byte compilation uses this feature.
(defmacro inc (var) (list 'setq var (list '1+ var))) => inc (macroexpand '(inc r)) => (setq r (1+ r)) (defmacro inc2 (var1 var2) (list 'progn (list 'inc var1) (list 'inc var2))) => inc2 (macroexpand '(inc2 r s)) => (progn (inc r) (inc s)) ;incnot expanded here.
You might ask why we take the trouble to compute an expansion for a macro and then evaluate the expansion. Why not have the macro body produce the desired results directly? The reason has to do with compilation.
When a macro call appears in a Lisp program being compiled, the Lisp compiler calls the macro definition just as the interpreter would, and receives an expansion. But instead of evaluating this expansion, it compiles the expansion as if it had appeared directly in the program. As a result, the compiled code produces the value and side effects intended for the macro, but executes at full compiled speed. This would not work if the macro body computed the value and side effects itself—they would be computed at compile time, which is not useful.
In order for compilation of macro calls to work, the macros must
already be defined in Lisp when the calls to them are compiled. The
compiler has a special feature to help you do this: if a file being
compiled contains a defmacro form, the macro is defined
temporarily for the rest of the compilation of that file. To make this
feature work, you must put the defmacro in the same file where it
is used, and before its first use.
Byte-compiling a file executes any require calls at top-level
in the file. This is in case the file needs the required packages for
proper compilation. One way to ensure that necessary macro definitions
are available during compilation is to require the files that define
them (see Named Features). To avoid loading the macro definition files
when someone runs the compiled program, write
eval-when-compile around the require calls (see Eval During Compile).
A Lisp macro is a list whose car is macro. Its cdr should
be a function; expansion of the macro works by applying the function
(with apply) to the list of unevaluated argument-expressions
from the macro call.
It is possible to use an anonymous Lisp macro just like an anonymous
function, but this is never done, because it does not make sense to pass
an anonymous macro to functionals such as mapcar. In practice,
all Lisp macros have names, and they are usually defined with the
special form defmacro.
defmacrodefines the symbol name as a macro that looks like this:(macro lambda argument-list . body-forms)(Note that the cdr of this list is a function—a lambda expression.) This macro object is stored in the function cell of name. The value returned by evaluating the
defmacroform is name, but usually we ignore this value.The shape and meaning of argument-list is the same as in a function, and the keywords
&restand&optionalmay be used (see Argument List). Macros may have a documentation string, but anyinteractivedeclaration is ignored since macros cannot be called interactively.
Macros often need to construct large list structures from a mixture of constants and nonconstant parts. To make this easier, use the ‘`’ syntax (usually called backquote).
Backquote allows you to quote a list, but selectively evaluate
elements of that list. In the simplest case, it is identical to the
special form quote (see Quoting). For example, these
two forms yield identical results:
`(a list of (+ 2 3) elements)
=> (a list of (+ 2 3) elements)
'(a list of (+ 2 3) elements)
=> (a list of (+ 2 3) elements)
The special marker ‘,’ inside of the argument to backquote indicates a value that isn't constant. Backquote evaluates the argument of ‘,’ and puts the value in the list structure:
(list 'a 'list 'of (+ 2 3) 'elements)
=> (a list of 5 elements)
`(a list of ,(+ 2 3) elements)
=> (a list of 5 elements)
Substitution with ‘,’ is allowed at deeper levels of the list structure also. For example:
(defmacro t-becomes-nil (variable)
`(if (eq ,variable t)
(setq ,variable nil)))
(t-becomes-nil foo)
== (if (eq foo t) (setq foo nil))
You can also splice an evaluated value into the resulting list, using the special marker ‘,@’. The elements of the spliced list become elements at the same level as the other elements of the resulting list. The equivalent code without using ‘`’ is often unreadable. Here are some examples:
(setq some-list '(2 3))
=> (2 3)
(cons 1 (append some-list '(4) some-list))
=> (1 2 3 4 2 3)
`(1 ,@some-list 4 ,@some-list)
=> (1 2 3 4 2 3)
(setq list '(hack foo bar))
=> (hack foo bar)
(cons 'use
(cons 'the
(cons 'words (append (cdr list) '(as elements)))))
=> (use the words foo bar as elements)
`(use the words ,@(cdr list) as elements)
=> (use the words foo bar as elements)
In old Emacs versions, before version 19.29, ‘`’ used a different syntax which required an extra level of parentheses around the entire backquote construct. Likewise, each ‘,’ or ‘,@’ substitution required an extra level of parentheses surrounding both the ‘,’ or ‘,@’ and the following expression. The old syntax required whitespace between the ‘`’, ‘,’ or ‘,@’ and the following expression.
This syntax is still accepted, for compatibility with old Emacs versions, but we recommend not using it in new programs.
The basic facts of macro expansion have counterintuitive consequences. This section describes some important consequences that can lead to trouble, and rules to follow to avoid trouble.
The most common problem in writing macros is doing too some of the real work prematurely—while expanding the macro, rather than in the expansion itself. For instance, one real package had this nmacro definition:
(defmacro my-set-buffer-multibyte (arg)
(if (fboundp 'set-buffer-multibyte)
(set-buffer-multibyte arg)))
With this erroneous macro definition, the program worked fine when
interpreted but failed when compiled. This macro definition called
set-buffer-multibyte during compilation, which was wrong, and
then did nothing when the compiled package was run. The definition
that the programmer really wanted was this:
(defmacro my-set-buffer-multibyte (arg)
(if (fboundp 'set-buffer-multibyte)
`(set-buffer-multibyte ,arg)))
This macro expands, if appropriate, into a call to
set-buffer-multibyte that will be executed when the compiled
program is actually run.
When defining a macro you must pay attention to the number of times the arguments will be evaluated when the expansion is executed. The following macro (used to facilitate iteration) illustrates the problem. This macro allows us to write a simple “for” loop such as one might find in Pascal.
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
(list 'let (list (list var init))
(cons 'while (cons (list '<= var final)
(append body (list (list 'inc var)))))))
=> for
(for i from 1 to 3 do
(setq square (* i i))
(princ (format "\n%d %d" i square)))
==>
(let ((i 1))
(while (<= i 3)
(setq square (* i i))
(princ (format "%d %d" i square))
(inc i)))
-|1 1
-|2 4
-|3 9
=> nil
The arguments from, to, and do in this macro are
“syntactic sugar”; they are entirely ignored. The idea is that you
will write noise words (such as from, to, and do)
in those positions in the macro call.
Here's an equivalent definition simplified through use of backquote:
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
`(let ((,var ,init))
(while (<= ,var ,final)
,@body
(inc ,var))))
Both forms of this definition (with backquote and without) suffer from
the defect that final is evaluated on every iteration. If
final is a constant, this is not a problem. If it is a more
complex form, say (long-complex-calculation x), this can slow
down the execution significantly. If final has side effects,
executing it more than once is probably incorrect.
A well-designed macro definition takes steps to avoid this problem by
producing an expansion that evaluates the argument expressions exactly
once unless repeated evaluation is part of the intended purpose of the
macro. Here is a correct expansion for the for macro:
(let ((i 1)
(max 3))
(while (<= i max)
(setq square (* i i))
(princ (format "%d %d" i square))
(inc i)))
Here is a macro definition that creates this expansion:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
`(let ((,var ,init)
(max ,final))
(while (<= ,var max)
,@body
(inc ,var))))
Unfortunately, this fix introduces another problem, described in the following section.
In the previous section, the definition of for was fixed as
follows to make the expansion evaluate the macro arguments the proper
number of times:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
`(let ((,var ,init)
(max ,final))
(while (<= ,var max)
,@body
(inc ,var))))
The new definition of for has a new problem: it introduces a
local variable named max which the user does not expect. This
causes trouble in examples such as the following:
(let ((max 0))
(for x from 0 to 10 do
(let ((this (frob x)))
(if (< max this)
(setq max this)))))
The references to max inside the body of the for, which
are supposed to refer to the user's binding of max, really access
the binding made by for.
The way to correct this is to use an uninterned symbol instead of
max (see Creating Symbols). The uninterned symbol can be
bound and referred to just like any other symbol, but since it is
created by for, we know that it cannot already appear in the
user's program. Since it is not interned, there is no way the user can
put it into the program later. It will never appear anywhere except
where put by for. Here is a definition of for that works
this way:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
(let ((tempvar (make-symbol "max")))
`(let ((,var ,init)
(,tempvar ,final))
(while (<= ,var ,tempvar)
,@body
(inc ,var)))))
This creates an uninterned symbol named max and puts it in the
expansion instead of the usual interned symbol max that appears
in expressions ordinarily.
Another problem can happen if the macro definition itself
evaluates any of the macro argument expressions, such as by calling
eval (see Eval). If the argument is supposed to refer to the
user's variables, you may have trouble if the user happens to use a
variable with the same name as one of the macro arguments. Inside the
macro body, the macro argument binding is the most local binding of this
variable, so any references inside the form being evaluated do refer to
it. Here is an example:
(defmacro foo (a)
(list 'setq (eval a) t))
=> foo
(setq x 'b)
(foo x) ==> (setq b t)
=> t ; and b has been set.
;; but
(setq a 'c)
(foo a) ==> (setq a t)
=> t ; but this set a, not c.
It makes a difference whether the user's variable is named a or
x, because a conflicts with the macro argument variable
a.
Another problem with calling eval in a macro definition is that
it probably won't do what you intend in a compiled program. The
byte-compiler runs macro definitions while compiling the program, when
the program's own computations (which you might have wished to access
with eval) don't occur and its local variable bindings don't
exist.
To avoid these problems, don't evaluate an argument expression while computing the macro expansion. Instead, substitute the expression into the macro expansion, so that its value will be computed as part of executing the expansion. This is how the other examples in this chapter work.
Occasionally problems result from the fact that a macro call is expanded each time it is evaluated in an interpreted function, but is expanded only once (during compilation) for a compiled function. If the macro definition has side effects, they will work differently depending on how many times the macro is expanded.
Therefore, you should avoid side effects in computation of the macro expansion, unless you really know what you are doing.
One special kind of side effect can't be avoided: constructing Lisp objects. Almost all macro expansions include constructed lists; that is the whole point of most macros. This is usually safe; there is just one case where you must be careful: when the object you construct is part of a quoted constant in the macro expansion.
If the macro is expanded just once, in compilation, then the object is constructed just once, during compilation. But in interpreted execution, the macro is expanded each time the macro call runs, and this means a new object is constructed each time.
In most clean Lisp code, this difference won't matter. It can matter only if you perform side-effects on the objects constructed by the macro definition. Thus, to avoid trouble, avoid side effects on objects constructed by macro definitions. Here is an example of how such side effects can get you into trouble:
(defmacro empty-object ()
(list 'quote (cons nil nil)))
(defun initialize (condition)
(let ((object (empty-object)))
(if condition
(setcar object condition))
object))
If initialize is interpreted, a new list (nil) is
constructed each time initialize is called. Thus, no side effect
survives between calls. If initialize is compiled, then the
macro empty-object is expanded during compilation, producing a
single “constant” (nil) that is reused and altered each time
initialize is called.
One way to avoid pathological cases like this is to think of
empty-object as a funny kind of constant, not as a memory
allocation construct. You wouldn't use setcar on a constant such
as '(nil), so naturally you won't use it on (empty-object)
either.
This chapter describes how to declare user options for customization, and also customization groups for classifying them. We use the term customization item to include both kinds of customization definitions—as well as face definitions (see Defining Faces).
All kinds of customization declarations (for variables and groups, and for faces) accept keyword arguments for specifying various information. This section describes some keywords that apply to all kinds.
All of these keywords, except :tag, can be used more than once
in a given item. Each use of the keyword has an independent effect.
The keyword :tag is an exception because any given item can only
display one name.
:tag label:group group:group in a defgroup, it makes the new group a subgroup of
group.
If you use this keyword more than once, you can put a single item into
more than one group. Displaying any of those groups will show this
item. Please don't overdo this, since the result would be annoying.
:link link-dataThere are three alternatives you can use for link-data:
(custom-manual info-node)"(emacs)Top". The link appears as
‘[manual]’ in the customization buffer.
(info-link info-node)custom-manual except that the link appears
in the customization buffer with the Info node name.
(url-link url)(emacs-commentary-link library)You can specify the text to use in the customization buffer by adding
:tag name after the first element of the link-data;
for example, (info-link :tag "foo" "(emacs)Top") makes a link to
the Emacs manual which appears in the buffer as ‘foo’.
An item can have more than one external link; however, most items have
none at all.
:load fileload-library, and only if the file is
not already loaded.
:require featurerequire.
The most common reason to use :require is when a variable enables
a feature such as a minor mode, and just setting the variable won't have
any effect unless the code which implements the mode is loaded.
Each Emacs Lisp package should have one main customization group which contains all the options, faces and other groups in the package. If the package has a small number of options and faces, use just one group and put everything in it. When there are more than twelve or so options and faces, then you should structure them into subgroups, and put the subgroups under the package's main customization group. It is OK to put some of the options and faces in the package's main group alongside the subgroups.
The package's main or only group should be a member of one or more of
the standard customization groups. (To display the full list of them,
use M-x customize.) Choose one or more of them (but not too
many), and add your group to each of them using the :group
keyword.
The way to declare new customization groups is with defgroup.
Declare group as a customization group containing members. Do not quote the symbol group. The argument doc specifies the documentation string for the group. It should not start with a ‘*’ as in
defcustom; that convention is for variables only.The argument members is a list specifying an initial set of customization items to be members of the group. However, most often members is
nil, and you specify the group's members by using the:groupkeyword when defining those members.If you want to specify group members through members, each element should have the form
(name widget). Here name is a symbol, and widget is a widget type for editing that symbol. Useful widgets arecustom-variablefor a variable,custom-facefor a face, andcustom-groupfor a group.When a new group is introduced into Emacs, use this keyword in
defgroup:
:versionversion- This option specifies that the group was first introduced in Emacs version version. The value version must be a string.
Tag the group with a version like this when it is introduced, rather than the individual members (see Variable Definitions).
In addition to the common keywords (see Common Keywords), you can also use this keyword in
defgroup:
:prefixprefix- If the name of an item in the group starts with prefix, then the tag for that item is constructed (by default) by omitting prefix.
One group can have any number of prefixes.
The prefix-discarding feature is currently turned off, which means
that :prefix currently has no effect. We did this because we
found that discarding the specified prefixes often led to confusing
names for options. This happened because the people who wrote the
defgroup definitions for various groups added :prefix
keywords whenever they make logical sense—that is, whenever the
variables in the library have a common prefix.
In order to obtain good results with :prefix, it would be
necessary to check the specific effects of discarding a particular
prefix, given the specific items in a group and their names and
documentation. If the resulting text is not clear, then :prefix
should not be used in that case.
It should be possible to recheck all the customization groups, delete
the :prefix specifications which give unclear results, and then
turn this feature back on, if someone would like to do the work.
Use defcustom to declare user-editable variables.
Declare option as a customizable user option variable. Do not quote option. The argument doc specifies the documentation string for the variable. It should often start with a ‘*’ to mark it as a user option (see Defining Variables). Do not start the documentation string with ‘*’ for options which cannot or normally should not be set with
set-variable; examples of the former are global minor mode options such asglobal-font-lock-modeand examples of the latter are hooks.If option is void,
defcustominitializes it to default. default should be an expression to compute the value; be careful in writing it, because it can be evaluated on more than one occasion. You should normally avoid using backquotes in default because they are not expanded when editing the value, causing list values to appear to have the wrong structure.When you evaluate a
defcustomform with C-M-x in Emacs Lisp mode (eval-defun), a special feature ofeval-defunarranges to set the variable unconditionally, without testing whether its value is void. (The same feature applies todefvar.) See Defining Variables.
defcustom accepts the following additional keywords:
:type type:options listThis is meaningful only for certain types, currently including
hook, plist and alist. See the definition of the
individual types for a description of how to use :options.
:version version (defcustom foo-max 34
"*Maximum number of foo's allowed."
:type 'integer
:group 'foo
:version "20.3")
:set setfunctionset-default.
:get getfunctiondefault-value.
:initialize functiondefcustom is evaluated. It should take two arguments, the
symbol and value. Here are some predefined functions meant for use in
this way:
custom-initialize-set:set function to initialize the variable, but
do not reinitialize it if it is already non-void. This is the default
:initialize function.
custom-initialize-defaultcustom-initialize-set, but use the function
set-default to set the variable, instead of the variable's
:set function. This is the usual choice for a variable whose
:set function enables or disables a minor mode; with this choice,
defining the variable will not call the minor mode function, but
customizing the variable will do so.
custom-initialize-reset:set function to initialize the variable. If the
variable is already non-void, reset it by calling the :set
function using the current value (returned by the :get method).
custom-initialize-changed:set function to initialize the variable, if it is
already set or has been customized; otherwise, just use
set-default.
:set-after variables:set-after if setting this variable won't work properly unless
those other variables already have their intended values.
The :require option is useful for an option that turns on the
operation of a certain feature. Assuming that the package is coded to
check the value of the option, you still need to arrange for the package
to be loaded. You can do that with :require. See Common Keywords. Here is an example, from the library paren.el:
(defcustom show-paren-mode nil
"Toggle Show Paren mode..."
:set (lambda (symbol value)
(show-paren-mode (or value 0)))
:initialize 'custom-initialize-default
:type 'boolean
:group 'paren-showing
:require 'paren)
If a customization item has a type such as hook or alist,
which supports :options, you can add additional options to the
item, outside the defcustom declaration, by calling
custom-add-option. For example, if you define a function
my-lisp-mode-initialization intended to be called from
emacs-lisp-mode-hook, you might want to add that to the list of
options for emacs-lisp-mode-hook, but not by editing its
definition. You can do it thus:
(custom-add-option 'emacs-lisp-mode-hook
'my-lisp-mode-initialization)
To the customization symbol, add option.
The precise effect of adding option depends on the customization type of symbol.
Internally, defcustom uses the symbol property
standard-value to record the expression for the default value,
and saved-value to record the value saved by the user with the
customization buffer. The saved-value property is actually a
list whose car is an expression which evaluates to the value.
When you define a user option with defcustom, you must specify
its customization type. That is a Lisp object which describes (1)
which values are legitimate and (2) how to display the value in the
customization buffer for editing.
You specify the customization type in defcustom with the
:type keyword. The argument of :type is evaluated; since
types that vary at run time are rarely useful, normally you use a quoted
constant. For example:
(defcustom diff-command "diff"
"*The command to use to run diff."
:type '(string)
:group 'diff)
In general, a customization type is a list whose first element is a symbol, one of the customization type names defined in the following sections. After this symbol come a number of arguments, depending on the symbol. Between the type symbol and its arguments, you can optionally write keyword-value pairs (see Type Keywords).
Some of the type symbols do not use any arguments; those are called
simple types. For a simple type, if you do not use any
keyword-value pairs, you can omit the parentheses around the type
symbol. For example just string as a customization type is
equivalent to (string).
This section describes all the simple customization types.
sexpsexp as a fall-back for any option, if you don't want to
take the time to work out a more specific type to use.
integernumberstringregexpstring except that the string must be a valid regular
expression.
characterfile(file :must-match t)directoryhook:options keyword in a hook variable's
defcustom to specify a list of functions recommended for use in
the hook; see Variable Definitions.
alistYou can specify the key and value types like this:
(alist :key-type key-type :value-type value-type)
where key-type and value-type are customization type
specifications. The default key type is sexp, and the default
value type is sexp.
The user can add any key matching the specified key type, but you can
give some keys a preferential treatment by specifying them with the
:options (see Variable Definitions). The specified keys
will always be shown in the customize buffer (together with a suitable
value), with a checkbox to include or exclude or disable the key/value
pair from the alist. The user will not be able to edit the keys
specified by the :options keyword argument.
The argument to the :options keywords should be a list of option
specifications. Ordinarily, the options are simply atoms, which are the
specified keys. For example:
:options '("foo" "bar" "baz")
specifies that there are three “known” keys, namely "foo",
"bar" and "baz", which will always be shown first.
You may want to restrict the value type for specific keys, for example,
the value associated with the "bar" key can only be an integer.
You can specify this by using a list instead of an atom in the option
specification. The first element will specify the key, like before,
while the second element will specify the value type.
:options '("foo" ("bar" integer) "baz")
Finally, you may want to change how the key is presented. By default,
the key is simply shown as a const, since the user cannot change
the special keys specified with the :options keyword. However,
you may want to use a more specialized type for presenting the key, like
function-item if you know it is a symbol with a function binding.
This is done by using a customization type specification instead of a
symbol for the key.
:options '("foo" ((function-item some-function) integer) "baz")
Many alists use lists with two elements, instead of cons cells. For example,
(defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3))
"Each element is a list of the form (KEY VALUE).")
instead of
(defcustom cons-alist '(("foo" . 1) ("bar" . 2) ("baz" . 3))
"Each element is a cons-cell (KEY . VALUE).")
Because of the way lists are implemented on top of cons cells, you can
treat list-alist in the example above as a cons cell alist, where
the value type is a list with a single element containing the real
value.
(defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3))
"Each element is a list of the form (KEY VALUE)."
:type '(alist :value-type (group integer)))
The group widget is used here instead of list only because
the formatting is better suited for the purpose.
Similarily, you can have alists with more values associated with each key, using variations of this trick:
(defcustom person-data '(("brian" 50 t)
("dorith" 55 nil)
("ken" 52 t))
"Alist of basic info about people.
Each element has the form (NAME AGE MALE-FLAG)."
:type '(alist :value-type (group age boolean)))
(defcustom pets '(("brian")
("dorith" "dog" "guppy")
("ken" "cat"))
"Alist of people's pets.
In an element (KEY . VALUE), KEY is the person's name,
and the VALUE is a list of that person's pets."
:type '(alist :value-type (repeat string)))
plistplist custom type is similar to the alist (see above),
except that the information is stored as a property list, i.e. a list of
this form:
(key value key value key value ...)
The default :key-type for plist is symbol,
rather than sexp.
symbolfunctionvariablefacebooleannil or t. Note that by
using choice and const together (see the next section),
you can specify that the value must be nil or t, but also
specify the text to describe each value in a way that fits the specific
meaning of the alternative.
coding-systemcolorWhen none of the simple types is appropriate, you can use composite types, which build new types from other types. Here are several ways of doing that:
(restricted-sexp :match-alternatives criteria)nil or non-nil according to
the argument. Using a predicate in the list says that objects for which
the predicate returns non-nil are acceptable.
'object. This sort of element
in the list says that object itself is an acceptable value.
For example,
(restricted-sexp :match-alternatives
(integerp 't 'nil))
allows integers, t and nil as legitimate values.
The customization buffer shows all legitimate values using their read
syntax, and the user edits them textually.
(cons car-type cdr-type)(cons string
symbol) is a customization type which matches values such as
("foo" . foo).
In the customization buffer, the car and the cdr are
displayed and edited separately, each according to the type
that you specify for it.
(list element-types...)For example, (list integer string function) describes a list of
three elements; the first element must be an integer, the second a
string, and the third a function.
In the customization buffer, each element is displayed and edited
separately, according to the type specified for it.
(vector element-types...)list except that the value must be a vector instead of a
list. The elements work the same as in list.
(choice alternative-types...)(choice integer string) allows either an
integer or a string.
In the customization buffer, the user selects one of the alternatives using a menu, and can then edit the value in the usual way for that alternative.
Normally the strings in this menu are determined automatically from the
choices; however, you can specify different strings for the menu by
including the :tag keyword in the alternatives. For example, if
an integer stands for a number of spaces, while a string is text to use
verbatim, you might write the customization type this way,
(choice (integer :tag "Number of spaces")
(string :tag "Literal text"))
so that the menu offers ‘Number of spaces’ and ‘Literal Text’.
In any alternative for which nil is not a valid value, other than
a const, you should specify a valid default for that alternative
using the :value keyword. See Type Keywords.
(radio element-types...)choice, except that the choices are displayed
using `radio buttons' rather than a menu. This has the advantage of
displaying documentation for the choices when applicable and so is often
a good choice for a choice between constant functions
(function-item customization types).
(const value)The main use of const is inside of choice. For example,
(choice integer (const nil)) allows either an integer or
nil.
:tag is often used with const, inside of choice.
For example,
(choice (const :tag "Yes" t)
(const :tag "No" nil)
(const :tag "Ask" foo))
describes a variable for which t means yes, nil means no,
and foo means “ask.”
(other value)The main use of other is as the last element of choice.
For example,
(choice (const :tag "Yes" t)
(const :tag "No" nil)
(other :tag "Ask" foo))
describes a variable for which t means yes, nil means no,
and anything else means “ask.” If the user chooses ‘Ask’ from
the menu of alternatives, that specifies the value foo; but any
other value (not t, nil or foo) displays as
‘Ask’, just like foo.
(function-item function)const, but used for values which are functions. This
displays the documentation string as well as the function name.
The documentation string is either the one you specify with
:doc, or function's own documentation string.
(variable-item variable)const, but used for values which are variable names. This
displays the documentation string as well as the variable name. The
documentation string is either the one you specify with :doc, or
variable's own documentation string.
(set types...)This appears in the customization buffer as a checklist, so that each of
types may have either one corresponding element or none. It is
not possible to specify two different elements that match the same one
of types. For example, (set integer symbol) allows one
integer and/or one symbol in the list; it does not allow multiple
integers or multiple symbols. As a result, it is rare to use
nonspecific types such as integer in a set.
Most often, the types in a set are const types, as
shown here:
(set (const :bold) (const :italic))
Sometimes they describe possible elements in an alist:
(set (cons :tag "Height" (const height) integer)
(cons :tag "Width" (const width) integer))
That lets the user specify a height value optionally
and a width value optionally.
(repeat element-type)The :inline feature lets you splice a variable number of
elements into the middle of a list or vector. You use it in a
set, choice or repeat type which appears among the
element-types of a list or vector.
Normally, each of the element-types in a list or vector
describes one and only one element of the list or vector. Thus, if an
element-type is a repeat, that specifies a list of unspecified
length which appears as one element.
But when the element-type uses :inline, the value it matches is
merged directly into the containing sequence. For example, if it
matches a list with three elements, those become three elements of the
overall sequence. This is analogous to using ‘,@’ in the backquote
construct.
For example, to specify a list whose first element must be t
and whose remaining arguments should be zero or more of foo and
bar, use this customization type:
(list (const t) (set :inline t foo bar))
This matches values such as (t), (t foo), (t bar)
and (t foo bar).
When the element-type is a choice, you use :inline not
in the choice itself, but in (some of) the alternatives of the
choice. For example, to match a list which must start with a
file name, followed either by the symbol t or two strings, use
this customization type:
(list file
(choice (const t)
(list :inline t string string)))
If the user chooses the first alternative in the choice, then the
overall list has two elements and the second element is t. If
the user chooses the second alternative, then the overall list has three
elements and the second and third must be strings.
You can specify keyword-argument pairs in a customization type after the type name symbol. Here are the keywords you can use, and their meanings:
:value defaultchoice; it specifies the default value to use, at first, if and
when the user selects this alternative with the menu in the
customization buffer.
Of course, if the actual value of the option fits this alternative, it will appear showing the actual value, not default.
If nil is not a valid value for the alternative, then it is
essential to specify a valid default with :value.
:format format-string:action
attribute specifies what the button will do if the user invokes it;
its value is a function which takes two arguments—the widget which
the button appears in, and the event.
There is no way to specify two different buttons with different
actions.
:sample-face.
:tag
keyword.
:action action:button-face face:button-prefix prefix:button-suffix suffixnil:tag tag:doc doc:format, and use ‘%d’ or ‘%h’
in that value.
The usual reason to specify a documentation string for a type is to
provide more information about the meanings of alternatives inside a
:choice type or the parts of some other composite type.
:help-echo motion-docwidget-forward or
widget-backward, it will display the string motion-doc in
the echo area. In addition, motion-doc is used as the mouse
help-echo string and may actually be a function or form evaluated
to yield a help string as for help-echo text properties.
:match functionnil if
the value is acceptable.
Loading a file of Lisp code means bringing its contents into the Lisp environment in the form of Lisp objects. Emacs finds and opens the file, reads the text, evaluates each form, and then closes the file.
The load functions evaluate all the expressions in a file just
as the eval-current-buffer function evaluates all the
expressions in a buffer. The difference is that the load functions
read and evaluate the text in the file as found on disk, not the text
in an Emacs buffer.
The loaded file must contain Lisp expressions, either as source code or as byte-compiled code. Each form in the file is called a top-level form. There is no special format for the forms in a loadable file; any form in a file may equally well be typed directly into a buffer and evaluated there. (Indeed, most code is tested this way.) Most often, the forms are function definitions and variable definitions.
A file containing Lisp code is often called a library. Thus, the “Rmail library” is a file containing code for Rmail mode. Similarly, a “Lisp library directory” is a directory of files containing Lisp code.
Emacs Lisp has several interfaces for loading. For example,
autoload creates a placeholder object for a function defined in a
file; trying to call the autoloading function loads the file to get the
function's real definition (see Autoload). require loads a
file if it isn't already loaded (see Named Features). Ultimately,
all these facilities call the load function to do the work.
This function finds and opens a file of Lisp code, evaluates all the forms in it, and closes the file.
To find the file,
loadfirst looks for a file named filename.elc, that is, for a file whose name is filename with ‘.elc’ appended. If such a file exists, it is loaded. If there is no file by that name, thenloadlooks for a file named filename.el. If that file exists, it is loaded. Finally, if neither of those names is found,loadlooks for a file named filename with nothing appended, and loads it if it exists. (Theloadfunction is not clever about looking at filename. In the perverse case of a file named foo.el.el, evaluation of(load "foo.el")will indeed find it.)If the optional argument nosuffix is non-
nil, then the suffixes ‘.elc’ and ‘.el’ are not tried. In this case, you must specify the precise file name you want. By specifying the precise file name and usingtfor nosuffix, you can prevent perverse file names such as foo.el.el from being tried.If the optional argument must-suffix is non-
nil, thenloadinsists that the file name used must end in either ‘.el’ or ‘.elc’, unless it contains an explicit directory name. If filename does not contain an explicit directory name, and does not end in a suffix, thenloadinsists on adding one.If filename is a relative file name, such as foo or baz/foo.bar,
loadsearches for the file using the variableload-path. It appends filename to each of the directories listed inload-path, and loads the first file it finds whose name matches. The current default directory is tried only if it is specified inload-path, wherenilstands for the default directory.loadtries all three possible suffixes in the first directory inload-path, then all three suffixes in the second directory, and so on. See Library Search.If you get a warning that foo.elc is older than foo.el, it means you should consider recompiling foo.el. See Byte Compilation.
When loading a source file (not compiled),
loadperforms character set translation just as Emacs would do when visiting the file. See Coding Systems.Messages like ‘Loading foo...’ and ‘Loading foo...done’ appear in the echo area during loading unless nomessage is non-
nil.Any unhandled errors while loading a file terminate loading. If the load was done for the sake of
autoload, any function definitions made during the loading are undone.If
loadcan't find the file to load, then normally it signals the errorfile-error(with ‘Cannot open load file filename’). But if missing-ok is non-nil, thenloadjust returnsnil.You can use the variable
load-read-functionto specify a function forloadto use instead ofreadfor reading expressions. See below.
loadreturnstif the file loads successfully.
This command loads the file filename. If filename is a relative file name, then the current default directory is assumed.
load-pathis not used, and suffixes are not appended. Use this command if you wish to specify precisely the file name to load.
This command loads the library named library. It is equivalent to
load, except in how it reads its argument interactively.
This variable is non-
nilif Emacs is in the process of loading a file, and it isnilotherwise.
This variable specifies an alternate expression-reading function for
loadandeval-regionto use instead ofread. The function should accept one argument, just asreaddoes.Normally, the variable's value is
nil, which means those functions should useread.Note: Instead of using this variable, it is cleaner to use another, newer feature: to pass the function as the read-function argument to
eval-region. See Eval.
For information about how load is used in building Emacs, see
Building Emacs.
When Emacs loads a Lisp library, it searches for the library
in a list of directories specified by the variable load-path.
The value of this variable is a list of directories to search when loading files with
load. Each element is a string (which must be a directory name) ornil(which stands for the current working directory).
The value of load-path is initialized from the environment
variable EMACSLOADPATH, if that exists; otherwise its default
value is specified in emacs/src/paths.h when Emacs is built.
Then the list is expanded by adding subdirectories of the directories
in the list.
The syntax of EMACSLOADPATH is the same as used for PATH;
‘:’ (or ‘;’, according to the operating system) separates
directory names, and ‘.’ is used for the current default directory.
Here is an example of how to set your EMACSLOADPATH variable from
a csh .login file:
setenv EMACSLOADPATH .:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp
Here is how to set it using sh:
export EMACSLOADPATH
EMACSLOADPATH=.:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp
Here is an example of code you can place in your init file (see Init File) to add several directories to the front of your default
load-path:
(setq load-path
(append (list nil "/user/bil/emacs"
"/usr/local/lisplib"
"~/emacs")
load-path))
In this example, the path searches the current working directory first, followed then by the /user/bil/emacs directory, the /usr/local/lisplib directory, and the ~/emacs directory, which are then followed by the standard directories for Lisp code.
Dumping Emacs uses a special value of load-path. If the value of
load-path at the end of dumping is unchanged (that is, still the
same special value), the dumped Emacs switches to the ordinary
load-path value when it starts up, as described above. But if
load-path has any other value at the end of dumping, that value
is used for execution of the dumped Emacs also.
Therefore, if you want to change load-path temporarily for
loading a few libraries in site-init.el or site-load.el,
you should bind load-path locally with let around the
calls to load.
The default value of load-path, when running an Emacs which has
been installed on the system, includes two special directories (and
their subdirectories as well):
"/usr/local/share/emacs/version/site-lisp"
and
"/usr/local/share/emacs/site-lisp"
The first one is for locally installed packages for a particular Emacs version; the second is for locally installed packages meant for use with all installed Emacs versions.
There are several reasons why a Lisp package that works well in one Emacs version can cause trouble in another. Sometimes packages need updating for incompatible changes in Emacs; sometimes they depend on undocumented internal Emacs data that can change without notice; sometimes a newer Emacs version incorporates a version of the package, and should be used only with that version.
Emacs finds these directories' subdirectories and adds them to
load-path when it starts up. Both immediate subdirectories and
subdirectories multiple levels down are added to load-path.
Not all subdirectories are included, though. Subdirectories whose names do not start with a letter or digit are excluded. Subdirectories named RCS or CVS are excluded. Also, a subdirectory which contains a file named .nosearch is excluded. You can use these methods to prevent certain subdirectories of the site-lisp directories from being searched.
If you run Emacs from the directory where it was built—that is, an
executable that has not been formally installed—then load-path
normally contains two additional directories. These are the lisp
and site-lisp subdirectories of the main build directory. (Both
are represented as absolute file names.)
This command finds the precise file name for library library. It searches for the library in the same way
loaddoes, and the argument nosuffix has the same meaning as inload: don't add suffixes ‘.elc’ or ‘.el’ to the specified name library.If the path is non-
nil, that list of directories is used instead ofload-path.When
locate-libraryis called from a program, it returns the file name as a string. When the user runslocate-libraryinteractively, the argument interactive-call ist, and this tellslocate-libraryto display the file name in the echo area.
When Emacs Lisp programs contain string constants with non-ascii characters, these can be represented within Emacs either as unibyte strings or as multibyte strings (see Text Representations). Which representation is used depends on how the file is read into Emacs. If it is read with decoding into multibyte representation, the text of the Lisp program will be multibyte text, and its string constants will be multibyte strings. If a file containing Latin-1 characters (for example) is read without decoding, the text of the program will be unibyte text, and its string constants will be unibyte strings. See Coding Systems.
To make the results more predictable, Emacs always performs decoding into the multibyte representation when loading Lisp files, even if it was started with the ‘--unibyte’ option. This means that string constants with non-ascii characters translate into multibyte strings. The only exception is when a particular file specifies no decoding.
The reason Emacs is designed this way is so that Lisp programs give
predictable results, regardless of how Emacs was started. In addition,
this enables programs that depend on using multibyte text to work even
in a unibyte Emacs. Of course, such programs should be designed to
notice whether the user prefers unibyte or multibyte text, by checking
default-enable-multibyte-characters, and convert representations
appropriately.
In most Emacs Lisp programs, the fact that non-ascii strings are
multibyte strings should not be noticeable, since inserting them in
unibyte buffers converts them to unibyte automatically. However, if
this does make a difference, you can force a particular Lisp file to be
interpreted as unibyte by writing ‘-*-unibyte: t;-*-’ in a
comment on the file's first line. With that designator, the file will
unconditionally be interpreted as unibyte, even in an ordinary
multibyte Emacs session. This can matter when making keybindings to
non-ascii characters written as ?vliteral.
The autoload facility allows you to make a function or macro known in Lisp, but put off loading the file that defines it. The first call to the function automatically reads the proper file to install the real definition and other associated code, then runs the real definition as if it had been loaded all along.
There are two ways to set up an autoloaded function: by calling
autoload, and by writing a special “magic” comment in the
source before the real definition. autoload is the low-level
primitive for autoloading; any Lisp program can call autoload at
any time. Magic comments are the most convenient way to make a function
autoload, for packages installed along with Emacs. These comments do
nothing on their own, but they serve as a guide for the command
update-file-autoloads, which constructs calls to autoload
and arranges to execute them when Emacs is built.
This function defines the function (or macro) named function so as to load automatically from filename. The string filename specifies the file to load to get the real definition of function.
If filename does not contain either a directory name, or the suffix
.elor.elc, thenautoloadinsists on adding one of these suffixes, and it will not load from a file whose name is just filename with no added suffix.The argument docstring is the documentation string for the function. Normally, this should be identical to the documentation string in the function definition itself. Specifying the documentation string in the call to
autoloadmakes it possible to look at the documentation without loading the function's real definition.If interactive is non-
nil, that says function can be called interactively. This lets completion in M-x work without loading function's real definition. The complete interactive specification is not given here; it's not needed unless the user actually calls function, and when that happens, it's time to load the real definition.You can autoload macros and keymaps as well as ordinary functions. Specify type as
macroif function is really a macro. Specify type askeymapif function is really a keymap. Various parts of Emacs need to know this information without loading the real definition.An autoloaded keymap loads automatically during key lookup when a prefix key's binding is the symbol function. Autoloading does not occur for other kinds of access to the keymap. In particular, it does not happen when a Lisp program gets the keymap from the value of a variable and calls
define-key; not even if the variable name is the same symbol function.If function already has a non-void function definition that is not an autoload object,
autoloaddoes nothing and returnsnil. If the function cell of function is void, or is already an autoload object, then it is defined as an autoload object like this:(autoload filename docstring interactive type)For example,
(symbol-function 'run-prolog) => (autoload "prolog" 169681 t nil)In this case,
"prolog"is the name of the file to load, 169681 refers to the documentation string in the emacs/etc/DOC-version file (see Documentation Basics),tmeans the function is interactive, andnilthat it is not a macro or a keymap.
The autoloaded file usually contains other definitions and may require
or provide one or more features. If the file is not completely loaded
(due to an error in the evaluation of its contents), any function
definitions or provide calls that occurred during the load are
undone. This is to ensure that the next attempt to call any function
autoloading from this file will try again to load the file. If not for
this, then some of the functions in the file might be defined by the
aborted load, but fail to work properly for the lack of certain
subroutines not loaded successfully because they come later in the file.
If the autoloaded file fails to define the desired Lisp function or
macro, then an error is signaled with data "Autoloading failed to
define function function-name".
A magic autoload comment consists of ‘;;;###autoload’, on a line
by itself, just before the real definition of the function in its
autoloadable source file. The command M-x update-file-autoloads
writes a corresponding autoload call into loaddefs.el.
Building Emacs loads loaddefs.el and thus calls autoload.
M-x update-directory-autoloads is even more powerful; it updates
autoloads for all files in the current directory.
The same magic comment can copy any kind of form into
loaddefs.el. If the form following the magic comment is not a
function-defining form or a defcustom form, it is copied
verbatim. “Function-defining forms” include define-skeleton,
define-derived-mode, define-generic-mode and
define-minor-mode as well as defun and
defmacro. To save space, a defcustom form is converted to
a defvar in loaddefs.el, with some additional information
if it uses :require.
You can also use a magic comment to execute a form at build time without executing it when the file itself is loaded. To do this, write the form on the same line as the magic comment. Since it is in a comment, it does nothing when you load the source file; but M-x update-file-autoloads copies it to loaddefs.el, where it is executed while building Emacs.
The following example shows how doctor is prepared for
autoloading with a magic comment:
;;;###autoload
(defun doctor ()
"Switch to *doctor* buffer and start giving psychotherapy."
(interactive)
(switch-to-buffer "*doctor*")
(doctor-mode))
Here's what that produces in loaddefs.el:
(autoload 'doctor "doctor" "\
Switch to *doctor* buffer and start giving psychotherapy."
t)
The backslash and newline immediately following the double-quote are a
convention used only in the preloaded uncompiled Lisp files such as
loaddefs.el; they tell make-docfile to put the
documentation string in the etc/DOC file. See Building Emacs.
See also the commentary in lib-src/make-docfile.c.
You can load a given file more than once in an Emacs session. For example, after you have rewritten and reinstalled a function definition by editing it in a buffer, you may wish to return to the original version; you can do this by reloading the file it came from.
When you load or reload files, bear in mind that the load and
load-library functions automatically load a byte-compiled file
rather than a non-compiled file of similar name. If you rewrite a file
that you intend to save and reinstall, you need to byte-compile the new
version; otherwise Emacs will load the older, byte-compiled file instead
of your newer, non-compiled file! If that happens, the message
displayed when loading the file includes, ‘(compiled; note, source is
newer)’, to remind you to recompile it.
When writing the forms in a Lisp library file, keep in mind that the
file might be loaded more than once. For example, think about whether
each variable should be reinitialized when you reload the library;
defvar does not change the value if the variable is already
initialized. (See Defining Variables.)
The simplest way to add an element to an alist is like this:
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist))
But this would add multiple elements if the library is reloaded. To avoid the problem, write this:
(or (assq 'leif-mode minor-mode-alist)
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist)))
To add an element to a list just once, you can also use add-to-list
(see Setting Variables).
Occasionally you will want to test explicitly whether a library has already been loaded. Here's one way to test, in a library, whether it has been loaded before:
(defvar foo-was-loaded nil)
(unless foo-was-loaded
execute-first-time-only
(setq foo-was-loaded t))
If the library uses provide to provide a named feature, you can
use featurep earlier in the file to test whether the
provide call has been executed before.
See Named Features.
provide and require are an alternative to
autoload for loading files automatically. They work in terms of
named features. Autoloading is triggered by calling a specific
function, but a feature is loaded the first time another program asks
for it by name.
A feature name is a symbol that stands for a collection of functions, variables, etc. The file that defines them should provide the feature. Another program that uses them may ensure they are defined by requiring the feature. This loads the file of definitions if it hasn't been loaded already.
To require the presence of a feature, call require with the
feature name as argument. require looks in the global variable
features to see whether the desired feature has been provided
already. If not, it loads the feature from the appropriate file. This
file should call provide at the top level to add the feature to
features; if it fails to do so, require signals an error.
For example, in emacs/lisp/prolog.el,
the definition for run-prolog includes the following code:
(defun run-prolog ()
"Run an inferior Prolog process, with I/O via buffer *prolog*."
(interactive)
(require 'comint)
(switch-to-buffer (make-comint "prolog" prolog-program-name))
(inferior-prolog-mode))
The expression (require 'comint) loads the file comint.el
if it has not yet been loaded. This ensures that make-comint is
defined. Features are normally named after the files that provide them,
so that require need not be given the file name.
The comint.el file contains the following top-level expression:
(provide 'comint)
This adds comint to the global features list, so that
(require 'comint) will henceforth know that nothing needs to be
done.
When require is used at top level in a file, it takes effect
when you byte-compile that file (see Byte Compilation) as well as
when you load it. This is in case the required package contains macros
that the byte compiler must know about. It also avoids byte-compiler
warnings for functions and variables defined in the file loaded with
require.
Although top-level calls to require are evaluated during
byte compilation, provide calls are not. Therefore, you can
ensure that a file of definitions is loaded before it is byte-compiled
by including a provide followed by a require for the same
feature, as in the following example.
(provide 'my-feature) ; Ignored by byte compiler,
; evaluated by load.
(require 'my-feature) ; Evaluated by byte compiler.
The compiler ignores the provide, then processes the
require by loading the file in question. Loading the file does
execute the provide call, so the subsequent require call
does nothing when the file is loaded.
This function announces that feature is now loaded, or being loaded, into the current Emacs session. This means that the facilities associated with feature are or will be available for other Lisp programs.
The direct effect of calling
provideis to add feature to the front of the listfeaturesif it is not already in the list. The argument feature must be a symbol.providereturns feature.features => (bar bish) (provide 'foo) => foo features => (foo bar bish)When a file is loaded to satisfy an autoload, and it stops due to an error in the evaluating its contents, any function definitions or
providecalls that occurred during the load are undone. See Autoload.
This function checks whether feature is present in the current Emacs session (using
(featurepfeature); see below). The argument feature must be a symbol.If the feature is not present, then
requireloads filename withload. If filename is not supplied, then the name of the symbol feature is used as the base file name to load. However, in this case,requireinsists on finding feature with an added suffix; a file whose name is just feature won't be used.If loading the file fails to provide feature,
requiresignals an error, ‘Required feature feature was not provided’, unless noerror is non-nil.
This function returns
tif feature has been provided in the current Emacs session (i.e., if feature is a member offeatures.)
The value of this variable is a list of symbols that are the features loaded in the current Emacs session. Each symbol was put in this list with a call to
provide. The order of the elements in thefeatureslist is not significant.
You can discard the functions and variables loaded by a library to
reclaim memory for other Lisp objects. To do this, use the function
unload-feature:
This command unloads the library that provided feature feature. It undefines all functions, macros, and variables defined in that library with
defun,defalias,defsubst,defmacro,defconst,defvar, anddefcustom. It then restores any autoloads formerly associated with those symbols. (Loading saves these in theautoloadproperty of the symbol.)Before restoring the previous definitions,
unload-featurerunsremove-hookto remove functions in the library from certain hooks. These hooks include variables whose names end in ‘hook’ or ‘-hooks’, plus those listed inloadhist-special-hooks. This is to prevent Emacs from ceasing to function because important hooks refer to functions that are no longer defined.If these measures are not sufficient to prevent malfunction, a library can define an explicit unload hook. If feature
-unload-hookis defined, it is run as a normal hook before restoring the previous definitions, instead of the usual hook-removing actions. The unload hook ought to undo all the global state changes made by the library that might cease to work once the library is unloaded.unload-featurecan cause problems with libraries that fail to do this, so it should be used with caution.Ordinarily,
unload-featurerefuses to unload a library on which other loaded libraries depend. (A library a depends on library b if a contains arequirefor b.) If the optional argument force is non-nil, dependencies are ignored and you can unload any library.
The unload-feature function is written in Lisp; its actions are
based on the variable load-history.
This variable's value is an alist connecting library names with the names of functions and variables they define, the features they provide, and the features they require.
Each element is a list and describes one library. The car of the list is the name of the library, as a string. The rest of the list is composed of these kinds of objects:
- Symbols that were defined by this library.
- Cons cells of the form
(require .feature)indicating features that were required.- Cons cells of the form
(provide .feature)indicating features that were provided.The value of
load-historymay have one element whose car isnil. This element describes definitions made witheval-bufferon a buffer that is not visiting a file.
The command eval-region updates load-history, but does so
by adding the symbols defined to the element for the file being visited,
rather than replacing that element. See Eval.
Preloaded libraries don't contribute initially to load-history.
Instead, preloading writes information about preloaded libraries into a
file, which can be loaded later on to add information to
load-history describing the preloaded files. This file is
installed in exec-directory and has a name of the form
fns-emacsversion.el.
See the source for the function symbol-file, for an example of
code that loads this file to find functions in preloaded libraries.
This variable holds a list of hooks to be scanned before unloading a library, to remove functions defined in the library.
You can ask for code to be executed if and when a particular library is
loaded, by calling eval-after-load.
This function arranges to evaluate form at the end of loading the library library, if and when library is loaded. If library is already loaded, it evaluates form right away.
The library name library must exactly match the argument of
load. To get the proper results when an installed library is found by searchingload-path, you should not include any directory names in library.An error in form does not undo the load, but does prevent execution of the rest of form.
In general, well-designed Lisp programs should not use this feature.
The clean and modular ways to interact with a Lisp library are (1)
examine and set the library's variables (those which are meant for
outside use), and (2) call the library's functions. If you wish to
do (1), you can do it immediately—there is no need to wait for when
the library is loaded. To do (2), you must load the library (preferably
with require).
But it is OK to use eval-after-load in your personal
customizations if you don't feel they must meet the design standards for
programs meant for wider use.
This variable holds an alist of expressions to evaluate if and when particular libraries are loaded. Each element looks like this:
(filename forms...)The function
loadchecksafter-load-alistin order to implementeval-after-load.
Emacs Lisp has a compiler that translates functions written in Lisp into a special representation called byte-code that can be executed more efficiently. The compiler replaces Lisp function definitions with byte-code. When a byte-code function is called, its definition is evaluated by the byte-code interpreter.
Because the byte-compiled code is evaluated by the byte-code interpreter, instead of being executed directly by the machine's hardware (as true compiled code is), byte-code is completely transportable from machine to machine without recompilation. It is not, however, as fast as true compiled code.
Compiling a Lisp file with the Emacs byte compiler always reads the file as multibyte text, even if Emacs was started with ‘--unibyte’, unless the file specifies otherwise. This is so that compilation gives results compatible with running the same file without compilation. See Loading Non-ASCII.
In general, any version of Emacs can run byte-compiled code produced by recent earlier versions of Emacs, but the reverse is not true. A major incompatible change was introduced in Emacs version 19.29, and files compiled with versions since that one will definitely not run in earlier versions unless you specify a special option. In addition, the modifier bits in keyboard characters were renumbered in Emacs 19.29; as a result, files compiled in versions before 19.29 will not work in subsequent versions if they contain character constants with modifier bits.
See Compilation Errors, for how to investigate errors occurring in byte compilation.
A byte-compiled function is not as efficient as a primitive function written in C, but runs much faster than the version written in Lisp. Here is an example:
(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
=> silly-loop
(silly-loop 100000)
=> ("Fri Mar 18 17:25:57 1994"
"Fri Mar 18 17:26:28 1994") ; 31 seconds
(byte-compile 'silly-loop)
=> [Compiled code not shown]
(silly-loop 100000)
=> ("Fri Mar 18 17:26:52 1994"
"Fri Mar 18 17:26:58 1994") ; 6 seconds
In this example, the interpreted code required 31 seconds to run, whereas the byte-compiled code required 6 seconds. These results are representative, but actual results will vary greatly.
You can byte-compile an individual function or macro definition with
the byte-compile function. You can compile a whole file with
byte-compile-file, or several files with
byte-recompile-directory or batch-byte-compile.
The byte compiler produces error messages and warnings about each file in a buffer called ‘*Compile-Log*’. These report things in your program that suggest a problem but are not necessarily erroneous.
Be careful when writing macro calls in files that you may someday byte-compile. Macro calls are expanded when they are compiled, so the macros must already be defined for proper compilation. For more details, see Compiling Macros. If a program does not work the same way when compiled as it does when interpreted, erroneous macro definitions are one likely cause (see Problems with Macros).
Normally, compiling a file does not evaluate the file's contents or
load the file. But it does execute any require calls at top
level in the file. One way to ensure that necessary macro definitions
are available during compilation is to require the file that defines
them (see Named Features). To avoid loading the macro definition files
when someone runs the compiled program, write
eval-when-compile around the require calls (see Eval During Compile).
This function byte-compiles the function definition of symbol, replacing the previous definition with the compiled one. The function definition of symbol must be the actual code for the function; i.e., the compiler does not follow indirection to another symbol.
byte-compilereturns the new, compiled definition of symbol.If symbol's definition is a byte-code function object,
byte-compiledoes nothing and returnsnil. Lisp records only one function definition for any symbol, and if that is already compiled, non-compiled code is not available anywhere. So there is no way to “compile the same definition again.”(defun factorial (integer) "Compute factorial of INTEGER." (if (= 1 integer) 1 (* integer (factorial (1- integer))))) => factorial (byte-compile 'factorial) => #[(integer) "^H\301U\203^H^@\301\207\302^H\303^HS!\"\207" [integer 1 * factorial] 4 "Compute factorial of INTEGER."]The result is a byte-code function object. The string it contains is the actual byte-code; each character in it is an instruction or an operand of an instruction. The vector contains all the constants, variable names and function names used by the function, except for certain primitives that are coded as special instructions.
This command reads the defun containing point, compiles it, and evaluates the result. If you use this on a defun that is actually a function definition, the effect is to install a compiled version of that function.
This function compiles a file of Lisp code named filename into a file of byte-code. The output file's name is made by changing the ‘.el’ suffix into ‘.elc’; if filename does not end in ‘.el’, it adds ‘.elc’ to the end of filename.
Compilation works by reading the input file one form at a time. If it is a definition of a function or macro, the compiled function or macro definition is written out. Other forms are batched together, then each batch is compiled, and written so that its compiled code will be executed when the file is read. All comments are discarded when the input file is read.
This command returns
t. When called interactively, it prompts for the file name.% ls -l push* -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el (byte-compile-file "~/emacs/push.el") => t % ls -l push* -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el -rw-rw-rw- 1 lewis 638 Oct 8 20:25 push.elc
This function recompiles every ‘.el’ file in directory that needs recompilation. A file needs recompilation if a ‘.elc’ file exists but is older than the ‘.el’ file.
When a ‘.el’ file has no corresponding ‘.elc’ file, flag says what to do. If it is
nil, these files are ignored. If it is non-nil, the user is asked whether to compile each such file.The returned value of this command is unpredictable.
This function runs
byte-compile-fileon files specified on the command line. This function must be used only in a batch execution of Emacs, as it kills Emacs on completion. An error in one file does not prevent processing of subsequent files, but no output file will be generated for it, and the Emacs process will terminate with a nonzero status code.% emacs -batch -f batch-byte-compile *.el
This function actually interprets byte-code. A byte-compiled function is actually defined with a body that calls
byte-code. Don't call this function yourself—only the byte compiler knows how to generate valid calls to this function.In Emacs version 18, byte-code was always executed by way of a call to the function
byte-code. Nowadays, byte-code is usually executed as part of a byte-code function object, and only rarely through an explicit call tobyte-code.
Functions and variables loaded from a byte-compiled file access their documentation strings dynamically from the file whenever needed. This saves space within Emacs, and makes loading faster because the documentation strings themselves need not be processed while loading the file. Actual access to the documentation strings becomes slower as a result, but this normally is not enough to bother users.
Dynamic access to documentation strings does have drawbacks:
If your site installs Emacs following the usual procedures, these problems will never normally occur. Installing a new version uses a new directory with a different name; as long as the old version remains installed, its files will remain unmodified in the places where they are expected to be.
However, if you have built Emacs yourself and use it from the directory where you built it, you will experience this problem occasionally if you edit and recompile Lisp files. When it happens, you can cure the problem by reloading the file after recompiling it.
Byte-compiled files made with recent versions of Emacs (since 19.29)
will not load into older versions because the older versions don't
support this feature. You can turn off this feature at compile time by
setting byte-compile-dynamic-docstrings to nil; then you
can compile files that will load into older Emacs versions. You can do
this globally, or for one source file by specifying a file-local binding
for the variable. One way to do that is by adding this string to the
file's first line:
-*-byte-compile-dynamic-docstrings: nil;-*-
If this is non-
nil, the byte compiler generates compiled files that are set up for dynamic loading of documentation strings.
The dynamic documentation string feature writes compiled files that use a special Lisp reader construct, ‘#@count’. This construct skips the next count characters. It also uses the ‘#$’ construct, which stands for “the name of this file, as a string.” It is usually best not to use these constructs in Lisp source files, since they are not designed to be clear to humans reading the file.
When you compile a file, you can optionally enable the dynamic function loading feature (also known as lazy loading). With dynamic function loading, loading the file doesn't fully read the function definitions in the file. Instead, each function definition contains a place-holder which refers to the file. The first time each function is called, it reads the full definition from the file, to replace the place-holder.
The advantage of dynamic function loading is that loading the file becomes much faster. This is a good thing for a file which contains many separate user-callable functions, if using one of them does not imply you will probably also use the rest. A specialized mode which provides many keyboard commands often has that usage pattern: a user may invoke the mode, but use only a few of the commands it provides.
The dynamic loading feature has certain disadvantages:
These problems will never happen in normal circumstances with installed Emacs files. But they are quite likely to happen with Lisp files that you are changing. The easiest way to prevent these problems is to reload the new compiled file immediately after each recompilation.
The byte compiler uses the dynamic function loading feature if the
variable byte-compile-dynamic is non-nil at compilation
time. Do not set this variable globally, since dynamic loading is
desirable only for certain files. Instead, enable the feature for
specific source files with file-local variable bindings. For example,
you could do it by writing this text in the source file's first line:
-*-byte-compile-dynamic: t;-*-
If this is non-
nil, the byte compiler generates compiled files that are set up for dynamic function loading.
This immediately finishes loading the definition of function from its byte-compiled file, if it is not fully loaded already. The argument function may be a byte-code function object or a function name.
These features permit you to write code to be evaluated during compilation of a program.
This form marks body to be evaluated both when you compile the containing code and when you run it (whether compiled or not).
You can get a similar result by putting body in a separate file and referring to that file with
require. That method is preferable when body is large.
This form marks body to be evaluated at compile time but not when the compiled program is loaded. The result of evaluation by the compiler becomes a constant which appears in the compiled program. If you load the source file, rather than compiling it, body is evaluated normally.
Common Lisp Note: At top level, this is analogous to the Common Lisp idiom
(eval-when (compile eval) ...). Elsewhere, the Common Lisp ‘#.’ reader macro (but not when interpreting) is closer to whateval-when-compiledoes.
Byte-compiled functions have a special data type: they are byte-code function objects.
Internally, a byte-code function object is much like a vector; however, the evaluator handles this data type specially when it appears as a function to be called. The printed representation for a byte-code function object is like that for a vector, with an additional ‘#’ before the opening ‘[’.
A byte-code function object must have at least four elements; there is no maximum number, but only the first six elements have any normal use. They are:
nil. The value may
be a number or a list, in case the documentation string is stored in a
file. Use the function documentation to get the real
documentation string (see Accessing Documentation).
nil for a function that isn't interactive.
Here's an example of a byte-code function object, in printed
representation. It is the definition of the command
backward-sexp.
#[(&optional arg)
"^H\204^F^@\301^P\302^H[!\207"
[arg 1 forward-sexp]
2
254435
"p"]
The primitive way to create a byte-code object is with
make-byte-code:
This function constructs and returns a byte-code function object with elements as its elements.
You should not try to come up with the elements for a byte-code function yourself, because if they are inconsistent, Emacs may crash when you call the function. Always leave it to the byte compiler to create these objects; it makes the elements consistent (we hope).
You can access the elements of a byte-code object using aref;
you can also use vconcat to create a vector with the same
elements.
People do not write byte-code; that job is left to the byte compiler. But we provide a disassembler to satisfy a cat-like curiosity. The disassembler converts the byte-compiled code into humanly readable form.
The byte-code interpreter is implemented as a simple stack machine. It pushes values onto a stack of its own, then pops them off to use them in calculations whose results are themselves pushed back on the stack. When a byte-code function returns, it pops a value off the stack and returns it as the value of the function.
In addition to the stack, byte-code functions can use, bind, and set ordinary Lisp variables, by transferring values between variables and the stack.
This function prints the disassembled code for object. If stream is supplied, then output goes there. Otherwise, the disassembled code is printed to the stream
standard-output. The argument object can be a function name or a lambda expression.As a special exception, if this function is used interactively, it outputs to a buffer named ‘*Disassemble*’.
Here are two examples of using the disassemble function. We
have added explanatory comments to help you relate the byte-code to the
Lisp source; these do not appear in the output of disassemble.
These examples show unoptimized byte-code. Nowadays byte-code is
usually optimized, but we did not want to rewrite these examples, since
they still serve their purpose.
(defun factorial (integer)
"Compute factorial of an integer."
(if (= 1 integer) 1
(* integer (factorial (1- integer)))))
=> factorial
(factorial 4)
=> 24
(disassemble 'factorial)
-| byte-code for factorial:
doc: Compute factorial of an integer.
args: (integer)
0 constant 1 ; Push 1 onto stack.
1 varref integer ; Get value of integer
; from the environment
; and push the value
; onto the stack.
2 eqlsign ; Pop top two values off stack,
; compare them,
; and push result onto stack.
3 goto-if-nil 10 ; Pop and test top of stack;
; if nil, go to 10,
; else continue.
6 constant 1 ; Push 1 onto top of stack.
7 goto 17 ; Go to 17 (in this case, 1 will be
; returned by the function).
10 constant * ; Push symbol * onto stack.
11 varref integer ; Push value of integer onto stack.
12 constant factorial ; Push factorial onto stack.
13 varref integer ; Push value of integer onto stack.
14 sub1 ; Pop integer, decrement value,
; push new value onto stack.
; Stack now contains:
; − decremented value of integer
; − factorial
; − value of integer
; − *
15 call 1 ; Call function factorial using
; the first (i.e., the top) element
; of the stack as the argument;
; push returned value onto stack.
; Stack now contains:
; − result of recursive
; call to factorial
; − value of integer
; − *
16 call 2 ; Using the first two
; (i.e., the top two)
; elements of the stack
; as arguments,
; call the function *,
; pushing the result onto the stack.
17 return ; Return the top element
; of the stack.
=> nil
The silly-loop function is somewhat more complex:
(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
=> silly-loop
(disassemble 'silly-loop)
-| byte-code for silly-loop:
doc: Return time before and after N iterations of a loop.
args: (n)
0 constant current-time-string ; Push
; current-time-string
; onto top of stack.
1 call 0 ; Call current-time-string
; with no argument,
; pushing result onto stack.
2 varbind t1 ; Pop stack and bind t1
; to popped value.
3 varref n ; Get value of n from
; the environment and push
; the value onto the stack.
4 sub1 ; Subtract 1 from top of stack.
5 dup ; Duplicate the top of the stack;
; i.e., copy the top of
; the stack and push the
; copy onto the stack.
6 varset n ; Pop the top of the stack,
; and bind n to the value.
; In effect, the sequence dup varset
; copies the top of the stack
; into the value of n
; without popping it.
7 constant 0 ; Push 0 onto stack.
8 gtr ; Pop top two values off stack,
; test if n is greater than 0
; and push result onto stack.
9 goto-if-nil-else-pop 17 ; Goto 17 if n <= 0
; (this exits the while loop).
; else pop top of stack
; and continue
12 constant nil ; Push nil onto stack
; (this is the body of the loop).
13 discard ; Discard result of the body
; of the loop (a while loop
; is always evaluated for
; its side effects).
14 goto 3 ; Jump back to beginning
; of while loop.
17 discard ; Discard result of while loop
; by popping top of stack.
; This result is the value nil that
; was not popped by the goto at 9.
18 varref t1 ; Push value of t1 onto stack.
19 constant current-time-string ; Push
; current-time-string
; onto top of stack.
20 call 0 ; Call current-time-string again.
21 list2 ; Pop top two elements off stack,
; create a list of them,
; and push list onto stack.
22 unbind 1 ; Unbind t1 in local environment.
23 return ; Return value of the top of stack.
=> nil
The advice feature lets you add to the existing definition of a function, by advising the function. This is a clean method for a library to customize functions defined by other parts of Emacs—cleaner than redefining the whole function.
Each function can have multiple pieces of advice, separately defined. Each defined piece of advice can be enabled or disabled explicitly. All the enabled pieces of advice for any given function actually take effect when you activate advice for that function, or when you define or redefine the function. Note that enabling a piece of advice and activating advice for a function are not the same thing.
Usage Note: Advice is useful for altering the behavior of existing calls to an existing function. If you want the new behavior for new calls, or for key bindings, it is cleaner to define a new function (or a new command) which uses the existing function.
The command next-line moves point down vertically one or more
lines; it is the standard binding of C-n. When used on the last
line of the buffer, this command inserts a newline to create a line to
move to if next-line-add-newlines is non-nil (its default
is nil.)
Suppose you wanted to add a similar feature to previous-line,
which would insert a new line at the beginning of the buffer for the
command to move to. How could you do this?
You could do it by redefining the whole function, but that is not modular. The advice feature provides a cleaner alternative: you can effectively add your code to the existing function definition, without actually changing or even seeing that definition. Here is how to do this:
(defadvice previous-line (before next-line-at-end (arg))
"Insert an empty line when moving up from the top line."
(if (and next-line-add-newlines (= arg 1)
(save-excursion (beginning-of-line) (bobp)))
(progn
(beginning-of-line)
(newline))))
This expression defines a piece of advice for the function
previous-line. This piece of advice is named
next-line-at-end, and the symbol before says that it is
before-advice which should run before the regular definition of
previous-line. (arg) specifies how the advice code can
refer to the function's arguments.
When this piece of advice runs, it creates an additional line, in the situation where that is appropriate, but does not move point to that line. This is the correct way to write the advice, because the normal definition will run afterward and will move back to the newly inserted line.
Defining the advice doesn't immediately change the function
previous-line. That happens when you activate the advice,
like this:
(ad-activate 'previous-line)
This is what actually begins to use the advice that has been defined so
far for the function previous-line. Henceforth, whenever that
function is run, whether invoked by the user with C-p or
M-x, or called from Lisp, it runs the advice first, and its
regular definition second.
This example illustrates before-advice, which is one class of advice: it runs before the function's base definition. There are two other advice classes: after-advice, which runs after the base definition, and around-advice, which lets you specify an expression to wrap around the invocation of the base definition.
To define a piece of advice, use the macro defadvice. A call
to defadvice has the following syntax, which is based on the
syntax of defun and defmacro, but adds more:
(defadvice function (class name
[position] [arglist]
flags...)
[documentation-string]
[interactive-form]
body-forms...)
Here, function is the name of the function (or macro or special form) to be advised. From now on, we will write just “function” when describing the entity being advised, but this always includes macros and special forms.
class specifies the class of the advice—one of before,
after, or around. Before-advice runs before the function
itself; after-advice runs after the function itself; around-advice is
wrapped around the execution of the function itself. After-advice and
around-advice can override the return value by setting
ad-return-value.
While advice is executing, after the function's original definition has been executed, this variable holds its return value, which will ultimately be returned to the caller after finishing all the advice. After-advice and around-advice can arrange to return some other value by storing it in this variable.
The argument name is the name of the advice, a non-nil
symbol. The advice name uniquely identifies one piece of advice, within all
the pieces of advice in a particular class for a particular
function. The name allows you to refer to the piece of
advice—to redefine it, or to enable or disable it.
In place of the argument list in an ordinary definition, an advice definition calls for several different pieces of information.
The optional position specifies where, in the current list of
advice of the specified class, this new advice should be placed.
It should be either first, last or a number that specifies
a zero-based position (first is equivalent to 0). If no position
is specified, the default is first. Position values outside the
range of existing positions in this class are mapped to the beginning or
the end of the range, whichever is closer. The position value is
ignored when redefining an existing piece of advice.
The optional arglist can be used to define the argument list for the sake of advice. This becomes the argument list of the combined definition that is generated in order to run the advice (see Combined Definition). Therefore, the advice expressions can use the argument variables in this list to access argument values.
The argument list used in advice need not be the same as the argument list used in the original function, but must be compatible with it, so that it can handle the ways the function is actually called. If two pieces of advice for a function both specify an argument list, they must specify the same argument list.
See Argument Access in Advice, for more information about argument lists and advice, and a more flexible way for advice to access the arguments.
The remaining elements, flags, are symbols that specify further information about how to use this piece of advice. Here are the valid symbols and their meanings:
activateThis flag has no immediate effect if function itself is not defined yet (a
situation known as forward advice), because it is impossible to
activate an undefined function's advice. However, defining
function will automatically activate its advice.
protectunwind-protect form, so that it will execute even if the
previous code gets an error or uses throw. See Cleanups.
compileactivate is also specified.
See Combined Definition.
disablepreactivatedefadvice is
compiled or macroexpanded. This generates a compiled advised definition
according to the current advice state, which will be used during
activation if appropriate. See Preactivation.
This is useful only if this defadvice is byte-compiled.
The optional documentation-string serves to document this piece of
advice. When advice is active for function, the documentation for
function (as returned by documentation) combines the
documentation strings of all the advice for function with the
documentation string of its original function definition.
The optional interactive-form form can be supplied to change the interactive behavior of the original function. If more than one piece of advice has an interactive-form, then the first one (the one with the smallest position) found among all the advice takes precedence.
The possibly empty list of body-forms specifies the body of the advice. The body of an advice can access or change the arguments, the return value, the binding environment, and perform any other kind of side effect.
Warning: When you advise a macro, keep in mind that macros are expanded when a program is compiled, not when a compiled program is run. All subroutines used by the advice need to be available when the byte compiler expands the macro.
Around-advice lets you “wrap” a Lisp expression “around” the
original function definition. You specify where the original function
definition should go by means of the special symbol ad-do-it.
Where this symbol occurs inside the around-advice body, it is replaced
with a progn containing the forms of the surrounded code. Here
is an example:
(defadvice foo (around foo-around)
"Ignore case in `foo'."
(let ((case-fold-search t))
ad-do-it))
Its effect is to make sure that case is ignored in
searches when the original definition of foo is run.
This is not really a variable, but it is somewhat used like one in around-advice. It specifies the place to run the function's original definition and other “earlier” around-advice.
If the around-advice does not use ad-do-it, then it does not run
the original function definition. This provides a way to override the
original definition completely. (It also overrides lower-positioned
pieces of around-advice).
If the around-advice uses ad-do-it more than once, the original
definition is run at each place. In this way, around-advice can execute
the original definition (and lower-positioned pieces of around-advice)
several times. Another way to do that is by using ad-do-it
inside of a loop.
The macro defadvice resembles defun in that the code for
the advice, and all other information about it, are explicitly stated in
the source code. You can also create advice whose details are computed,
using the function ad-add-advice.
Calling
ad-add-adviceadds advice as a piece of advice to function in class class. The argument advice has this form:(name protected enabled definition)Here protected and enabled are flags, and definition is the expression that says what the advice should do. If enabled is
nil, this piece of advice is initially disabled (see Enabling Advice).If function already has one or more pieces of advice in the specified class, then position specifies where in the list to put the new piece of advice. The value of position can either be
first,last, or a number (counting from 0 at the beginning of the list). Numbers outside the range are mapped to the beginning or the end of the range, whichever is closer. The position value is ignored when redefining an existing piece of advice.If function already has a piece of advice with the same name, then the position argument is ignored and the old advice is replaced with the new one.
By default, advice does not take effect when you define it—only when
you activate advice for the function that was advised. You can
request the activation of advice for a function when you define the
advice, by specifying the activate flag in the defadvice.
But normally you activate the advice for a function by calling the
function ad-activate or one of the other activation commands
listed below.
Separating the activation of advice from the act of defining it permits you to add several pieces of advice to one function efficiently, without redefining the function over and over as each advice is added. More importantly, it permits defining advice for a function before that function is actually defined.
When a function's advice is first activated, the function's original definition is saved, and all enabled pieces of advice for that function are combined with the original definition to make a new definition. (Pieces of advice that are currently disabled are not used; see Enabling Advice.) This definition is installed, and optionally byte-compiled as well, depending on conditions described below.
In all of the commands to activate advice, if compile is t,
the command also compiles the combined definition which implements the
advice.
This command activates all the advice defined for function.
To activate advice for a function whose advice is already active is not a no-op. It is a useful operation which puts into effect any changes in that function's advice since the previous activation of advice for that function.
This command activates the advice for function if its advice is already activated. This is useful if you change the advice.
This command activates the advice for all functions whose advice is already activated. This is useful if you change the advice of some functions.
This command activates all pieces of advice whose names match regexp. More precisely, it activates all advice for any function which has at least one piece of advice that matches regexp.
This command deactivates all pieces of advice whose names match regexp. More precisely, it deactivates all advice for any function which has at least one piece of advice that matches regexp.
This command activates pieces of advice whose names match regexp, but only those for functions whose advice is already activated. Reactivating a function's advice is useful for putting into effect all the changes that have been made in its advice (including enabling and disabling specific pieces of advice; see Enabling Advice) since the last time it was activated.
Turn on automatic advice activation when a function is defined or redefined. If you turn on this mode, then advice takes effect immediately when defined.
Turn off automatic advice activation when a function is defined or redefined.
This variable controls whether to compile the combined definition that results from activating advice for a function.
A value of
alwaysspecifies to compile unconditionally. A value ofnilspecifies never compile the advice.A value of
maybespecifies to compile if the byte-compiler is already loaded. A value oflike-originalspecifies to compile the advice if the original definition of the advised function is compiled or a built-in function.This variable takes effect only if the compile argument of
ad-activate(or any of the above functions) was supplied asnil. If that argument is non-nil, that means to compile the advice regardless.
If the advised definition was constructed during “preactivation”
(see Preactivation), then that definition must already be compiled,
because it was constructed during byte-compilation of the file that
contained the defadvice with the preactivate flag.
Each piece of advice has a flag that says whether it is enabled or
not. By enabling or disabling a piece of advice, you can turn it on
and off without having to undefine and redefine it. For example, here is
how to disable a particular piece of advice named my-advice for
the function foo:
(ad-disable-advice 'foo 'before 'my-advice)
This function by itself only changes the enable flag for a piece of
advice. To make the change take effect in the advised definition, you
must activate the advice for foo again:
(ad-activate 'foo)
This command disables the piece of advice named name in class class on function.
This command enables the piece of advice named name in class class on function.
You can also disable many pieces of advice at once, for various functions, using a regular expression. As always, the changes take real effect only when you next reactivate advice for the functions in question.
This command disables all pieces of advice whose names match regexp, in all classes, on all functions.
This command enables all pieces of advice whose names match regexp, in all classes, on all functions.
Constructing a combined definition to execute advice is moderately expensive. When a library advises many functions, this can make loading the library slow. In that case, you can use preactivation to construct suitable combined definitions in advance.
To use preactivation, specify the preactivate flag when you
define the advice with defadvice. This defadvice call
creates a combined definition which embodies this piece of advice
(whether enabled or not) plus any other currently enabled advice for the
same function, and the function's own definition. If the
defadvice is compiled, that compiles the combined definition
also.
When the function's advice is subsequently activated, if the enabled advice for the function matches what was used to make this combined definition, then the existing combined definition is used, thus avoiding the need to construct one. Thus, preactivation never causes wrong results—but it may fail to do any good, if the enabled advice at the time of activation doesn't match what was used for preactivation.
Here are some symptoms that can indicate that a preactivation did not work properly, because of a mismatch.
byte-compile is included in the value of features even
though you did not ever explicitly use the byte-compiler.
Compiled preactivated advice works properly even if the function itself is not defined until later; however, the function needs to be defined when you compile the preactivated advice.
There is no elegant way to find out why preactivated advice is not being
used. What you can do is to trace the function
ad-cache-id-verification-code (with the function
trace-function-background) before the advised function's advice
is activated. After activation, check the value returned by
ad-cache-id-verification-code for that function: verified
means that the preactivated advice was used, while other values give
some information about why they were considered inappropriate.
Warning: There is one known case that can make preactivation fail, in that a preconstructed combined definition is used even though it fails to match the current state of advice. This can happen when two packages define different pieces of advice with the same name, in the same class, for the same function. But you should avoid that anyway.
The simplest way to access the arguments of an advised function in the body of a piece of advice is to use the same names that the function definition uses. To do this, you need to know the names of the argument variables of the original function.
While this simple method is sufficient in many cases, it has a disadvantage: it is not robust, because it hard-codes the argument names into the advice. If the definition of the original function changes, the advice might break.
Another method is to specify an argument list in the advice itself. This avoids the need to know the original function definition's argument names, but it has a limitation: all the advice on any particular function must use the same argument list, because the argument list actually used for all the advice comes from the first piece of advice for that function.
A more robust method is to use macros that are translated into the proper access forms at activation time, i.e., when constructing the advised definition. Access macros access actual arguments by position regardless of how these actual arguments get distributed onto the argument variables of a function. This is robust because in Emacs Lisp the meaning of an argument is strictly determined by its position in the argument list.
This returns the list of actual arguments supplied starting at position.
This sets the list of actual arguments starting at position to value-list.
Now an example. Suppose the function foo is defined as
(defun foo (x y &optional z &rest r) ...)
and is then called with
(foo 0 1 2 3 4 5 6)
which means that x is 0, y is 1, z is 2 and r is
(3 4 5 6) within the body of foo. Here is what
ad-get-arg and ad-get-args return in this case:
(ad-get-arg 0) => 0
(ad-get-arg 1) => 1
(ad-get-arg 2) => 2
(ad-get-arg 3) => 3
(ad-get-args 2) => (2 3 4 5 6)
(ad-get-args 4) => (4 5 6)
Setting arguments also makes sense in this example:
(ad-set-arg 5 "five")
has the effect of changing the sixth argument to "five". If this
happens in advice executed before the body of foo is run, then
r will be (3 4 "five" 6) within that body.
Here is an example of setting a tail of the argument list:
(ad-set-args 0 '(5 4 3 2 1 0))
If this happens in advice executed before the body of foo is run,
then within that body, x will be 5, y will be 4, z
will be 3, and r will be (2 1 0) inside the body of
foo.
These argument constructs are not really implemented as Lisp macros. Instead they are implemented specially by the advice mechanism.
When the advice facility constructs the combined definition, it needs
to know the argument list of the original function. This is not always
possible for primitive functions. When advice cannot determine the
argument list, it uses (&rest ad-subr-args), which always works
but is inefficient because it constructs a list of the argument values.
You can use ad-define-subr-args to declare the proper argument
names for a primitive function:
This function specifies that arglist should be used as the argument list for function function.
For example,
(ad-define-subr-args 'fset '(sym newdef))
specifies the argument list for the function fset.
Suppose that a function has n pieces of before-advice (numbered from 0 through n−1), m pieces of around-advice and k pieces of after-advice. Assuming no piece of advice is protected, the combined definition produced to implement the advice for a function looks like this:
(lambda arglist
[ [advised-docstring] [(interactive ...)] ]
(let (ad-return-value)
before-0-body-form...
....
before-n−1-body-form...
around-0-body-form...
around-1-body-form...
....
around-m−1-body-form...
(setq ad-return-value
apply original definition to arglist)
end-of-around-m−1-body-form...
....
end-of-around-1-body-form...
end-of-around-0-body-form...
after-0-body-form...
....
after-k−1-body-form...
ad-return-value))
Macros are redefined as macros, which means adding macro to
the beginning of the combined definition.
The interactive form is present if the original function or some piece
of advice specifies one. When an interactive primitive function is
advised, advice uses a special method: it calls the primitive with
call-interactively so that it will read its own arguments.
In this case, the advice cannot access the arguments.
The body forms of the various advice in each class are assembled according to their specified order. The forms of around-advice l are included in one of the forms of around-advice l − 1.
The innermost part of the around advice onion is
apply original definition to arglist
whose form depends on the type of the original function. The variable
ad-return-value is set to whatever this returns. The variable is
visible to all pieces of advice, which can access and modify it before
it is actually returned from the advised function.
The semantic structure of advised functions that contain protected
pieces of advice is the same. The only difference is that
unwind-protect forms ensure that the protected advice gets
executed even if some previous piece of advice had an error or a
non-local exit. If any around-advice is protected, then the whole
around-advice onion is protected as a result.
There are three ways to investigate a problem in an Emacs Lisp program, depending on what you are doing with the program when the problem appears.
Another useful debugging tool is the dribble file. When a dribble file is open, Emacs copies all keyboard input characters to that file. Afterward, you can examine the file to find out what input was used. See Terminal Input.
For debugging problems in terminal descriptions, the
open-termscript function can be useful. See Terminal Output.
The ordinary Lisp debugger provides the ability to suspend evaluation of a form. While evaluation is suspended (a state that is commonly known as a break), you may examine the run time stack, examine the values of local or global variables, or change those values. Since a break is a recursive edit, all the usual editing facilities of Emacs are available; you can even run programs that will enter the debugger recursively. See Recursive Editing.
The most important time to enter the debugger is when a Lisp error happens. This allows you to investigate the immediate causes of the error.
However, entry to the debugger is not a normal consequence of an
error. Many commands frequently cause Lisp errors when invoked
inappropriately (such as C-f at the end of the buffer), and during
ordinary editing it would be very inconvenient to enter the debugger
each time this happens. So if you want errors to enter the debugger, set
the variable debug-on-error to non-nil. (The command
toggle-debug-on-error provides an easy way to do this.)
This variable determines whether the debugger is called when an error is signaled and not handled. If
debug-on-errorist, all kinds of errors call the debugger (except those listed indebug-ignored-errors). If it isnil, none call the debugger.The value can also be a list of error conditions that should call the debugger. For example, if you set it to the list
(void-variable), then only errors about a variable that has no value invoke the debugger.When this variable is non-
nil, Emacs does not create an error handler around process filter functions and sentinels. Therefore, errors in these functions also invoke the debugger. See Processes.
This variable specifies certain kinds of errors that should not enter the debugger. Its value is a list of error condition symbols and/or regular expressions. If the error has any of those condition symbols, or if the error message matches any of the regular expressions, then that error does not enter the debugger, regardless of the value of
debug-on-error.The normal value of this variable lists several errors that happen often during editing but rarely result from bugs in Lisp programs. However, “rarely” is not “never”; if your program fails with an error that matches this list, you will need to change this list in order to debug the error. The easiest way is usually to set
debug-ignored-errorstonil.
Normally, errors that are caught by
condition-casenever run the debugger, even ifdebug-on-erroris non-nil. In other words,condition-casegets a chance to handle the error before the debugger gets a chance.If you set
debug-on-signalto a non-nilvalue, then the debugger gets the first chance at every error; an error will invoke the debugger regardless of anycondition-case, if it fits the criteria specified by the values ofdebug-on-erroranddebug-ignored-errors.Warning: This variable is strong medicine! Various parts of Emacs handle errors in the normal course of affairs, and you may not even realize that errors happen there. If you set
debug-on-signalto a non-nilvalue, those errors will enter the debugger.Warning:
debug-on-signalhas no effect whendebug-on-errorisnil.
To debug an error that happens during loading of the init
file, use the option ‘--debug-init’. This binds
debug-on-error to t while loading the init file, and
bypasses the condition-case which normally catches errors in the
init file.
If your init file sets debug-on-error, the effect may
not last past the end of loading the init file. (This is an undesirable
byproduct of the code that implements the ‘--debug-init’ command
line option.) The best way to make the init file set
debug-on-error permanently is with after-init-hook, like
this:
(add-hook 'after-init-hook
(lambda () (setq debug-on-error t)))
When a program loops infinitely and fails to return, your first problem is to stop the loop. On most operating systems, you can do this with C-g, which causes a quit.
Ordinary quitting gives no information about why the program was
looping. To get more information, you can set the variable
debug-on-quit to non-nil. Quitting with C-g is not
considered an error, and debug-on-error has no effect on the
handling of C-g. Likewise, debug-on-quit has no effect on
errors.
Once you have the debugger running in the middle of the infinite loop, you can proceed from the debugger using the stepping commands. If you step through the entire loop, you will probably get enough information to solve the problem.
This variable determines whether the debugger is called when
quitis signaled and not handled. Ifdebug-on-quitis non-nil, then the debugger is called whenever you quit (that is, type C-g). Ifdebug-on-quitisnil, then the debugger is not called when you quit. See Quitting.
To investigate a problem that happens in the middle of a program, one useful technique is to enter the debugger whenever a certain function is called. You can do this to the function in which the problem occurs, and then step through the function, or you can do this to a function called shortly before the problem, step quickly over the call to that function, and then step through its caller.
This function requests function-name to invoke the debugger each time it is called. It works by inserting the form
(debug 'debug)into the function definition as the first form.Any function defined as Lisp code may be set to break on entry, regardless of whether it is interpreted code or compiled code. If the function is a command, it will enter the debugger when called from Lisp and when called interactively (after the reading of the arguments). You can't debug primitive functions (i.e., those written in C) this way.
When
debug-on-entryis called interactively, it prompts for function-name in the minibuffer. If the function is already set up to invoke the debugger on entry,debug-on-entrydoes nothing.debug-on-entryalways returns function-name.Note: if you redefine a function after using
debug-on-entryon it, the code to enter the debugger is discarded by the redefinition. In effect, redefining the function cancels the break-on-entry feature for that function.(defun fact (n) (if (zerop n) 1 (* n (fact (1- n))))) => fact (debug-on-entry 'fact) => fact (fact 3) ------ Buffer: *Backtrace* ------ Entering: * fact(3) eval-region(4870 4878 t) byte-code("...") eval-last-sexp(nil) (let ...) eval-insert-last-sexp(nil) * call-interactively(eval-insert-last-sexp) ------ Buffer: *Backtrace* ------ (symbol-function 'fact) => (lambda (n) (debug (quote debug)) (if (zerop n) 1 (* n (fact (1- n)))))
This function undoes the effect of
debug-on-entryon function-name. When called interactively, it prompts for function-name in the minibuffer. If function-name isnilor the empty string, it cancels break-on-entry for all functions.Calling
cancel-debug-on-entrydoes nothing to a function which is not currently set up to break on entry. It always returns function-name.
You can cause the debugger to be called at a certain point in your
program by writing the expression (debug) at that point. To do
this, visit the source file, insert the text ‘(debug)’ at the
proper place, and type C-M-x. Warning: if you do this
for temporary debugging purposes, be sure to undo this insertion before
you save the file!
The place where you insert ‘(debug)’ must be a place where an
additional form can be evaluated and its value ignored. (If the value
of (debug) isn't ignored, it will alter the execution of the
program!) The most common suitable places are inside a progn or
an implicit progn (see Sequencing).
When the debugger is entered, it displays the previously selected buffer in one window and a buffer named ‘*Backtrace*’ in another window. The backtrace buffer contains one line for each level of Lisp function execution currently going on. At the beginning of this buffer is a message describing the reason that the debugger was invoked (such as the error message and associated data, if it was invoked due to an error).
The backtrace buffer is read-only and uses a special major mode, Debugger mode, in which letters are defined as debugger commands. The usual Emacs editing commands are available; thus, you can switch windows to examine the buffer that was being edited at the time of the error, switch buffers, visit files, or do any other sort of editing. However, the debugger is a recursive editing level (see Recursive Editing) and it is wise to go back to the backtrace buffer and exit the debugger (with the q command) when you are finished with it. Exiting the debugger gets out of the recursive edit and kills the backtrace buffer.
The backtrace buffer shows you the functions that are executing and their argument values. It also allows you to specify a stack frame by moving point to the line describing that frame. (A stack frame is the place where the Lisp interpreter records information about a particular invocation of a function.) The frame whose line point is on is considered the current frame. Some of the debugger commands operate on the current frame.
The debugger itself must be run byte-compiled, since it makes assumptions about how many stack frames are used for the debugger itself. These assumptions are false if the debugger is running interpreted.
Inside the debugger (in Debugger mode), these special commands are available in addition to the usual cursor motion commands. (Keep in mind that all the usual facilities of Emacs, such as switching windows or buffers, are still available.)
The most important use of debugger commands is for stepping through code, so that you can see how control flows. The debugger can step through the control structures of an interpreted function, but cannot do so in a byte-compiled function. If you would like to step through a byte-compiled function, replace it with an interpreted definition of the same function. (To do this, visit the source for the function and type C-M-x on its definition.)
Here is a list of Debugger mode commands:
Continuing is possible after entry to the debugger due to function entry
or exit, explicit invocation, or quitting. You cannot continue if the
debugger was entered because of an error.
The stack frame made for the function call which enters the debugger in
this way will be flagged automatically so that the debugger will be
called again when the frame is exited. You can use the u command
to cancel this flag.
If the debugger was entered due to a C-g but you really want
to quit, and not debug, use the q command.
The r command is useful when the debugger was invoked due to exit
from a Lisp call frame (as requested with b or by entering the
frame with d); then the value specified in the r command is
used as the value of that frame. It is also useful if you call
debug and use its return value. Otherwise, r has the same
effect as c, and the specified return value does not matter.
You can't use r when the debugger was entered due to an error.
Here we describe in full detail the function debug that is used
to invoke the debugger.
This function enters the debugger. It switches buffers to a buffer named ‘*Backtrace*’ (or ‘*Backtrace*<2>’ if it is the second recursive entry to the debugger, etc.), and fills it with information about the stack of Lisp function calls. It then enters a recursive edit, showing the backtrace buffer in Debugger mode.
The Debugger mode c and r commands exit the recursive edit; then
debugswitches back to the previous buffer and returns to whatever calleddebug. This is the only way the functiondebugcan return to its caller.The use of the debugger-args is that
debugdisplays the rest of its arguments at the top of the ‘*Backtrace*’ buffer, so that the user can see them. Except as described below, this is the only way these arguments are used.However, certain values for first argument to
debughave a special significance. (Normally, these values are used only by the internals of Emacs, and not by programmers callingdebug.) Here is a table of these special values:
lambda- A first argument of
lambdameansdebugwas called because of entry to a function whendebug-on-next-callwas non-nil. The debugger displays ‘Entering:’ as a line of text at the top of the buffer.debugdebugas first argument indicates a call todebugbecause of entry to a function that was set to debug on entry. The debugger displays ‘Entering:’, just as in thelambdacase. It also marks the stack frame for that function so that it will invoke the debugger when exited.t- When the first argument is
t, this indicates a call todebugdue to evaluation of a list form whendebug-on-next-callis non-nil. The debugger displays the following as the top line in the buffer:Beginning evaluation of function call form:exit- When the first argument is
exit, it indicates the exit of a stack frame previously marked to invoke the debugger on exit. The second argument given todebugin this case is the value being returned from the frame. The debugger displays ‘Return value:’ in the top line of the buffer, followed by the value being returned.error- When the first argument is
error, the debugger indicates that it is being entered because an error orquitwas signaled and not handled, by displaying ‘Signaling:’ followed by the error signaled and any arguments tosignal. For example,(let ((debug-on-error t)) (/ 1 0)) ------ Buffer: *Backtrace* ------ Signaling: (arith-error) /(1 0) ... ------ Buffer: *Backtrace* ------If an error was signaled, presumably the variable
debug-on-erroris non-nil. Ifquitwas signaled, then presumably the variabledebug-on-quitis non-nil.nil- Use
nilas the first of the debugger-args when you want to enter the debugger explicitly. The rest of the debugger-args are printed on the top line of the buffer. You can use this feature to display messages—for example, to remind yourself of the conditions under whichdebugis called.
This section describes functions and variables used internally by the debugger.
The value of this variable is the function to call to invoke the debugger. Its value must be a function of any number of arguments, or, more typically, the name of a function. This function should invoke some kind of debugger. The default value of the variable is
debug.The first argument that Lisp hands to the function indicates why it was called. The convention for arguments is detailed in the description of
debug.
This function prints a trace of Lisp function calls currently active. This is the function used by
debugto fill up the ‘*Backtrace*’ buffer. It is written in C, since it must have access to the stack to determine which function calls are active. The return value is alwaysnil.In the following example, a Lisp expression calls
backtraceexplicitly. This prints the backtrace to the streamstandard-output, which, in this case, is the buffer ‘backtrace-output’.Each line of the backtrace represents one function call. The line shows the values of the function's arguments if they are all known; if they are still being computed, the line says so. The arguments of special forms are elided.
(with-output-to-temp-buffer "backtrace-output" (let ((var 1)) (save-excursion (setq var (eval '(progn (1+ var) (list 'testing (backtrace)))))))) => nil ----------- Buffer: backtrace-output ------------ backtrace() (list ...computing arguments...) (progn ...) eval((progn (1+ var) (list (quote testing) (backtrace)))) (setq ...) (save-excursion ...) (let ...) (with-output-to-temp-buffer ...) eval-region(1973 2142 #<buffer *scratch*>) byte-code("... for eval-print-last-sexp ...") eval-print-last-sexp(nil) * call-interactively(eval-print-last-sexp) ----------- Buffer: backtrace-output ------------The character ‘*’ indicates a frame whose debug-on-exit flag is set.
If this variable is non-
nil, it says to call the debugger before the nexteval,applyorfuncall. Entering the debugger setsdebug-on-next-calltonil.The d command in the debugger works by setting this variable.
This function sets the debug-on-exit flag of the stack frame level levels down the stack, giving it the value flag. If flag is non-
nil, this will cause the debugger to be entered when that frame later exits. Even a nonlocal exit through that frame will enter the debugger.This function is used only by the debugger.
This variable records the debugging status of the current interactive command. Each time a command is called interactively, this variable is bound to
nil. The debugger can set this variable to leave information for future debugger invocations during the same command invocation.The advantage of using this variable rather than an ordinary global variable is that the data will never carry over to a subsequent command invocation.
The function
backtrace-frameis intended for use in Lisp debuggers. It returns information about what computation is happening in the stack frame frame-number levels down.If that frame has not evaluated the arguments yet, or is a special form, the value is
(nilfunction arg-forms...).If that frame has evaluated its arguments and called its function already, the return value is
(tfunction arg-values...).In the return value, function is whatever was supplied as the car of the evaluated list, or a
lambdaexpression in the case of a macro call. If the function has a&restargument, that is represented as the tail of the list arg-values.If frame-number is out of range,
backtrace-framereturnsnil.
Edebug is a source-level debugger for Emacs Lisp programs with which you can:
The first three sections below should tell you enough about Edebug to enable you to use it.
To debug a Lisp program with Edebug, you must first instrument
the Lisp code that you want to debug. A simple way to do this is to
first move point into the definition of a function or macro and then do
C-u C-M-x (eval-defun with a prefix argument). See
Instrumenting, for alternative ways to instrument code.
Once a function is instrumented, any call to the function activates Edebug. Depending on which Edebug execution mode you have selected, activating Edebug may stop execution and let you step through the function, or it may update the display and continue execution while checking for debugging commands. The default execution mode is step, which stops execution. See Edebug Execution Modes.
Within Edebug, you normally view an Emacs buffer showing the source of the Lisp code you are debugging. This is referred to as the source code buffer, and it is temporarily read-only.
An arrow at the left margin indicates the line where the function is executing. Point initially shows where within the line the function is executing, but this ceases to be true if you move point yourself.
If you instrument the definition of fac (shown below) and then
execute (fac 3), here is what you would normally see. Point is
at the open-parenthesis before if.
(defun fac (n)
=>-!-(if (< 0 n)
(* n (fac (1- n)))
1))
The places within a function where Edebug can stop execution are called
stop points. These occur both before and after each subexpression
that is a list, and also after each variable reference.
Here we use periods to show the stop points in the function
fac:
(defun fac (n)
.(if .(< 0 n.).
.(* n. .(fac (1- n.).).).
1).)
The special commands of Edebug are available in the source code buffer
in addition to the commands of Emacs Lisp mode. For example, you can
type the Edebug command <SPC> to execute until the next stop point.
If you type <SPC> once after entry to fac, here is the
display you will see:
(defun fac (n)
=>(if -!-(< 0 n)
(* n (fac (1- n)))
1))
When Edebug stops execution after an expression, it displays the expression's value in the echo area.
Other frequently used commands are b to set a breakpoint at a stop point, g to execute until a breakpoint is reached, and q to exit Edebug and return to the top-level command loop. Type ? to display a list of all Edebug commands.
In order to use Edebug to debug Lisp code, you must first instrument the code. Instrumenting code inserts additional code into it, to invoke Edebug at the proper places.
Once you have loaded Edebug, the command C-M-x
(eval-defun) is redefined so that when invoked with a prefix
argument on a definition, it instruments the definition before
evaluating it. (The source code itself is not modified.) If the
variable edebug-all-defs is non-nil, that inverts the
meaning of the prefix argument: in this case, C-M-x instruments the
definition unless it has a prefix argument. The default value of
edebug-all-defs is nil. The command M-x
edebug-all-defs toggles the value of the variable
edebug-all-defs.
If edebug-all-defs is non-nil, then the commands
eval-region, eval-current-buffer, and eval-buffer
also instrument any definitions they evaluate. Similarly,
edebug-all-forms controls whether eval-region should
instrument any form, even non-defining forms. This doesn't apply
to loading or evaluations in the minibuffer. The command M-x
edebug-all-forms toggles this option.
Another command, M-x edebug-eval-top-level-form, is available to
instrument any top-level form regardless of the values of
edebug-all-defs and edebug-all-forms.
While Edebug is active, the command I
(edebug-instrument-callee) instruments the definition of the
function or macro called by the list form after point, if is not already
instrumented. This is possible only if Edebug knows where to find the
source for that function; for this reading, after loading Edebug,
eval-region records the position of every definition it
evaluates, even if not instrumenting it. See also the i command
(see Jumping), which steps into the call after instrumenting the
function.
Edebug knows how to instrument all the standard special forms,
interactive forms with an expression argument, anonymous lambda
expressions, and other defining forms. However, Edebug cannot determine
on its own what a user-defined macro will do with the arguments of a
macro call, so you must provide that information; see Instrumenting Macro Calls, for details.
When Edebug is about to instrument code for the first time in a
session, it runs the hook edebug-setup-hook, then sets it to
nil. You can use this to load Edebug specifications
(see Instrumenting Macro Calls) associated with a package you are
using, but only when you use Edebug.
To remove instrumentation from a definition, simply re-evaluate its
definition in a way that does not instrument. There are two ways of
evaluating forms that never instrument them: from a file with
load, and from the minibuffer with eval-expression
(M-:).
If Edebug detects a syntax error while instrumenting, it leaves point
at the erroneous code and signals an invalid-read-syntax error.
See Edebug Eval, for other evaluation functions available inside of Edebug.
Edebug supports several execution modes for running the program you are debugging. We call these alternatives Edebug execution modes; do not confuse them with major or minor modes. The current Edebug execution mode determines how far Edebug continues execution before stopping—whether it stops at each stop point, or continues to the next breakpoint, for example—and how much Edebug displays the progress of the evaluation before it stops.
Normally, you specify the Edebug execution mode by typing a command to continue the program in a certain mode. Here is a table of these commands; all except for S resume execution of the program, at least for a certain distance.
edebug-stop).
edebug-step-mode).
edebug-next-mode). Also see edebug-forward-sexp in
Edebug Misc.
edebug-trace-mode).
edebug-Trace-fast-mode).
edebug-go-mode). See Breakpoints.
edebug-continue-mode).
edebug-Continue-fast-mode).
edebug-Go-nonstop-mode). You
can still stop the program by typing S, or any editing command.
In general, the execution modes earlier in the above list run the program more slowly or stop sooner than the modes later in the list.
While executing or tracing, you can interrupt the execution by typing any Edebug command. Edebug stops the program at the next stop point and then executes the command you typed. For example, typing t during execution switches to trace mode at the next stop point. You can use S to stop execution without doing anything else.
If your function happens to read input, a character you type intending to interrupt execution may be read by the function instead. You can avoid such unintended results by paying attention to when your program wants input.
Keyboard macros containing the commands in this section do not
completely work: exiting from Edebug, to resume the program, loses track
of the keyboard macro. This is not easy to fix. Also, defining or
executing a keyboard macro outside of Edebug does not affect commands
inside Edebug. This is usually an advantage. See also the
edebug-continue-kbd-macro option (see Edebug Options).
When you enter a new Edebug level, the initial execution mode comes from
the value of the variable edebug-initial-mode. By default, this
specifies step mode. Note that you may reenter the same Edebug level
several times if, for example, an instrumented function is called
several times from one command.
The commands described in this section execute until they reach a specified location. All except i make a temporary breakpoint to establish the place to stop, then switch to go mode. Any other breakpoint reached before the intended stop point will also stop execution. See Breakpoints, for the details on breakpoints.
These commands may fail to work as expected in case of nonlocal exit, as that can bypass the temporary breakpoint where you expected the program to stop.
edebug-goto-here).
edebug-forward-sexp).
The h command proceeds to the stop point near the current location of point, using a temporary breakpoint. See Breakpoints, for more information about breakpoints.
The f command runs the program forward over one expression. More precisely, it sets a temporary breakpoint at the position that C-M-f would reach, then executes in go mode so that the program will stop at breakpoints.
With a prefix argument n, the temporary breakpoint is placed n sexps beyond point. If the containing list ends before n more elements, then the place to stop is after the containing expression.
You must check that the position C-M-f finds is a place that the
program will really get to. In cond, for example, this may not
be true.
For flexibility, the f command does forward-sexp starting
at point, rather than at the stop point. If you want to execute one
expression from the current stop point, first type w, to
move point there, and then type f.
The o command continues “out of” an expression. It places a temporary breakpoint at the end of the sexp containing point. If the containing sexp is a function definition itself, o continues until just before the last sexp in the definition. If that is where you are now, it returns from the function and then stops. In other words, this command does not exit the currently executing function unless you are positioned after the last sexp.
The i command steps into the function or macro called by the list form after point, and stops at its first stop point. Note that the form need not be the one about to be evaluated. But if the form is a function call about to be evaluated, remember to use this command before any of the arguments are evaluated, since otherwise it will be too late.
The i command instruments the function or macro it's supposed to step into, if it isn't instrumented already. This is convenient, but keep in mind that the function or macro remains instrumented unless you explicitly arrange to deinstrument it.
Some miscellaneous Edebug commands are described here.
edebug-help).
abort-recursive-edit).
top-level). This
exits all recursive editing levels, including all levels of Edebug
activity. However, instrumented code protected with
unwind-protect or condition-case forms may resume
debugging.
top-level-nonstop).
edebug-previous-result).
edebug-backtrace).
You cannot use debugger commands in the backtrace buffer in Edebug as you would in the standard debugger.
The backtrace buffer is killed automatically when you continue execution.
You can invoke commands from Edebug that activate Edebug again recursively. Whenever Edebug is active, you can quit to the top level with q or abort one recursive edit level with C-]. You can display a backtrace of all the pending evaluations with d.
Edebug's step mode stops execution when the next stop point is reached. There are three other ways to stop Edebug execution once it has started: breakpoints, the global break condition, and source breakpoints.
While using Edebug, you can specify breakpoints in the program you are testing: these are places where execution should stop. You can set a breakpoint at any stop point, as defined in Using Edebug. For setting and unsetting breakpoints, the stop point that is affected is the first one at or after point in the source code buffer. Here are the Edebug commands for breakpoints:
edebug-set-breakpoint). If you use a prefix argument, the
breakpoint is temporary—it turns off the first time it stops the
program.
edebug-unset-breakpoint).
nil value
(edebug-set-conditional-breakpoint). With a prefix argument, the
breakpoint is temporary.
edebug-next-breakpoint).
While in Edebug, you can set a breakpoint with b and unset one with u. First move point to the Edebug stop point of your choice, then type b or u to set or unset a breakpoint there. Unsetting a breakpoint where none has been set has no effect.
Re-evaluating or reinstrumenting a definition removes all of its previous breakpoints.
A conditional breakpoint tests a condition each time the program
gets there. Any errors that occur as a result of evaluating the
condition are ignored, as if the result were nil. To set a
conditional breakpoint, use x, and specify the condition
expression in the minibuffer. Setting a conditional breakpoint at a
stop point that has a previously established conditional breakpoint puts
the previous condition expression in the minibuffer so you can edit it.
You can make a conditional or unconditional breakpoint temporary by using a prefix argument with the command to set the breakpoint. When a temporary breakpoint stops the program, it is automatically unset.
Edebug always stops or pauses at a breakpoint, except when the Edebug mode is Go-nonstop. In that mode, it ignores breakpoints entirely.
To find out where your breakpoints are, use the B command, which moves point to the next breakpoint following point, within the same function, or to the first breakpoint if there are no following breakpoints. This command does not continue execution—it just moves point in the buffer.
A global break condition stops execution when a specified
condition is satisfied, no matter where that may occur. Edebug
evaluates the global break condition at every stop point; if it
evaluates to a non-nil value, then execution stops or pauses
depending on the execution mode, as if a breakpoint had been hit. If
evaluating the condition gets an error, execution does not stop.
The condition expression is stored in
edebug-global-break-condition. You can specify a new expression
using the X command (edebug-set-global-break-condition).
The global break condition is the simplest way to find where in your
code some event occurs, but it makes code run much more slowly. So you
should reset the condition to nil when not using it.
All breakpoints in a definition are forgotten each time you
reinstrument it. If you wish to make a breakpoint that won't be
forgotten, you can write a source breakpoint, which is simply a
call to the function edebug in your source code. You can, of
course, make such a call conditional. For example, in the fac
function, you can insert the first line as shown below, to stop when the
argument reaches zero:
(defun fac (n)
(if (= n 0) (edebug))
(if (< 0 n)
(* n (fac (1- n)))
1))
When the fac definition is instrumented and the function is
called, the call to edebug acts as a breakpoint. Depending on
the execution mode, Edebug stops or pauses there.
If no instrumented code is being executed when edebug is called,
that function calls debug.
Emacs normally displays an error message when an error is signaled and
not handled with condition-case. While Edebug is active and
executing instrumented code, it normally responds to all unhandled
errors. You can customize this with the options edebug-on-error
and edebug-on-quit; see Edebug Options.
When Edebug responds to an error, it shows the last stop point encountered before the error. This may be the location of a call to a function which was not instrumented, and within which the error actually occurred. For an unbound variable error, the last known stop point might be quite distant from the offending variable reference. In that case, you might want to display a full backtrace (see Edebug Misc).
If you change debug-on-error or debug-on-quit while
Edebug is active, these changes will be forgotten when Edebug becomes
inactive. Furthermore, during Edebug's recursive edit, these variables
are bound to the values they had outside of Edebug.
These Edebug commands let you view aspects of the buffer and window status as they were before entry to Edebug. The outside window configuration is the collection of windows and contents that were in effect outside of Edebug.
edebug-view-outside).
edebug-bounce-point). With a prefix argument n,
pause for n seconds instead.
edebug-where).
If you use this command in a different window displaying the same
buffer, that window will be used instead to display the current
definition in the future.
edebug-toggle-save-windows).
With a prefix argument, W only toggles saving and restoring of
the selected window. To specify a window that is not displaying the
source code buffer, you must use C-x X W from the global keymap.
You can view the outside window configuration with v or just bounce to the point in the current buffer with p, even if it is not normally displayed. After moving point, you may wish to jump back to the stop point with w from a source code buffer.
Each time you use W to turn saving off, Edebug forgets the saved outside window configuration—so that even if you turn saving back on, the current window configuration remains unchanged when you next exit Edebug (by continuing the program). However, the automatic redisplay of ‘*edebug*’ and ‘*edebug-trace*’ may conflict with the buffers you wish to see unless you have enough windows open.
While within Edebug, you can evaluate expressions “as if” Edebug were not running. Edebug tries to be invisible to the expression's evaluation and printing. Evaluation of expressions that cause side effects will work as expected, except for changes to data that Edebug explicitly saves and restores. See The Outside Context, for details on this process.
edebug-eval-expression). That is, Edebug tries to minimize its
interference with the evaluation.
edebug-eval-last-sexp).
Edebug supports evaluation of expressions containing references to
lexically bound symbols created by the following constructs in
cl.el (version 2.03 or later): lexical-let,
macrolet, and symbol-macrolet.
You can use the evaluation list buffer, called ‘*edebug*’, to evaluate expressions interactively. You can also set up the evaluation list of expressions to be evaluated automatically each time Edebug updates the display.
edebug-visit-eval-list).
In the ‘*edebug*’ buffer you can use the commands of Lisp Interaction mode (see Lisp Interaction) as well as these special commands:
edebug-eval-print-last-sexp).
edebug-eval-last-sexp).
edebug-update-eval-list).
edebug-delete-eval-item).
edebug-where).
You can evaluate expressions in the evaluation list window with C-j or C-x C-e, just as you would in ‘*scratch*’; but they are evaluated in the context outside of Edebug.
The expressions you enter interactively (and their results) are lost when you continue execution; but you can set up an evaluation list consisting of expressions to be evaluated each time execution stops.
To do this, write one or more evaluation list groups in the evaluation list buffer. An evaluation list group consists of one or more Lisp expressions. Groups are separated by comment lines.
The command C-c C-u (edebug-update-eval-list) rebuilds the
evaluation list, scanning the buffer and using the first expression of
each group. (The idea is that the second expression of the group is the
value previously computed and displayed.)
Each entry to Edebug redisplays the evaluation list by inserting each expression in the buffer, followed by its current value. It also inserts comment lines so that each expression becomes its own group. Thus, if you type C-c C-u again without changing the buffer text, the evaluation list is effectively unchanged.
If an error occurs during an evaluation from the evaluation list, the error message is displayed in a string as if it were the result. Therefore, expressions that use variables not currently valid do not interrupt your debugging.
Here is an example of what the evaluation list window looks like after several expressions have been added to it:
(current-buffer)
#<buffer *scratch*>
;---------------------------------------------------------------
(selected-window)
#<window 16 on *scratch*>
;---------------------------------------------------------------
(point)
196
;---------------------------------------------------------------
bad-var
"Symbol's value as variable is void: bad-var"
;---------------------------------------------------------------
(recursion-depth)
0
;---------------------------------------------------------------
this-command
eval-last-sexp
;---------------------------------------------------------------
To delete a group, move point into it and type C-c C-d, or simply delete the text for the group and update the evaluation list with C-c C-u. To add a new expression to the evaluation list, insert the expression at a suitable place, insert a new comment line, then type C-c C-u. You need not insert dashes in the comment line—its contents don't matter.
After selecting ‘*edebug*’, you can return to the source code buffer with C-c C-w. The ‘*edebug*’ buffer is killed when you continue execution, and recreated next time it is needed.
If an expression in your program produces a value containing circular list structure, you may get an error when Edebug attempts to print it.
One way to cope with circular structure is to set print-length
or print-level to truncate the printing. Edebug does this for
you; it binds print-length and print-level to 50 if they
were nil. (Actually, the variables edebug-print-length
and edebug-print-level specify the values to use within Edebug.)
See Output Variables.
If non-
nil, Edebug bindsprint-lengthto this value while printing results. The default value is50.
If non-
nil, Edebug bindsprint-levelto this value while printing results. The default value is50.
You can also print circular structures and structures that share
elements more informatively by binding print-circle
to a non-nil value.
Here is an example of code that creates a circular structure:
(setq a '(x y))
(setcar a a)
Custom printing prints this as ‘Result: #1=(#1# y)’. The ‘#1=’ notation labels the structure that follows it with the label ‘1’, and the ‘#1#’ notation references the previously labeled structure. This notation is used for any shared elements of lists or vectors.
If non-
nil, Edebug bindsprint-circleto this value while printing results. The default value isnil.
Other programs can also use custom printing; see cust-print.el for details.
Edebug can record an execution trace, storing it in a buffer named
‘*edebug-trace*’. This is a log of function calls and returns,
showing the function names and their arguments and values. To enable
trace recording, set edebug-trace to a non-nil value.
Making a trace buffer is not the same thing as using trace execution mode (see Edebug Execution Modes).
When trace recording is enabled, each function entry and exit adds lines to the trace buffer. A function entry record consists of ‘::::{’, followed by the function name and argument values. A function exit record consists of ‘::::}’, followed by the function name and result of the function.
The number of ‘:’s in an entry shows its recursion depth. You can use the braces in the trace buffer to find the matching beginning or end of function calls.
You can customize trace recording for function entry and exit by
redefining the functions edebug-print-trace-before and
edebug-print-trace-after.
This macro requests additional trace information around the execution of the body forms. The argument string specifies text to put in the trace buffer. All the arguments are evaluated, and
edebug-tracingreturns the value of the last form in body.
This function inserts text in the trace buffer. It computes the text with
(apply 'formatformat-string format-args). It also appends a newline to separate entries.
edebug-tracing and edebug-trace insert lines in the
trace buffer whenever they are called, even if Edebug is not active.
Adding text to the trace buffer also scrolls its window to show the last
lines inserted.
Edebug provides rudimentary coverage testing and display of execution frequency.
Coverage testing works by comparing the result of each expression with the previous result; each form in the program is considered “covered” if it has returned two different values since you began testing coverage in the current Emacs session. Thus, to do coverage testing on your program, execute it under various conditions and note whether it behaves correctly; Edebug will tell you when you have tried enough different conditions that each form has returned two different values.
Coverage testing makes execution slower, so it is only done if
edebug-test-coverage is non-nil. Frequency counting is
performed for all execution of an instrumented function, even if the
execution mode is Go-nonstop, and regardless of whether coverage testing
is enabled.
Use M-x edebug-display-freq-count to display both the coverage information and the frequency counts for a definition.
This command displays the frequency count data for each line of the current definition.
The frequency counts appear as comment lines after each line of code, and you can undo all insertions with one
undocommand. The counts appear under the ‘(’ before an expression or the ‘)’ after an expression, or on the last character of a variable. To simplify the display, a count is not shown if it is equal to the count of an earlier expression on the same line.The character ‘=’ following the count for an expression says that the expression has returned the same value each time it was evaluated. In other words, it is not yet “covered” for coverage testing purposes.
To clear the frequency count and coverage data for a definition, simply reinstrument it with
eval-defun.
For example, after evaluating (fac 5) with a source
breakpoint, and setting edebug-test-coverage to t, when
the breakpoint is reached, the frequency data looks like this:
(defun fac (n)
(if (= n 0) (edebug))
;#6 1 0 =5
(if (< 0 n)
;#5 =
(* n (fac (1- n)))
;# 5 0
1))
;# 0
The comment lines show that fac was called 6 times. The
first if statement returned 5 times with the same result each
time; the same is true of the condition on the second if.
The recursive call of fac did not return at all.
Edebug tries to be transparent to the program you are debugging, but it does not succeed completely. Edebug also tries to be transparent when you evaluate expressions with e or with the evaluation list buffer, by temporarily restoring the outside context. This section explains precisely what context Edebug restores, and how Edebug fails to be completely transparent.
Whenever Edebug is entered, it needs to save and restore certain data before even deciding whether to make trace information or stop the program.
max-lisp-eval-depth and max-specpdl-size are both
incremented once to reduce Edebug's impact on the stack. You could,
however, still run out of stack space when using Edebug.
executing-macro is bound to
edebug-continue-kbd-macro.
When Edebug needs to display something (e.g., in trace mode), it saves the current window configuration from “outside” Edebug (see Window Configurations). When you exit Edebug (by continuing the program), it restores the previous window configuration.
Emacs redisplays only when it pauses. Usually, when you continue execution, the program re-enters Edebug at a breakpoint or after stepping, without pausing or reading input in between. In such cases, Emacs never gets a chance to redisplay the “outside” configuration. Consequently, what you see is the same window configuration as the last time Edebug was active, with no interruption.
Entry to Edebug for displaying something also saves and restores the following data (though some of them are deliberately not restored if an error or quit signal occurs).
edebug-save-windows is non-nil (see Edebug Display Update).
The window configuration is not restored on error or quit, but the
outside selected window is reselected even on error or quit in
case a save-excursion is active. If the value of
edebug-save-windows is a list, only the listed windows are saved
and restored.
The window start and horizontal scrolling of the source code buffer are not restored, however, so that the display remains coherent within Edebug.
edebug-save-displayed-buffer-points is non-nil.
overlay-arrow-position and
overlay-arrow-string are saved and restored. So you can safely
invoke Edebug from the recursive edit elsewhere in the same buffer.
cursor-in-echo-area is locally bound to nil so that
the cursor shows up in the window.
When Edebug is entered and actually reads commands from the user, it saves (and later restores) these additional data:
last-command, this-command, last-command-char,
last-input-char, last-input-event,
last-command-event, last-event-frame,
last-nonmenu-event, and track-mouse. Commands used within
Edebug do not affect these variables outside of Edebug.
The key sequence returned by this-command-keys is changed by
executing commands within Edebug and there is no way to reset
the key sequence from Lisp.
Edebug cannot save and restore the value of
unread-command-events. Entering Edebug while this variable has a
nontrivial value can interfere with execution of the program you are
debugging.
command-history. In rare cases this can alter execution.
standard-output and standard-input are bound to nil
by the recursive-edit, but Edebug temporarily restores them during
evaluations.
defining-kbd-macro is bound to
edebug-continue-kbd-macro.
When Edebug instruments an expression that calls a Lisp macro, it needs additional information about the macro to do the job properly. This is because there is no a-priori way to tell which subexpressions of the macro call are forms to be evaluated. (Evaluation may occur explicitly in the macro body, or when the resulting expansion is evaluated, or any time later.)
Therefore, you must define an Edebug specification for each macro that
Edebug will encounter, to explain the format of calls to that macro. To
do this, use def-edebug-spec.
Specify which expressions of a call to macro macro are forms to be evaluated. For simple macros, the specification often looks very similar to the formal argument list of the macro definition, but specifications are much more general than macro arguments.
The macro argument can actually be any symbol, not just a macro name.
Here is a simple example that defines the specification for the
for example macro (see Argument Evaluation), followed by an
alternative, equivalent specification.
(def-edebug-spec for
(symbolp "from" form "to" form "do" &rest form))
(def-edebug-spec for
(symbolp ['from form] ['to form] ['do body]))
Here is a table of the possibilities for specification and how each directs processing of arguments.
t0A specification list is required for an Edebug specification if
some arguments of a macro call are evaluated while others are not. Some
elements in a specification list match one or more arguments, but others
modify the processing of all following elements. The latter, called
specification keywords, are symbols beginning with ‘&’ (such
as &optional).
A specification list may contain sublists which match arguments that are themselves lists, or it may contain vectors used for grouping. Sublists and groups thus subdivide the specification list into a hierarchy of levels. Specification keywords apply only to the remainder of the sublist or group they are contained in.
When a specification list involves alternatives or repetition, matching it against an actual macro call may require backtracking. See Backtracking, for more details.
Edebug specifications provide the power of regular expression matching, plus some context-free grammar constructs: the matching of sublists with balanced parentheses, recursive processing of forms, and recursion via indirect specifications.
Here's a table of the possible elements of a specification list, with their meanings:
sexpformplacesetf construct.
body&rest form. See &rest below.
function-formquote rather than
function, since it instruments the body of the lambda expression
either way.
lambda-expr&optionalTo make just a few elements optional followed by non-optional elements,
use [&optional specs...]. To specify that several
elements must all match or none, use &optional
[specs...]. See the defun example below.
&restTo repeat only a few elements, use [&rest specs...].
To specify several elements that must all match on every repetition, use
&rest [specs...].
&or&or
specification fails.
Each list element following &or is a single alternative. To
group two or more list elements as a single alternative, enclose them in
[...].
¬&or, but if any of them match, the specification fails. If none
of them match, nothing is matched, but the ¬ specification
succeeds.
&define&define keyword should be the first element in
a list specification.
nilgatelet example
below.
If the symbol has an Edebug specification, this indirect
specification should be either a list specification that is used in
place of the symbol, or a function that is called to process the
arguments. The specification may be defined with def-edebug-spec
just as for macros. See the defun example below.
Otherwise, the symbol should be a predicate. The predicate is called
with the argument and the specification fails if the predicate returns
nil. In either case, that argument is not instrumented.
Some suitable predicates include symbolp, integerp,
stringp, vectorp, and atom.
[elements...]"string"'symbol, where the name
of symbol is the string, but the string form is preferred.
(vector elements...)(elements...)A sublist specification may be a dotted list and the corresponding list
argument may then be a dotted list. Alternatively, the last cdr of a
dotted list specification may be another sublist specification (via a
grouping or an indirect specification, e.g., (spec . [(more
specs...)])) whose elements match the non-dotted list arguments.
This is useful in recursive specifications such as in the backquote
example below. Also see the description of a nil specification
above for terminating such recursion.
Note that a sublist specification written as (specs . nil)
is equivalent to (specs), and (specs .
(sublist-elements...)) is equivalent to (specs
sublist-elements...).
Here is a list of additional specifications that may appear only after
&define. See the defun example below.
nameA defining form is not required to have a name field; and it may have
multiple name fields.
:name:name should be a symbol; it is used as an additional
name component for the definition. You can use this to add a unique,
static component to the name of the definition. It may be used more
than once.
arglambda-listdef-bodybody, described above, but a definition body must be instrumented
with a different Edebug call that looks up information associated with
the definition. Use def-body for the highest level list of forms
within the definition.
def-formdef-body, except use this to match a single form rather than
a list of forms. As a special case, def-form also means that
tracing information is not output when the form is executed. See the
interactive example below.
If a specification fails to match at some point, this does not necessarily mean a syntax error will be signaled; instead, backtracking will take place until all alternatives have been exhausted. Eventually every element of the argument list must be matched by some element in the specification, and every required element in the specification must match some argument.
When a syntax error is detected, it might not be reported until much
later after higher-level alternatives have been exhausted, and with the
point positioned further from the real error. But if backtracking is
disabled when an error occurs, it can be reported immediately. Note
that backtracking is also reenabled automatically in several situations;
it is reenabled when a new alternative is established by
&optional, &rest, or &or, or at the start of
processing a sublist, group, or indirect specification. The effect of
enabling or disabling backtracking is limited to the remainder of the
level currently being processed and lower levels.
Backtracking is disabled while matching any of the
form specifications (that is, form, body, def-form, and
def-body). These specifications will match any form so any error
must be in the form itself rather than at a higher level.
Backtracking is also disabled after successfully matching a quoted
symbol or string specification, since this usually indicates a
recognized construct. But if you have a set of alternative constructs that
all begin with the same symbol, you can usually work around this
constraint by factoring the symbol out of the alternatives, e.g.,
["foo" &or [first case] [second case] ...].
Most needs are satisfied by these two ways that bactracking is
automatically disabled, but occasionally it is useful to explicitly
disable backtracking by using the gate specification. This is
useful when you know that no higher alternatives could apply. See the
example of the let specification.
It may be easier to understand Edebug specifications by studying the examples provided here.
A let special form has a sequence of bindings and a body. Each
of the bindings is either a symbol or a sublist with a symbol and
optional expression. In the specification below, notice the gate
inside of the sublist to prevent backtracking once a sublist is found.
(def-edebug-spec let
((&rest
&or symbolp (gate symbolp &optional form))
body))
Edebug uses the following specifications for defun and
defmacro and the associated argument list and interactive
specifications. It is necessary to handle interactive forms specially
since an expression argument it is actually evaluated outside of the
function body.
(def-edebug-spec defmacro defun) ; Indirect ref todefunspec. (def-edebug-spec defun (&define name lambda-list [&optional stringp] ; Match the doc string, if present. [&optional ("interactive" interactive)] def-body)) (def-edebug-spec lambda-list (([&rest arg] [&optional ["&optional" arg &rest arg]] &optional ["&rest" arg] ))) (def-edebug-spec interactive (&optional &or stringp def-form)) ; Notice:def-form
The specification for backquote below illustrates how to match
dotted lists and use nil to terminate recursion. It also
illustrates how components of a vector may be matched. (The actual
specification defined by Edebug does not support dotted lists because
doing so causes very deep recursion that could fail.)
(def-edebug-spec ` (backquote-form)) ; Alias just for clarity.
(def-edebug-spec backquote-form
(&or ([&or "," ",@"] &or ("quote" backquote-form) form)
(backquote-form . [&or nil backquote-form])
(vector &rest backquote-form)
sexp))
These options affect the behavior of Edebug:
Functions to call before Edebug is used. Each time it is set to a new value, Edebug will call those functions once and then
edebug-setup-hookis reset tonil. You could use this to load up Edebug specifications associated with a package you are using but only when you also use Edebug. See Instrumenting.
If this is non-
nil, normal evaluation of defining forms such asdefunanddefmacroinstruments them for Edebug. This applies toeval-defun,eval-region,eval-buffer, andeval-current-buffer.Use the command M-x edebug-all-defs to toggle the value of this option. See Instrumenting.
If this is non-
nil, the commandseval-defun,eval-region,eval-buffer, andeval-current-bufferinstrument all forms, even those that don't define anything. This doesn't apply to loading or evaluations in the minibuffer.Use the command M-x edebug-all-forms to toggle the value of this option. See Instrumenting.
If this is non-
nil, Edebug saves and restores the window configuration. That takes some time, so if your program does not care what happens to the window configurations, it is better to set this variable tonil.If the value is a list, only the listed windows are saved and restored.
You can use the W command in Edebug to change this variable interactively. See Edebug Display Update.
If this is non-
nil, Edebug saves and restores point in all displayed buffers.Saving and restoring point in other buffers is necessary if you are debugging code that changes the point of a buffer which is displayed in a non-selected window. If Edebug or the user then selects the window, point in that buffer will move to the window's value of point.
Saving and restoring point in all buffers is expensive, since it requires selecting each window twice, so enable this only if you need it. See Edebug Display Update.
If this variable is non-
nil, it specifies the initial execution mode for Edebug when it is first activated. Possible values arestep,next,go,Go-nonstop,trace,Trace-fast,continue, andContinue-fast.The default value is
step. See Edebug Execution Modes.
Non-
nilmeans display a trace of function entry and exit. Tracing output is displayed in a buffer named ‘*edebug-trace*’, one function entry or exit per line, indented by the recursion level.The default value is
nil.Also see
edebug-tracing, in Trace Buffer.
If non-
nil, Edebug tests coverage of all expressions debugged. See Coverage Testing.
If non-
nil, continue defining or executing any keyboard macro that is executing outside of Edebug. Use this with caution since it is not debugged. See Edebug Execution Modes.
Edebug binds
debug-on-errorto this value, ifdebug-on-errorwas previouslynil. See Trapping Errors.
Edebug binds
debug-on-quitto this value, ifdebug-on-quitwas previouslynil. See Trapping Errors.
If you change the values of edebug-on-error or
edebug-on-quit while Edebug is active, their values won't be used
until the next time Edebug is invoked via a new command.
If non-
nil, an expression to test for at every stop point. If the result is non-nil, then break. Errors are ignored. See Global Break Condition.
The Lisp reader reports invalid syntax, but cannot say where the real problem is. For example, the error “End of file during parsing” in evaluating an expression indicates an excess of open parentheses (or square brackets). The reader detects this imbalance at the end of the file, but it cannot figure out where the close parenthesis should have been. Likewise, “Invalid read syntax: ")"” indicates an excess close parenthesis or missing open parenthesis, but does not say where the missing parenthesis belongs. How, then, to find what to change?
If the problem is not simply an imbalance of parentheses, a useful technique is to try C-M-e at the beginning of each defun, and see if it goes to the place where that defun appears to end. If it does not, there is a problem in that defun.
However, unmatched parentheses are the most common syntax errors in Lisp, and we can give further advice for those cases. (In addition, just moving point through the code with Show Paren mode enabled might find the mismatch.)
The first step is to find the defun that is unbalanced. If there is an excess open parenthesis, the way to do this is to go to the end of the file and type C-u C-M-u. This will move you to the beginning of the defun that is unbalanced.
The next step is to determine precisely what is wrong. There is no way to be sure of this except by studying the program, but often the existing indentation is a clue to where the parentheses should have been. The easiest way to use this clue is to reindent with C-M-q and see what moves. But don't do this yet! Keep reading, first.
Before you do this, make sure the defun has enough close parentheses. Otherwise, C-M-q will get an error, or will reindent all the rest of the file until the end. So move to the end of the defun and insert a close parenthesis there. Don't use C-M-e to move there, since that too will fail to work until the defun is balanced.
Now you can go to the beginning of the defun and type C-M-q. Usually all the lines from a certain point to the end of the function will shift to the right. There is probably a missing close parenthesis, or a superfluous open parenthesis, near that point. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses.
After you think you have fixed the problem, use C-M-q again. If the old indentation actually fit the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything.
To deal with an excess close parenthesis, first go to the beginning of the file, then type C-u -1 C-M-u to find the end of the unbalanced defun.
Then find the actual matching close parenthesis by typing C-M-f at the beginning of that defun. This will leave you somewhere short of the place where the defun ought to end. It is possible that you will find a spurious close parenthesis in that vicinity.
If you don't see a problem at that point, the next thing to do is to type C-M-q at the beginning of the defun. A range of lines will probably shift left; if so, the missing open parenthesis or spurious close parenthesis is probably near the first of those lines. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses.
After you think you have fixed the problem, use C-M-q again. If the old indentation actually fits the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything.
When an error happens during byte compilation, it is normally due to invalid syntax in the program you are compiling. The compiler prints a suitable error message in the ‘*Compile-Log*’ buffer, and then stops. The message may state a function name in which the error was found, or it may not. Either way, here is how to find out where in the file the error occurred.
What you should do is switch to the buffer ‘ *Compiler Input*’. (Note that the buffer name starts with a space, so it does not show up in M-x list-buffers.) This buffer contains the program being compiled, and point shows how far the byte compiler was able to read.
If the error was due to invalid Lisp syntax, point shows exactly where the invalid syntax was detected. The cause of the error is not necessarily near by! Use the techniques in the previous section to find the error.
If the error was detected while compiling a form that had been read successfully, then point is located at the end of the form. In this case, this technique can't localize the error precisely, but can still show you which function to check.
Printing and reading are the operations of converting Lisp objects to textual form and vice versa. They use the printed representations and read syntax described in Lisp Data Types.
This chapter describes the Lisp functions for reading and printing. It also describes streams, which specify where to get the text (if reading) or where to put it (if printing).
Reading a Lisp object means parsing a Lisp expression in textual
form and producing a corresponding Lisp object. This is how Lisp
programs get into Lisp from files of Lisp code. We call the text the
read syntax of the object. For example, the text ‘(a . 5)’
is the read syntax for a cons cell whose car is a and whose
cdr is the number 5.
Printing a Lisp object means producing text that represents that object—converting the object to its printed representation (see Printed Representation). Printing the cons cell described above produces the text ‘(a . 5)’.
Reading and printing are more or less inverse operations: printing the
object that results from reading a given piece of text often produces
the same text, and reading the text that results from printing an object
usually produces a similar-looking object. For example, printing the
symbol foo produces the text ‘foo’, and reading that text
returns the symbol foo. Printing a list whose elements are
a and b produces the text ‘(a b)’, and reading that
text produces a list (but not the same list) with elements a
and b.
However, these two operations are not precisely inverse to each other. There are three kinds of exceptions:
Most of the Lisp functions for reading text take an input stream as an argument. The input stream specifies where or how to get the characters of the text to be read. Here are the possible types of input stream:
tt used as a stream means that the input is read from the
minibuffer. In fact, the minibuffer is invoked once and the text
given by the user is made into a string that is then used as the
input stream. If Emacs is running in batch mode, standard input is used
instead of the minibuffer. For example,
(message "%s" (read t))
will read a Lisp expression from standard input and print the result
to standard output.
nilnil supplied as an input stream means to use the value of
standard-input instead; that value is the default input
stream, and must be a non-nil input stream.
Here is an example of reading from a stream that is a buffer, showing where point is located before and after:
---------- Buffer: foo ----------
This-!- is the contents of foo.
---------- Buffer: foo ----------
(read (get-buffer "foo"))
=> is
(read (get-buffer "foo"))
=> the
---------- Buffer: foo ----------
This is the-!- contents of foo.
---------- Buffer: foo ----------
Note that the first read skips a space. Reading skips any amount of whitespace preceding the significant text.
Here is an example of reading from a stream that is a marker,
initially positioned at the beginning of the buffer shown. The value
read is the symbol This.
---------- Buffer: foo ----------
This is the contents of foo.
---------- Buffer: foo ----------
(setq m (set-marker (make-marker) 1 (get-buffer "foo")))
=> #<marker at 1 in foo>
(read m)
=> This
m
=> #<marker at 5 in foo> ;; Before the first space.
Here we read from the contents of a string:
(read "(When in) the course")
=> (When in)
The following example reads from the minibuffer. The
prompt is: ‘Lisp expression: ’. (That is always the prompt
used when you read from the stream t.) The user's input is shown
following the prompt.
(read t)
=> 23
---------- Buffer: Minibuffer ----------
Lisp expression: 23 <RET>
---------- Buffer: Minibuffer ----------
Finally, here is an example of a stream that is a function, named
useless-stream. Before we use the stream, we initialize the
variable useless-list to a list of characters. Then each call to
the function useless-stream obtains the next character in the list
or unreads a character by adding it to the front of the list.
(setq useless-list (append "XY()" nil))
=> (88 89 40 41)
(defun useless-stream (&optional unread)
(if unread
(setq useless-list (cons unread useless-list))
(prog1 (car useless-list)
(setq useless-list (cdr useless-list)))))
=> useless-stream
Now we read using the stream thus constructed:
(read 'useless-stream)
=> XY
useless-list
=> (40 41)
Note that the open and close parentheses remain in the list. The Lisp
reader encountered the open parenthesis, decided that it ended the
input, and unread it. Another attempt to read from the stream at this
point would read ‘()’ and return nil.
This function is used internally as an input stream to read from the input file opened by the function
load. Don't use this function yourself.
This section describes the Lisp functions and variables that pertain to reading.
In the functions below, stream stands for an input stream (see
the previous section). If stream is nil or omitted, it
defaults to the value of standard-input.
An end-of-file error is signaled if reading encounters an
unterminated list, vector, or string.
This function reads one textual Lisp expression from stream, returning it as a Lisp object. This is the basic Lisp input function.
This function reads the first textual Lisp expression from the text in string. It returns a cons cell whose car is that expression, and whose cdr is an integer giving the position of the next remaining character in the string (i.e., the first one not read).
If start is supplied, then reading begins at index start in the string (where the first character is at index 0). If you specify end, then reading is forced to stop just before that index, as if the rest of the string were not there.
For example:
(read-from-string "(setq x 55) (setq y 5)") => ((setq x 55) . 11) (read-from-string "\"A short string\"") => ("A short string" . 16) ;; Read starting at the first character. (read-from-string "(list 112)" 0) => ((list 112) . 10) ;; Read starting at the second character. (read-from-string "(list 112)" 1) => (list . 5) ;; Read starting at the seventh character, ;; and stopping at the ninth. (read-from-string "(list 112)" 6 8) => (11 . 8)
This variable holds the default input stream—the stream that
readuses when the stream argument isnil.
An output stream specifies what to do with the characters produced by printing. Most print functions accept an output stream as an optional argument. Here are the possible types of output stream:
tnilnil specified as an output stream means to use the value of
standard-output instead; that value is the default output
stream, and must not be nil.
Many of the valid output streams are also valid as input streams. The difference between input and output streams is therefore more a matter of how you use a Lisp object, than of different types of object.
Here is an example of a buffer used as an output stream. Point is initially located as shown immediately before the ‘h’ in ‘the’. At the end, point is located directly before that same ‘h’.
---------- Buffer: foo ----------
This is t-!-he contents of foo.
---------- Buffer: foo ----------
(print "This is the output" (get-buffer "foo"))
=> "This is the output"
---------- Buffer: foo ----------
This is t
"This is the output"
-!-he contents of foo.
---------- Buffer: foo ----------
Now we show a use of a marker as an output stream. Initially, the
marker is in buffer foo, between the ‘t’ and the ‘h’ in
the word ‘the’. At the end, the marker has advanced over the
inserted text so that it remains positioned before the same ‘h’.
Note that the location of point, shown in the usual fashion, has no
effect.
---------- Buffer: foo ----------
This is the -!-output
---------- Buffer: foo ----------
(setq m (copy-marker 10))
=> #<marker at 10 in foo>
(print "More output for foo." m)
=> "More output for foo."
---------- Buffer: foo ----------
This is t
"More output for foo."
he -!-output
---------- Buffer: foo ----------
m
=> #<marker at 34 in foo>
The following example shows output to the echo area:
(print "Echo Area output" t)
=> "Echo Area output"
---------- Echo Area ----------
"Echo Area output"
---------- Echo Area ----------
Finally, we show the use of a function as an output stream. The
function eat-output takes each character that it is given and
conses it onto the front of the list last-output (see Building Lists). At the end, the list contains all the characters output, but
in reverse order.
(setq last-output nil)
=> nil
(defun eat-output (c)
(setq last-output (cons c last-output)))
=> eat-output
(print "This is the output" 'eat-output)
=> "This is the output"
last-output
=> (10 34 116 117 112 116 117 111 32 101 104
116 32 115 105 32 115 105 104 84 34 10)
Now we can put the output in the proper order by reversing the list:
(concat (nreverse last-output))
=> "
\"This is the output\"
"
Calling concat converts the list to a string so you can see its
contents more clearly.
This section describes the Lisp functions for printing Lisp objects—converting objects into their printed representation.
Some of the Emacs printing functions add quoting characters to the output when necessary so that it can be read properly. The quoting characters used are ‘"’ and ‘\’; they distinguish strings from symbols, and prevent punctuation characters in strings and symbols from being taken as delimiters when reading. See Printed Representation, for full details. You specify quoting or no quoting by the choice of printing function.
If the text is to be read back into Lisp, then you should print with quoting characters to avoid ambiguity. Likewise, if the purpose is to describe a Lisp object clearly for a Lisp programmer. However, if the purpose of the output is to look nice for humans, then it is usually better to print without quoting.
Lisp objects can refer to themselves. Printing a self-referential object in the normal way would require an infinite amount of text, and the attempt could cause infinite recursion. Emacs detects such recursion and prints ‘#level’ instead of recursively printing an object already being printed. For example, here ‘#0’ indicates a recursive reference to the object at level 0 of the current print operation:
(setq foo (list nil))
=> (nil)
(setcar foo foo)
=> (#0)
In the functions below, stream stands for an output stream.
(See the previous section for a description of output streams.) If
stream is nil or omitted, it defaults to the value of
standard-output.
The
(progn (print 'The\ cat\ in) (print "the hat") (print " came back")) -| -| The\ cat\ in -| -| "the hat" -| -| " came back" -| => " came back"
This function outputs the printed representation of object to stream. It does not print newlines to separate output as
(progn (prin1 'The\ cat\ in) (prin1 "the hat") (prin1 " came back")) -| The\ cat\ in"the hat"" came back" => " came back"
This function outputs the printed representation of object to stream. It returns object.
This function is intended to produce output that is readable by people, not by
read, so it doesn't insert quoting characters and doesn't put double-quotes around the contents of strings. It does not add any spacing between calls.(progn (princ 'The\ cat) (princ " in the \"hat\"")) -| The cat in the "hat" => " in the \"hat\""
This function outputs a newline to stream. The name stands for “terminate print”.
This function outputs character to stream. It returns character.
This function returns a string containing the text that
prin1would have printed for the same argument.(prin1-to-string 'foo) => "foo" (prin1-to-string (mark-marker)) => "#<marker at 2773 in strings.texi>"If noescape is non-
nil, that inhibits use of quoting characters in the output. (This argument is supported in Emacs versions 19 and later.)(prin1-to-string "foo") => "\"foo\"" (prin1-to-string "foo" t) => "foo"See
format, in String Conversion, for other ways to obtain the printed representation of a Lisp object as a string.
This macro executes the body forms with
standard-outputset up to feed output into a string. Then it returns that string.For example, if the current buffer name is ‘foo’,
(with-output-to-string (princ "The buffer is ") (princ (buffer-name)))returns
"The buffer is foo".
The value of this variable is the default output stream—the stream that print functions use when the stream argument is
nil.
If this variable is non-
nil, then newline characters in strings are printed as ‘\n’ and formfeeds are printed as ‘\f’. Normally these characters are printed as actual newlines and formfeeds.This variable affects the print functions
prin1andprinc. Here is an example usingprin1:(prin1 "a\nb") -| "a -| b" => "a b" (let ((print-escape-newlines t)) (prin1 "a\nb")) -| "a\nb" => "a b"In the second expression, the local binding of
print-escape-newlinesis in effect during the call toprin1, but not during the printing of the result.
If this variable is non-
nil, then unibyte non-ascii characters in strings are unconditionally printed as backslash sequences by the print functionsprin1andThose functions also use backslash sequences for unibyte non-ascii characters, regardless of the value of this variable, when the output stream is a multibyte buffer or a marker pointing into one.
If this variable is non-
nil, then multibyte non-ascii characters in strings are unconditionally printed as backslash sequences by the print functionsprin1andThose functions also use backslash sequences for multibyte non-ascii characters, regardless of the value of this variable, when the output stream is a unibyte buffer or a marker pointing into one.
The value of this variable is the maximum number of elements to print in any list, vector or bool-vector. If an object being printed has more than this many elements, it is abbreviated with an ellipsis.
If the value is
nil(the default), then there is no limit.(setq print-length 2) => 2 (print '(1 2 3 4 5)) -| (1 2 ...) => (1 2 ...)
The value of this variable is the maximum depth of nesting of parentheses and brackets when printed. Any list or vector at a depth exceeding this limit is abbreviated with an ellipsis. A value of
nil(which is the default) means no limit.
These variables are used for detecting and reporting circular and shared structure—but they are only defined in Emacs 21.
If non-
nil, this variable enables detection of circular and shared structure in printing.
If non-
nil, this variable enables detection of uninterned symbols (see Creating Symbols) in printing. When this is enabled, uninterned symbols print with the prefix ‘#:’, which tells the Lisp reader to produce an uninterned symbol.
A minibuffer is a special buffer that Emacs commands use to read arguments more complicated than the single numeric prefix argument. These arguments include file names, buffer names, and command names (as in M-x). The minibuffer is displayed on the bottom line of the frame, in the same place as the echo area, but only while it is in use for reading an argument.
In most ways, a minibuffer is a normal Emacs buffer. Most operations within a buffer, such as editing commands, work normally in a minibuffer. However, many operations for managing buffers do not apply to minibuffers. The name of a minibuffer always has the form ‘ *Minibuf-number’, and it cannot be changed. Minibuffers are displayed only in special windows used only for minibuffers; these windows always appear at the bottom of a frame. (Sometimes frames have no minibuffer window, and sometimes a special kind of frame contains nothing but a minibuffer window; see Minibuffers and Frames.)
The text in the minibuffer always starts with the prompt string,
the text that was specified by the program that is using the minibuffer
to tell the user what sort of input to type. This text is marked
read-only so you won't accidentally delete or change it. It is also
marked as a field (see Fields), so that certain motion functions,
including beginning-of-line, forward-word,
forward-sentence, and forward-paragraph, stop at the
boundary between the prompt and the actual text. (In older Emacs
versions, the prompt was displayed using a special mechanism and was not
part of the buffer contents.)
The minibuffer's window is normally a single line; it grows automatically if necessary if the contents require more space. You can explicitly resize it temporarily with the window sizing commands; it reverts to its normal size when the minibuffer is exited. You can resize it permanently by using the window sizing commands in the frame's other window, when the minibuffer is not active. If the frame contains just a minibuffer, you can change the minibuffer's size by changing the frame's size.
If a command uses a minibuffer while there is an active minibuffer,
this is called a recursive minibuffer. The first minibuffer is
named ‘ *Minibuf-0*’. Recursive minibuffers are named by
incrementing the number at the end of the name. (The names begin with a
space so that they won't show up in normal buffer lists.) Of several
recursive minibuffers, the innermost (or most recently entered) is the
active minibuffer. We usually call this “the” minibuffer. You can
permit or forbid recursive minibuffers by setting the variable
enable-recursive-minibuffers or by putting properties of that
name on command symbols (see Minibuffer Misc).
Like other buffers, a minibuffer may use any of several local keymaps (see Keymaps); these contain various exit commands and in some cases completion commands (see Completion).
minibuffer-local-map is for ordinary input (no completion).
minibuffer-local-ns-map is similar, except that <SPC> exits
just like <RET>. This is used mainly for Mocklisp compatibility.
minibuffer-local-completion-map is for permissive completion.
minibuffer-local-must-match-map is for strict completion and
for cautious completion.
When Emacs is running in batch mode, any request to read from the minibuffer actually reads a line from the standard input descriptor that was supplied when Emacs was started.
Most often, the minibuffer is used to read text as a string. It can
also be used to read a Lisp object in textual form. The most basic
primitive for minibuffer input is read-from-minibuffer; it can do
either one.
In most cases, you should not call minibuffer input functions in the
middle of a Lisp function. Instead, do all minibuffer input as part of
reading the arguments for a command, in the interactive
specification. See Defining Commands.
This function is the most general way to get input through the minibuffer. By default, it accepts arbitrary text and returns it as a string; however, if read is non-
nil, then it usesreadto convert the text into a Lisp object (see Input Functions).The first thing this function does is to activate a minibuffer and display it with prompt-string as the prompt. This value must be a string. Then the user can edit text in the minibuffer.
When the user types a command to exit the minibuffer,
read-from-minibufferconstructs the return value from the text in the minibuffer. Normally it returns a string containing that text. However, if read is non-nil,read-from-minibufferreads the text and returns the resulting Lisp object, unevaluated. (See Input Functions, for information about reading.)The argument default specifies a default value to make available through the history commands. It should be a string, or
nil. If read is non-nil, then default is also used as the input toread, if the user enters empty input. However, in the usual case (where read isnil),read-from-minibufferdoes not return default when the user enters empty input; it returns an empty string,"". In this respect, it is different from all the other minibuffer input functions in this chapter.If keymap is non-
nil, that keymap is the local keymap to use in the minibuffer. If keymap is omitted ornil, the value ofminibuffer-local-mapis used as the keymap. Specifying a keymap is the most important way to customize the minibuffer for various applications such as completion.The argument hist specifies which history list variable to use for saving the input and for history commands used in the minibuffer. It defaults to
minibuffer-history. See Minibuffer History.If the variable
minibuffer-allow-text-propertiesis non-nil, then the string which is returned includes whatever text properties were present in the minibuffer. Otherwise all the text properties are stripped when the value is returned.If the argument inherit-input-method is non-
nil, then the minibuffer inherits the current input method (see Input Methods) and the setting ofenable-multibyte-characters(see Text Representations) from whichever buffer was current before entering the minibuffer.If initial-contents is a string,
read-from-minibufferinserts it into the minibuffer, leaving point at the end, before the user starts to edit the text. The minibuffer appears with this text as its initial contents.Alternatively, initial-contents can be a cons cell of the form
(string.position). This means to insert string in the minibuffer but put point position characters from the beginning, rather than at the end.Usage note: The initial-contents argument and the default argument are two alternative features for more or less the same job. It does not make sense to use both features in a single call to
read-from-minibuffer. In general, we recommend using default, since this permits the user to insert the default value when it is wanted, but does not burden the user with deleting it from the minibuffer on other occasions.
This function reads a string from the minibuffer and returns it. The arguments prompt and initial are used as in
read-from-minibuffer. The keymap used isminibuffer-local-map.The optional argument history, if non-nil, specifies a history list and optionally the initial position in the list. The optional argument default specifies a default value to return if the user enters null input; it should be a string. The optional argument inherit-input-method specifies whether to inherit the current buffer's input method.
This function is a simplified interface to the
read-from-minibufferfunction:(read-string prompt initial history default inherit) == (let ((value (read-from-minibuffer prompt initial nil nil history default inherit))) (if (equal value "") default value))
If this variable is
nil, thenread-from-minibufferstrips all text properties from the minibuffer input before returning it. Since all minibuffer input usesread-from-minibuffer, this variable applies to all minibuffer input.Note that the completion functions discard text properties unconditionally, regardless of the value of this variable.
This is the default local keymap for reading from the minibuffer. By default, it makes the following bindings:
- C-j
exit-minibuffer- <RET>
exit-minibuffer- C-g
abort-recursive-edit- M-n
next-history-element- M-p
previous-history-element- M-r
next-matching-history-element- M-s
previous-matching-history-element
This function reads a string from the minibuffer, but does not allow whitespace characters as part of the input: instead, those characters terminate the input. The arguments prompt, initial, and inherit-input-method are used as in
read-from-minibuffer.This is a simplified interface to the
read-from-minibufferfunction, and passes the value of theminibuffer-local-ns-mapkeymap as the keymap argument for that function. Since the keymapminibuffer-local-ns-mapdoes not rebind C-q, it is possible to put a space into the string, by quoting it.(read-no-blanks-input prompt initial) == (read-from-minibuffer prompt initial minibuffer-local-ns-map)
This built-in variable is the keymap used as the minibuffer local keymap in the function
read-no-blanks-input. By default, it makes the following bindings, in addition to those ofminibuffer-local-map:
This section describes functions for reading Lisp objects with the minibuffer.
This function reads a Lisp object using the minibuffer, and returns it without evaluating it. The arguments prompt and initial are used as in
read-from-minibuffer.This is a simplified interface to the
read-from-minibufferfunction:(read-minibuffer prompt initial) == (read-from-minibuffer prompt initial nil t)Here is an example in which we supply the string
"(testing)"as initial input:(read-minibuffer "Enter an expression: " (format "%s" '(testing))) ;; Here is how the minibuffer is displayed: ---------- Buffer: Minibuffer ---------- Enter an expression: (testing)-!- ---------- Buffer: Minibuffer ----------The user can type <RET> immediately to use the initial input as a default, or can edit the input.
This function reads a Lisp expression using the minibuffer, evaluates it, then returns the result. The arguments prompt and initial are used as in
read-from-minibuffer.This function simply evaluates the result of a call to
read-minibuffer:(eval-minibuffer prompt initial) == (eval (read-minibuffer prompt initial))
This function reads a Lisp expression in the minibuffer, and then evaluates it. The difference between this command and
eval-minibufferis that here the initial form is not optional and it is treated as a Lisp object to be converted to printed representation rather than as a string of text. It is printed withprin1, so if it is a string, double-quote characters (‘"’) appear in the initial text. See Output Functions.The first thing
edit-and-eval-commanddoes is to activate the minibuffer with prompt as the prompt. Then it inserts the printed representation of form in the minibuffer, and lets the user edit it. When the user exits the minibuffer, the edited text is read withreadand then evaluated. The resulting value becomes the value ofedit-and-eval-command.In the following example, we offer the user an expression with initial text which is a valid form already:
(edit-and-eval-command "Please edit: " '(forward-word 1)) ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- Please edit: (forward-word 1)-!- ---------- Buffer: Minibuffer ----------Typing <RET> right away would exit the minibuffer and evaluate the expression, thus moving point forward one word.
edit-and-eval-commandreturnsnilin this example.
A minibuffer history list records previous minibuffer inputs so the user can reuse them conveniently. A history list is actually a symbol, not a list; it is a variable whose value is a list of strings (previous inputs), most recent first.
There are many separate history lists, used for different kinds of inputs. It's the Lisp programmer's job to specify the right history list for each use of the minibuffer.
The basic minibuffer input functions read-from-minibuffer and
completing-read both accept an optional argument named hist
which is how you specify the history list. Here are the possible
values:
If you specify startpos, then you should also specify that element of the history as the initial minibuffer contents, for consistency.
If you don't specify hist, then the default history list
minibuffer-history is used. For other standard history lists,
see below. You can also create your own history list variable; just
initialize it to nil before the first use.
Both read-from-minibuffer and completing-read add new
elements to the history list automatically, and provide commands to
allow the user to reuse items on the list. The only thing your program
needs to do to use a history list is to initialize it and to pass its
name to the input functions when you wish. But it is safe to modify the
list by hand when the minibuffer input functions are not using it.
Here are some of the standard minibuffer history list variables:
A history list for arguments to
query-replace(and similar arguments to other commands).
A history list for arguments that are names of extended commands.
A history list for arguments that are Lisp expressions to evaluate.
Completion is a feature that fills in the rest of a name
starting from an abbreviation for it. Completion works by comparing the
user's input against a list of valid names and determining how much of
the name is determined uniquely by what the user has typed. For
example, when you type C-x b (switch-to-buffer) and then
type the first few letters of the name of the buffer to which you wish
to switch, and then type <TAB> (minibuffer-complete), Emacs
extends the name as far as it can.
Standard Emacs commands offer completion for names of symbols, files, buffers, and processes; with the functions in this section, you can implement completion for other kinds of names.
The try-completion function is the basic primitive for
completion: it returns the longest determined completion of a given
initial string, with a given set of strings to match against.
The function completing-read provides a higher-level interface
for completion. A call to completing-read specifies how to
determine the list of valid names. The function then activates the
minibuffer with a local keymap that binds a few keys to commands useful
for completion. Other functions provide convenient simple interfaces
for reading certain kinds of names with completion.
The two functions try-completion and all-completions
have nothing in themselves to do with minibuffers. We describe them in
this chapter so as to keep them near the higher-level completion
features that do use the minibuffer.
This function returns the longest common substring of all possible completions of string in collection. The value of collection must be an alist, an obarray, or a function that implements a virtual set of strings (see below).
Completion compares string against each of the permissible completions specified by collection; if the beginning of the permissible completion equals string, it matches. If no permissible completions match,
try-completionreturnsnil. If only one permissible completion matches, and the match is exact, thentry-completionreturnst. Otherwise, the value is the longest initial sequence common to all the permissible completions that match.If collection is an alist (see Association Lists), the cars of the alist elements form the set of permissible completions.
If collection is an obarray (see Creating Symbols), the names of all symbols in the obarray form the set of permissible completions. The global variable
obarrayholds an obarray containing the names of all interned Lisp symbols.Note that the only valid way to make a new obarray is to create it empty and then add symbols to it one by one using
intern. Also, you cannot intern a given symbol in more than one obarray.If the argument predicate is non-
nil, then it must be a function of one argument. It is used to test each possible match, and the match is accepted only if predicate returns non-nil. The argument given to predicate is either a cons cell from the alist (the car of which is a string) or else it is a symbol (not a symbol name) from the obarray.You can also use a symbol that is a function as collection. Then the function is solely responsible for performing completion;
try-completionreturns whatever this function returns. The function is called with three arguments: string, predicate andnil. (The reason for the third argument is so that the same function can be used inall-completionsand do the appropriate thing in either case.) See Programmed Completion.In the first of the following examples, the string ‘foo’ is matched by three of the alist cars. All of the matches begin with the characters ‘fooba’, so that is the result. In the second example, there is only one possible match, and it is exact, so the value is
t.(try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))) => "fooba" (try-completion "foo" '(("barfoo" 2) ("foo" 3))) => tIn the following example, numerous symbols begin with the characters ‘forw’, and all of them begin with the word ‘forward’. In most of the symbols, this is followed with a ‘-’, but not in all, so no more than ‘forward’ can be completed.
(try-completion "forw" obarray) => "forward"Finally, in the following example, only two of the three possible matches pass the predicate
test(the string ‘foobaz’ is too short). Both of those begin with the string ‘foobar’.(defun test (s) (> (length (car s)) 6)) => test (try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) => "foobar"
This function returns a list of all possible completions of string. The arguments to this function (aside from nospace) are the same as those of
try-completion. If nospace is non-nil, completions that start with a space are ignored unless string also starts with a space.If collection is a function, it is called with three arguments: string, predicate and
t; thenall-completionsreturns whatever the function returns. See Programmed Completion.Here is an example, using the function
testshown in the example fortry-completion:(defun test (s) (> (length (car s)) 6)) => test (all-completions "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) => ("foobar1" "foobar2")
If the value of this variable is non-
nil, Emacs does not consider case significant in completion.
This section describes the basic interface for reading from the minibuffer with completion.
This function reads a string in the minibuffer, assisting the user by providing completion. It activates the minibuffer with prompt prompt, which must be a string.
The actual completion is done by passing collection and predicate to the function
try-completion. This happens in certain commands bound in the local keymaps used for completion.If require-match is
nil, the exit commands work regardless of the input in the minibuffer. If require-match ist, the usual minibuffer exit commands won't exit unless the input completes to an element of collection. If require-match is neithernilnort, then the exit commands won't exit unless the input already in the buffer matches an element of collection.However, empty input is always permitted, regardless of the value of require-match; in that case,
completing-readreturns default. The value of default (if non-nil) is also available to the user through the history commands.The user can exit with null input by typing <RET> with an empty minibuffer. Then
completing-readreturns"". This is how the user requests whatever default the command uses for the value being read. The user can return using <RET> in this way regardless of the value of require-match, and regardless of whether the empty string is included in collection.The function
completing-readworks by callingread-minibuffer. It usesminibuffer-local-completion-mapas the keymap if require-match isnil, and usesminibuffer-local-must-match-mapif require-match is non-nil. See Completion Commands.The argument hist specifies which history list variable to use for saving the input and for minibuffer history commands. It defaults to
minibuffer-history. See Minibuffer History.If initial is non-
nil,completing-readinserts it into the minibuffer as part of the input. Then it allows the user to edit the input, providing several commands to attempt completion. In most cases, we recommend using default, and not initial.We discourage use of a non-
nilvalue for initial, because it is an intrusive interface. The history list feature (which did not exist when we introduced initial) offers a far more convenient and general way for the user to get the default and edit it, and it is always available.If the argument inherit-input-method is non-
nil, then the minibuffer inherits the current input method (see Input Methods) and the setting ofenable-multibyte-characters(see Text Representations) from whichever buffer was current before entering the minibuffer.Completion ignores case when comparing the input against the possible matches, if the built-in variable
completion-ignore-caseis non-nil. See Basic Completion.Here's an example of using
completing-read:(completing-read "Complete a foo: " '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) nil t "fo") ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- Complete a foo: fo-!- ---------- Buffer: Minibuffer ----------If the user then types <DEL> <DEL> b <RET>,
completing-readreturnsbarfoo.The
completing-readfunction binds three variables to pass information to the commands that actually do completion. These variables areminibuffer-completion-table,minibuffer-completion-predicateandminibuffer-completion-confirm. For more information about them, see Completion Commands.
This section describes the keymaps, commands and user options used in the minibuffer to do completion.
completing-readuses this value as the local keymap when an exact match of one of the completions is not required. By default, this keymap makes the following bindings:
- ?
minibuffer-completion-help- <SPC>
minibuffer-complete-word- <TAB>
minibuffer-completewith other characters bound as in
minibuffer-local-map(see Text from Minibuffer).
completing-readuses this value as the local keymap when an exact match of one of the completions is required. Therefore, no keys are bound toexit-minibuffer, the command that exits the minibuffer unconditionally. By default, this keymap makes the following bindings:
- ?
minibuffer-completion-help- <SPC>
minibuffer-complete-word- <TAB>
minibuffer-complete- C-j
minibuffer-complete-and-exit- <RET>
minibuffer-complete-and-exitwith other characters bound as in
minibuffer-local-map.
The value of this variable is the alist or obarray used for completion in the minibuffer. This is the global variable that contains what
completing-readpasses totry-completion. It is used by minibuffer completion commands such asminibuffer-complete-word.
This variable's value is the predicate that
completing-readpasses totry-completion. The variable is also used by the other minibuffer completion functions.
This function completes the minibuffer contents by at most a single word. Even if the minibuffer contents have only one completion,
minibuffer-complete-worddoes not add any characters beyond the first character that is not a word constituent. See Syntax Tables.
This function completes the minibuffer contents, and exits if confirmation is not required, i.e., if
minibuffer-completion-confirmisnil. If confirmation is required, it is given by repeating this command immediately—the command is programmed to work without confirmation when run twice in succession.
When the value of this variable is non-
nil, Emacs asks for confirmation of a completion before exiting the minibuffer. The functionminibuffer-complete-and-exitchecks the value of this variable before it exits.
This function creates a list of the possible completions of the current minibuffer contents. It works by calling
all-completionsusing the value of the variableminibuffer-completion-tableas the collection argument, and the value ofminibuffer-completion-predicateas the predicate argument. The list of completions is displayed as text in a buffer named ‘*Completions*’.
This function displays completions to the stream in
standard-output, usually a buffer. (See Read and Print, for more information about streams.) The argument completions is normally a list of completions just returned byall-completions, but it does not have to be. Each element may be a symbol or a string, either of which is simply printed, or a list of two strings, which is printed as if the strings were concatenated.This function is called by
minibuffer-completion-help. The most common way to use it is together withwith-output-to-temp-buffer, like this:(with-output-to-temp-buffer "*Completions*" (display-completion-list (all-completions (buffer-string) my-alist)))
If this variable is non-
nil, the completion commands automatically display a list of possible completions whenever nothing can be completed because the next character is not uniquely determined.
This section describes the higher-level convenient functions for reading certain sorts of names with completion.
In most cases, you should not call these functions in the middle of a
Lisp function. When possible, do all minibuffer input as part of
reading the arguments for a command, in the interactive
specification. See Defining Commands.
This function reads the name of a buffer and returns it as a string. The argument default is the default name to use, the value to return if the user exits with an empty minibuffer. If non-
nil, it should be a string or a buffer. It is mentioned in the prompt, but is not inserted in the minibuffer as initial input.If existing is non-
nil, then the name specified must be that of an existing buffer. The usual commands to exit the minibuffer do not exit if the text is not valid, and <RET> does completion to attempt to find a valid name. (However, default is not checked for validity; it is returned, whatever it is, if the user exits with the minibuffer empty.)In the following example, the user enters ‘minibuffer.t’, and then types <RET>. The argument existing is
t, and the only buffer name starting with the given input is ‘minibuffer.texi’, so that name is the value.(read-buffer "Buffer name? " "foo" t) ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Buffer name? (default foo) -!- ---------- Buffer: Minibuffer ---------- ;; The user types minibuffer.t <RET>. => "minibuffer.texi"
This variable specifies how to read buffer names. For example, if you set this variable to
iswitchb-read-buffer, all Emacs commands that callread-bufferto read a buffer name will actually use theiswitchbpackage to read it.
This function reads the name of a command and returns it as a Lisp symbol. The argument prompt is used as in
read-from-minibuffer. Recall that a command is anything for whichcommandpreturnst, and a command name is a symbol for whichcommandpreturnst. See Interactive Call.The argument default specifies what to return if the user enters null input. It can be a symbol or a string; if it is a string,
read-commandinterns it before returning it. If default isnil, that means no default has been specified; then if the user enters null input, the return value isnil.(read-command "Command name? ") ;; After evaluation of the preceding expression, ;; the following prompt appears with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Command name? ---------- Buffer: Minibuffer ----------If the user types forward-c <RET>, then this function returns
forward-char.The
read-commandfunction is a simplified interface tocompleting-read. It uses the variableobarrayso as to complete in the set of extant Lisp symbols, and it uses thecommandppredicate so as to accept only command names:(read-command prompt) == (intern (completing-read prompt obarray 'commandp t nil))
This function reads the name of a user variable and returns it as a symbol.
The argument default specifies what to return if the user enters null input. It can be a symbol or a string; if it is a string,
read-variableinterns it before returning it. If default isnil, that means no default has been specified; then if the user enters null input, the return value isnil.(read-variable "Variable name? ") ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Variable name? -!- ---------- Buffer: Minibuffer ----------If the user then types fill-p <RET>,
read-variablereturnsfill-prefix.This function is similar to
read-command, but uses the predicateuser-variable-pinstead ofcommandp:(read-variable prompt) == (intern (completing-read prompt obarray 'user-variable-p t nil))
See also the functions read-coding-system and
read-non-nil-coding-system, in User-Chosen Coding Systems.
Here is another high-level completion function, designed for reading a file name. It provides special features including automatic insertion of the default directory.
This function reads a file name in the minibuffer, prompting with prompt and providing completion. If default is non-
nil, then the function returns default if the user just types <RET>. default is not checked for validity; it is returned, whatever it is, if the user exits with the minibuffer empty.If existing is non-
nil, then the user must specify the name of an existing file; <RET> performs completion to make the name valid if possible, and then refuses to exit if it is not valid. If the value of existing is neithernilnort, then <RET> also requires confirmation after completion. If existing isnil, then the name of a nonexistent file is acceptable.The argument directory specifies the directory to use for completion of relative file names. If
insert-default-directoryis non-nil, directory is also inserted in the minibuffer as initial input. It defaults to the current buffer's value ofdefault-directory.If you specify initial, that is an initial file name to insert in the buffer (after directory, if that is inserted). In this case, point goes at the beginning of initial. The default for initial is
nil—don't insert any file name. To see what initial does, try the command C-x C-v. Note: we recommend using default rather than initial in most cases.Here is an example:
(read-file-name "The file is ") ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/-!- ---------- Buffer: Minibuffer ----------Typing manual <TAB> results in the following:
---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/manual.texi-!- ---------- Buffer: Minibuffer ----------If the user types <RET>,
read-file-namereturns the file name as the string"/gp/gnu/elisp/manual.texi".
This variable is used by
read-file-name. Its value controls whetherread-file-namestarts by placing the name of the default directory in the minibuffer, plus the initial file name if any. If the value of this variable isnil, thenread-file-namedoes not place any initial input in the minibuffer (unless you specify initial input with the initial argument). In that case, the default directory is still used for completion of relative file names, but is not displayed.For example:
;; Here the minibuffer starts out with the default directory. (let ((insert-default-directory t)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is ~lewis/manual/-!- ---------- Buffer: Minibuffer ---------- ;; Here the minibuffer is empty and only the prompt ;; appears on its line. (let ((insert-default-directory nil)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is -!- ---------- Buffer: Minibuffer ----------
Sometimes it is not possible to create an alist or an obarray containing all the intended possible completions. In such a case, you can supply your own function to compute the completion of a given string. This is called programmed completion.
To use this feature, pass a symbol with a function definition as the
collection argument to completing-read. The function
completing-read arranges to pass your completion function along
to try-completion and all-completions, which will then let
your function do all the work.
The completion function should accept three arguments:
nil if
none. Your function should call the predicate for each possible match,
and ignore the possible match if the predicate returns nil.
There are three flag values for three operations:
nil specifies try-completion. The completion function
should return the completion of the specified string, or t if the
string is a unique and exact match already, or nil if the string
matches no possibility.
If the string is an exact match for one possibility, but also matches
other longer possibilities, the function should return the string, not
t.
t specifies all-completions. The completion function
should return a list of all possible completions of the specified
string.
lambda specifies a test for an exact match. The completion
function should return t if the specified string is an exact
match for some possibility; nil otherwise.
It would be consistent and clean for completion functions to allow lambda expressions (lists that are functions) as well as function symbols as collection, but this is impossible. Lists as completion tables are already assigned another meaning—as alists. It would be unreliable to fail to handle an alist normally because it is also a possible function. So you must arrange for any function you wish to use for completion to be encapsulated in a symbol.
Emacs uses programmed completion when completing file names. See File Name Completion.
This section describes functions used to ask the user a yes-or-no
question. The function y-or-n-p can be answered with a single
character; it is useful for questions where an inadvertent wrong answer
will not have serious consequences. yes-or-no-p is suitable for
more momentous questions, since it requires three or four characters to
answer.
If either of these functions is called in a command that was invoked
using the mouse—more precisely, if last-nonmenu-event
(see Command Loop Info) is either nil or a list—then it
uses a dialog box or pop-up menu to ask the question. Otherwise, it
uses keyboard input. You can force use of the mouse or use of keyboard
input by binding last-nonmenu-event to a suitable value around
the call.
Strictly speaking, yes-or-no-p uses the minibuffer and
y-or-n-p does not; but it seems best to describe them together.
This function asks the user a question, expecting input in the echo area. It returns
tif the user types y,nilif the user types n. This function also accepts <SPC> to mean yes and <DEL> to mean no. It accepts C-] to mean “quit”, like C-g, because the question might look like a minibuffer and for that reason the user might try to use C-] to get out. The answer is a single character, with no <RET> needed to terminate it. Upper and lower case are equivalent.“Asking the question” means printing prompt in the echo area, followed by the string ‘(y or n) ’. If the input is not one of the expected answers (y, n, <SPC>, <DEL>, or something that quits), the function responds ‘Please answer y or n.’, and repeats the request.
This function does not actually use the minibuffer, since it does not allow editing of the answer. It actually uses the echo area (see The Echo Area), which uses the same screen space as the minibuffer. The cursor moves to the echo area while the question is being asked.
The answers and their meanings, even ‘y’ and ‘n’, are not hardwired. The keymap
query-replace-mapspecifies them. See Search and Replace.In the following example, the user first types q, which is invalid. At the next prompt the user types y.
(y-or-n-p "Do you need a lift? ") ;; After evaluation of the preceding expression, ;; the following prompt appears in the echo area: ---------- Echo area ---------- Do you need a lift? (y or n) ---------- Echo area ---------- ;; If the user then types q, the following appears: ---------- Echo area ---------- Please answer y or n. Do you need a lift? (y or n) ---------- Echo area ---------- ;; When the user types a valid answer, ;; it is displayed after the question: ---------- Echo area ---------- Do you need a lift? (y or n) y ---------- Echo area ----------We show successive lines of echo area messages, but only one actually appears on the screen at a time.
Like
y-or-n-p, except that if the user fails to answer within seconds seconds, this function stops waiting and returns default-value. It works by setting up a timer; see Timers. The argument seconds may be an integer or a floating point number.
This function asks the user a question, expecting input in the minibuffer. It returns
tif the user enters ‘yes’,nilif the user types ‘no’. The user must type <RET> to finalize the response. Upper and lower case are equivalent.
yes-or-no-pstarts by displaying prompt in the echo area, followed by ‘(yes or no) ’. The user must type one of the expected responses; otherwise, the function responds ‘Please answer yes or no.’, waits about two seconds and repeats the request.
yes-or-no-prequires more work from the user thany-or-n-pand is appropriate for more crucial decisions.Here is an example:
(yes-or-no-p "Do you really want to remove everything? ") ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: minibuffer ---------- Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------If the user first types y <RET>, which is invalid because this function demands the entire word ‘yes’, it responds by displaying these prompts, with a brief pause between them:
---------- Buffer: minibuffer ---------- Please answer yes or no. Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------
When you have a series of similar questions to ask, such as “Do you
want to save this buffer” for each buffer in turn, you should use
map-y-or-n-p to ask the collection of questions, rather than
asking each question individually. This gives the user certain
convenient facilities such as the ability to answer the whole series at
once.
This function asks the user a series of questions, reading a single-character answer in the echo area for each one.
The value of list specifies the objects to ask questions about. It should be either a list of objects or a generator function. If it is a function, it should expect no arguments, and should return either the next object to ask about, or
nilmeaning stop asking questions.The argument prompter specifies how to ask each question. If prompter is a string, the question text is computed like this:
(format prompter object)where object is the next object to ask about (as obtained from list).
If not a string, prompter should be a function of one argument (the next object to ask about) and should return the question text. If the value is a string, that is the question to ask the user. The function can also return
tmeaning do act on this object (and don't ask the user), ornilmeaning ignore this object (and don't ask the user).The argument actor says how to act on the answers that the user gives. It should be a function of one argument, and it is called with each object that the user says yes for. Its argument is always an object obtained from list.
If the argument help is given, it should be a list of this form:
(singular plural action)where singular is a string containing a singular noun that describes the objects conceptually being acted on, plural is the corresponding plural noun, and action is a transitive verb describing what actor does.
If you don't specify help, the default is
("object" "objects" "act on").Each time a question is asked, the user may enter y, Y, or <SPC> to act on that object; n, N, or <DEL> to skip that object; ! to act on all following objects; <ESC> or q to exit (skip all following objects); . (period) to act on the current object and then exit; or C-h to get help. These are the same answers that
query-replaceaccepts. The keymapquery-replace-mapdefines their meaning formap-y-or-n-pas well as forquery-replace; see Search and Replace.You can use action-alist to specify additional possible answers and what they mean. It is an alist of elements of the form
(char function help), each of which defines one additional answer. In this element, char is a character (the answer); function is a function of one argument (an object from list); help is a string.When the user responds with char,
map-y-or-n-pcalls function. If it returns non-nil, the object is considered “acted upon”, andmap-y-or-n-padvances to the next object in list. If it returnsnil, the prompt is repeated for the same object.Normally,
map-y-or-n-pbindscursor-in-echo-areawhile prompting. But if no-cursor-in-echo-area is non-nil, it does not do that.If
map-y-or-n-pis called in a command that was invoked using the mouse—more precisely, iflast-nonmenu-event(see Command Loop Info) is eithernilor a list—then it uses a dialog box or pop-up menu to ask the question. In this case, it does not use keyboard input or the echo area. You can force use of the mouse or use of keyboard input by bindinglast-nonmenu-eventto a suitable value around the call.The return value of
map-y-or-n-pis the number of objects acted on.
To read a password to pass to another program, you can use the
function read-passwd.
This function reads a password, prompting with prompt. It does not echo the password as the user types it; instead, it echoes ‘.’ for each character in the password.
The optional argument confirm, if non-
nil, says to read the password twice and insist it must be the same both times. If it isn't the same, the user has to type it over and over until the last two times match.The optional argument default specifies the default password to return if the user enters empty input. If default is
nil, thenread-passwdreturns the null string in that case.
This section describes some basic functions and variables related to minibuffers.
This command exits the active minibuffer. It is normally bound to keys in minibuffer local keymaps.
This command exits the active minibuffer after inserting the last character typed on the keyboard (found in
last-command-char; see Command Loop Info).
This command replaces the minibuffer contents with the value of the nth previous (older) history element.
This command replaces the minibuffer contents with the value of the nth more recent history element.
This command replaces the minibuffer contents with the value of the nth previous (older) history element that matches pattern (a regular expression).
This command replaces the minibuffer contents with the value of the nth next (newer) history element that matches pattern (a regular expression).
This function returns the prompt string of the currently active minibuffer. If no minibuffer is active, it returns
nil.
This function, available starting in Emacs 21, returns the current position of the end of the minibuffer prompt, if a minibuffer is current. Otherwise, it returns the minimum valid buffer position.
This function, available starting in Emacs 21, returns the editable contents of the minibuffer (that is, everything except the prompt) as a string, if a minibuffer is current. Otherwise, it returns the entire contents of the current buffer.
This is like
minibuffer-contents, except that it does not copy text properties, just the characters themselves. See Text Properties.
This function, available starting in Emacs 21, erases the editable contents of the minibuffer (that is, everything except the prompt), if a minibuffer is current. Otherwise, it erases the entire buffer.
This function returns the current display-width of the minibuffer prompt, if a minibuffer is current. Otherwise, it returns zero.
This is a normal hook that is run whenever the minibuffer is entered. See Hooks.
This is a normal hook that is run whenever the minibuffer is exited. See Hooks.
The current value of this variable is used to rebind
help-formlocally inside the minibuffer (see Help Functions).
This function returns the currently active minibuffer window, or
nilif none is currently active.
This function returns the minibuffer window used for frame frame. If frame is
nil, that stands for the current frame. Note that the minibuffer window used by a frame need not be part of that frame—a frame that has no minibuffer of its own necessarily uses some other frame's minibuffer window.
This function returns non-
nilif window is a minibuffer window.
It is not correct to determine whether a given window is a minibuffer by
comparing it with the result of (minibuffer-window), because
there can be more than one minibuffer window if there is more than one
frame.
This function returns non-
nilif window, assumed to be a minibuffer window, is currently active.
If the value of this variable is non-
nil, it should be a window object. When the functionscroll-other-windowis called in the minibuffer, it scrolls this window.
Finally, some functions and variables deal with recursive minibuffers (see Recursive Editing):
This function returns the current depth of activations of the minibuffer, a nonnegative integer. If no minibuffers are active, it returns zero.
If this variable is non-
nil, you can invoke commands (such asfind-file) that use minibuffers even while the minibuffer window is active. Such invocation produces a recursive editing level for a new minibuffer. The outer-level minibuffer is invisible while you are editing the inner one.If this variable is
nil, you cannot invoke minibuffer commands when the minibuffer window is active, not even if you switch to another window to do it.
If a command name has a property enable-recursive-minibuffers
that is non-nil, then the command can use the minibuffer to read
arguments even if it is invoked from the minibuffer. The minibuffer
command next-matching-history-element (normally M-s in the
minibuffer) uses this feature.
When you run Emacs, it enters the editor command loop almost immediately. This loop reads key sequences, executes their definitions, and displays the results. In this chapter, we describe how these things are done, and the subroutines that allow Lisp programs to do them.
The first thing the command loop must do is read a key sequence, which
is a sequence of events that translates into a command. It does this by
calling the function read-key-sequence. Your Lisp code can also
call this function (see Key Sequence Input). Lisp programs can also
do input at a lower level with read-event (see Reading One Event) or discard pending input with discard-input
(see Event Input Misc).
The key sequence is translated into a command through the currently
active keymaps. See Key Lookup, for information on how this is done.
The result should be a keyboard macro or an interactively callable
function. If the key is M-x, then it reads the name of another
command, which it then calls. This is done by the command
execute-extended-command (see Interactive Call).
To execute a command requires first reading the arguments for it.
This is done by calling command-execute (see Interactive Call). For commands written in Lisp, the interactive
specification says how to read the arguments. This may use the prefix
argument (see Prefix Command Arguments) or may read with prompting
in the minibuffer (see Minibuffers). For example, the command
find-file has an interactive specification which says to
read a file name using the minibuffer. The command's function body does
not use the minibuffer; if you call this command from Lisp code as a
function, you must supply the file name string as an ordinary Lisp
function argument.
If the command is a string or vector (i.e., a keyboard macro) then
execute-kbd-macro is used to execute it. You can call this
function yourself (see Keyboard Macros).
To terminate the execution of a running command, type C-g. This character causes quitting (see Quitting).
The editor command loop runs this normal hook before each command. At that time,
this-commandcontains the command that is about to run, andlast-commanddescribes the previous command. See Hooks.
The editor command loop runs this normal hook after each command (including commands terminated prematurely by quitting or by errors), and also when the command loop is first entered. At that time,
this-commanddescribes the command that just ran, andlast-commanddescribes the command before that. See Hooks.
Quitting is suppressed while running pre-command-hook and
post-command-hook. If an error happens while executing one of
these hooks, it terminates execution of the hook, and clears the hook
variable to nil so as to prevent an infinite loop of errors.
A Lisp function becomes a command when its body contains, at top
level, a form that calls the special form interactive. This
form does nothing when actually executed, but its presence serves as a
flag to indicate that interactive calling is permitted. Its argument
controls the reading of arguments for an interactive call.
interactiveThis section describes how to write the interactive form that
makes a Lisp function an interactively-callable command, and how to
examine a commands's interactive form.
This special form declares that the function in which it appears is a command, and that it may therefore be called interactively (via M-x or by entering a key sequence bound to it). The argument arg-descriptor declares how to compute the arguments to the command when the command is called interactively.
A command may be called from Lisp programs like any other function, but then the caller supplies the arguments and arg-descriptor has no effect.
The
interactiveform has its effect because the command loop (actually, its subroutinecall-interactively) scans through the function definition looking for it, before calling the function. Once the function is called, all its body forms including theinteractiveform are executed, but at this timeinteractivesimply returnsnilwithout even evaluating its argument.
There are three possibilities for the argument arg-descriptor:
nil; then the command is called with no
arguments. This leads quickly to an error if the command requires one
or more arguments.
Here's an example of what not to do:
(interactive
(list (region-beginning) (region-end)
(read-string "Foo: " nil 'my-history)))
Here's how to avoid the problem, by examining point and the mark only after reading the keyboard input:
(interactive
(let ((string (read-string "Foo: " nil 'my-history)))
(list (region-beginning) (region-end) string)))
(interactive "bFrobnicate buffer: ")
The code letter ‘b’ says to read the name of an existing buffer, with completion. The buffer name is the sole argument passed to the command. The rest of the string is a prompt.
If there is a newline character in the string, it terminates the prompt. If the string does not end there, then the rest of the string should contain another code character and prompt, specifying another argument. You can specify any number of arguments in this way.
The prompt string can use ‘%’ to include previous argument values
(starting with the first argument) in the prompt. This is done using
format (see Formatting Strings). For example, here is how
you could read the name of an existing buffer followed by a new name to
give to that buffer:
(interactive "bBuffer to rename: \nsRename buffer %s to: ")
If the first character in the string is ‘*’, then an error is signaled if the buffer is read-only.
If the first character in the string is ‘@’, and if the key sequence used to invoke the command includes any mouse events, then the window associated with the first of those events is selected before the command is run.
You can use ‘*’ and ‘@’ together; the order does not matter. Actual reading of arguments is controlled by the rest of the prompt string (starting with the first character that is not ‘*’ or ‘@’).
This function returns the
interactiveform of function. If function is a command (see Interactive Call), the value is a list of the form(interactivespec), where spec is the descriptor specification used by the command'sinteractiveform to compute the function's arguments (see Using Interactive). If function is not a command,interactive-formreturnsnil.
interactiveThe code character descriptions below contain a number of key words, defined here as follows:
completing-read
(see Completion). ? displays a list of possible completions.
Even though the code letter doesn't use a prompt string, you must follow
it with a newline if it is not the last code character in the string.
Here are the code character descriptions for use with interactive:
fboundp). Existing,
Completion, Prompt.
commandp). Existing,
Completion, Prompt.
default-directory (see System Environment).
Existing, Completion, Default, Prompt.
You can use ‘e’ more than once in a single command's interactive
specification. If the key sequence that invoked the command has
n events that are lists, the nth ‘e’ provides the
nth such event. Events that are not lists, such as function keys
and ascii characters, do not count where ‘e’ is concerned.
default-directory. Existing, Completion, Default,
Prompt.
nil as
the argument's value. No I/O.
This kind of input is used by commands such as describe-key and
global-set-key.
user-variable-p). See High-Level Completion. Existing,
Completion, Prompt.
nil. See Coding Systems. Completion,
Existing, Prompt.
nil as the
argument value. Completion, Existing, Prompt.
interactive
Here are some examples of interactive:
(defun foo1 () ;foo1takes no arguments, (interactive) ; just moves forward two words. (forward-word 2)) => foo1 (defun foo2 (n) ;foo2takes one argument, (interactive "p") ; which is the numeric prefix. (forward-word (* 2 n))) => foo2 (defun foo3 (n) ;foo3takes one argument, (interactive "nCount:") ; which is read with the Minibuffer. (forward-word (* 2 n))) => foo3 (defun three-b (b1 b2 b3) "Select three existing buffers. Put them into three windows, selecting the last one." (interactive "bBuffer1:\nbBuffer2:\nbBuffer3:") (delete-other-windows) (split-window (selected-window) 8) (switch-to-buffer b1) (other-window 1) (split-window (selected-window) 8) (switch-to-buffer b2) (other-window 1) (switch-to-buffer b3)) => three-b (three-b "*scratch*" "declarations.texi" "*mail*") => nil
After the command loop has translated a key sequence into a command it
invokes that command using the function command-execute. If the
command is a function, command-execute calls
call-interactively, which reads the arguments and calls the
command. You can also call these functions yourself.
Returns
tif object is suitable for calling interactively; that is, if object is a command. Otherwise, returnsnil.The interactively callable objects include strings and vectors (treated as keyboard macros), lambda expressions that contain a top-level call to
interactive, byte-code function objects made from such lambda expressions, autoload objects that are declared as interactive (non-nilfourth argument toautoload), and some of the primitive functions.A symbol satisfies
commandpif its function definition satisfiescommandp.Keys and keymaps are not commands. Rather, they are used to look up commands (see Keymaps).
See
documentationin Accessing Documentation, for a realistic example of usingcommandp.
This function calls the interactively callable function command, reading arguments according to its interactive calling specifications. An error is signaled if command is not a function or if it cannot be called interactively (i.e., is not a command). Note that keyboard macros (strings and vectors) are not accepted, even though they are considered commands, because they are not functions.
If record-flag is non-
nil, then this command and its arguments are unconditionally added to the listcommand-history. Otherwise, the command is added only if it uses the minibuffer to read an argument. See Command History.The argument keys, if given, specifies the sequence of events to supply if the command inquires which events were used to invoke it.
This function executes command. The argument command must satisfy the
commandppredicate; i.e., it must be an interactively callable function or a keyboard macro.A string or vector as command is executed with
execute-kbd-macro. A function is passed tocall-interactively, along with the optional record-flag.A symbol is handled by using its function definition in its place. A symbol with an
autoloaddefinition counts as a command if it was declared to stand for an interactively callable function. Such a definition is handled by loading the specified library and then rechecking the definition of the symbol.The argument keys, if given, specifies the sequence of events to supply if the command inquires which events were used to invoke it.
The argument special, if given, means to ignore the prefix argument and not clear it. This is used for executing special events (see Special Events).
This function reads a command name from the minibuffer using
completing-read(see Completion). Then it usescommand-executeto call the specified command. Whatever that command returns becomes the value ofexecute-extended-command.If the command asks for a prefix argument, it receives the value prefix-argument. If
execute-extended-commandis called interactively, the current raw prefix argument is used for prefix-argument, and thus passed on to whatever command is run.
execute-extended-commandis the normal definition of M-x, so it uses the string ‘M-x ’ as a prompt. (It would be better to take the prompt from the events used to invokeexecute-extended-command, but that is painful to implement.) A description of the value of the prefix argument, if any, also becomes part of the prompt.(execute-extended-command 1) ---------- Buffer: Minibuffer ---------- 1 M-x forward-word RET ---------- Buffer: Minibuffer ---------- => t
This function returns
tif the containing function (the one whose code includes the call tointeractive-p) was called interactively, with the functioncall-interactively. (It makes no difference whethercall-interactivelywas called from Lisp or directly from the editor command loop.) If the containing function was called by Lisp evaluation (or withapplyorfuncall), then it was not called interactively.
The most common use of interactive-p is for deciding whether to
print an informative message. As a special exception,
interactive-p returns nil whenever a keyboard macro is
being run. This is to suppress the informative messages and speed
execution of the macro.
For example:
(defun foo ()
(interactive)
(when (interactive-p)
(message "foo")))
=> foo
(defun bar ()
(interactive)
(setq foobar (list (foo) (interactive-p))))
=> bar
;; Type M-x foo.
-| foo
;; Type M-x bar.
;; This does not print anything.
foobar
=> (nil t)
The other way to do this sort of job is to make the command take an
argument print-message which should be non-nil in an
interactive call, and use the interactive spec to make sure it is
non-nil. Here's how:
(defun foo (&optional print-message)
(interactive "p")
(when print-message
(message "foo")))
The numeric prefix argument, provided by ‘p’, is never nil.
The editor command loop sets several Lisp variables to keep status records for itself and for commands that are run.
This variable records the name of the previous command executed by the command loop (the one before the current command). Normally the value is a symbol with a function definition, but this is not guaranteed.
The value is copied from
this-commandwhen a command returns to the command loop, except when the command has specified a prefix argument for the following command.This variable is always local to the current terminal and cannot be buffer-local. See Multiple Displays.
This variable is set up by Emacs just like
last-command, but never altered by Lisp programs.
This variable records the name of the command now being executed by the editor command loop. Like
last-command, it is normally a symbol with a function definition.The command loop sets this variable just before running a command, and copies its value into
last-commandwhen the command finishes (unless the command specified a prefix argument for the following command).Some commands set this variable during their execution, as a flag for whatever command runs next. In particular, the functions for killing text set
this-commandtokill-regionso that any kill commands immediately following will know to append the killed text to the previous kill.
If you do not want a particular command to be recognized as the previous
command in the case where it got an error, you must code that command to
prevent this. One way is to set this-command to t at the
beginning of the command, and set this-command back to its proper
value at the end, like this:
(defun foo (args...)
(interactive ...)
(let ((old-this-command this-command))
(setq this-command t)
...do the work...
(setq this-command old-this-command)))
We do not bind this-command with let because that would
restore the old value in case of error—a feature of let which
in this case does precisely what we want to avoid.
This function returns a string or vector containing the key sequence that invoked the present command, plus any previous commands that generated the prefix argument for this command. The value is a string if all those events were characters. See Input Events.
(this-command-keys) ;; Now use C-u C-x C-e to evaluate that. => "^U^X^E"
Like
this-command-keys, except that it always returns the events in a vector, so you don't need to deal with the complexities of storing input events in a string (see Strings of Events).
This function empties out the table of events for
this-command-keysto return, and also empties the records that the functionrecent-keys(see Recording Input) will subsequently return. This is useful after reading a password, to prevent the password from echoing inadvertently as part of the next command in certain cases.
This variable holds the last input event read as part of a key sequence, not counting events resulting from mouse menus.
One use of this variable is for telling
x-popup-menuwhere to pop up a menu. It is also used internally byy-or-n-p(see Yes-or-No Queries).
This variable is set to the last input event that was read by the command loop as part of a command. The principal use of this variable is in
self-insert-command, which uses it to decide which character to insert.last-command-event ;; Now use C-u C-x C-e to evaluate that. => 5The value is 5 because that is the ascii code for C-e.
The alias
last-command-charexists for compatibility with Emacs version 18.
This variable records which frame the last input event was directed to. Usually this is the frame that was selected when the event was generated, but if that frame has redirected input focus to another frame, the value is the frame to which the event was redirected. See Input Focus.
It is not easy to display a value of point in the middle of a sequence
of text that has the display or composition property. So
after a command finishes and returns to the command loop, if point is
within such a sequence, the command loop normally moves point to the
edge of the sequence.
A command can inhibit this feature by setting the variable
disable-point-adjustment:
If this variable is non-
nilwhen a command returns to the command loop, then the command loop does not check for text properties such asdisplayandcomposition, and does not move point out of sequences that have these properties.The command loop sets this variable to
nilbefore each command, so if a command sets it, the effect applies only to that command.
If you set this variable to a non-
nilvalue, the feature of moving point out of these sequences is completely turned off.
The Emacs command loop reads a sequence of input events that represent keyboard or mouse activity. The events for keyboard activity are characters or symbols; mouse events are always lists. This section describes the representation and meaning of input events in detail.
This function returns non-
nilif object is an input event or event type.Note that any symbol might be used as an event or an event type.
eventpcannot distinguish whether a symbol is intended by Lisp code to be used as an event. Instead, it distinguishes whether the symbol has actually been used in an event that has been read as input in the current Emacs session. If a symbol has not yet been so used,eventpreturnsnil.
There are two kinds of input you can get from the keyboard: ordinary keys, and function keys. Ordinary keys correspond to characters; the events they generate are represented in Lisp as characters. The event type of a character event is the character itself (an integer); see Classifying Events.
An input character event consists of a basic code between 0 and 524287, plus any or all of these modifier bits:
ascii control characters such as C-a have special basic codes of their own, so Emacs needs no special bit to indicate them. Thus, the code for C-a is just 1.
But if you type a control combination not in ascii, such as
% with the control key, the numeric value you get is the code
for % plus
2**26
(assuming the terminal supports non-ascii
control characters).
For letters, the basic code itself indicates upper versus lower case; for digits and punctuation, the shift key selects an entirely different character with a different basic code. In order to keep within the ascii character set whenever possible, Emacs avoids using the 2**25 bit for those characters.
However, ascii provides no way to distinguish C-A from
C-a, so Emacs uses the
2**25
bit in C-A and not in
C-a.
It is best to avoid mentioning specific bit numbers in your program.
To test the modifier bits of a character, use the function
event-modifiers (see Classifying Events). When making key
bindings, you can use the read syntax for characters with modifier bits
(‘\C-’, ‘\M-’, and so on). For making key bindings with
define-key, you can use lists such as (control hyper ?x) to
specify the characters (see Changing Key Bindings). The function
event-convert-list converts such a list into an event type
(see Classifying Events).
Most keyboards also have function keys—keys that have names or
symbols that are not characters. Function keys are represented in Emacs
Lisp as symbols; the symbol's name is the function key's label, in lower
case. For example, pressing a key labeled <F1> places the symbol
f1 in the input stream.
The event type of a function key event is the event symbol itself. See Classifying Events.
Here are a few special cases in the symbol-naming convention for function keys:
backspace, tab, newline, return, deleteIn ascii, C-i and <TAB> are the same character. If the
terminal can distinguish between them, Emacs conveys the distinction to
Lisp programs by representing the former as the integer 9, and the
latter as the symbol tab.
Most of the time, it's not useful to distinguish the two. So normally
function-key-map (see Translating Input) is set up to map
tab into 9. Thus, a key binding for character code 9 (the
character C-i) also applies to tab. Likewise for the other
symbols in this group. The function read-char likewise converts
these events into characters.
In ascii, <BS> is really C-h. But backspace
converts into the character code 127 (<DEL>), not into code 8
(<BS>). This is what most users prefer.
left, up, right, downkp-add, kp-decimal, kp-divide, ...kp-0, kp-1, ...kp-f1, kp-f2, kp-f3, kp-f4kp-home, kp-left, kp-up, kp-right, kp-downhome, left, ...
kp-prior, kp-next, kp-end, kp-begin, kp-insert, kp-deleteYou can use the modifier keys <ALT>, <CTRL>, <HYPER>, <META>, <SHIFT>, and <SUPER> with function keys. The way to represent them is with prefixes in the symbol name:
Thus, the symbol for the key <F3> with <META> held down is
M-f3. When you use more than one prefix, we recommend you
write them in alphabetical order; but the order does not matter in
arguments to the key-binding lookup and modification functions.
Emacs supports four kinds of mouse events: click events, drag events, button-down events, and motion events. All mouse events are represented as lists. The car of the list is the event type; this says which mouse button was involved, and which modifier keys were used with it. The event type can also distinguish double or triple button presses (see Repeat Events). The rest of the list elements give position and time information.
For key lookup, only the event type matters: two events of the same type necessarily run the same command. The command can access the full values of these events using the ‘e’ interactive code. See Interactive Codes.
A key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer. This does not imply that clicking in a window selects that window or its buffer—that is entirely under the control of the command binding of the key sequence.
When the user presses a mouse button and releases it at the same location, that generates a click event. Mouse click events have this form:
(event-type
(window buffer-pos (x . y) timestamp)
click-count)
Here is what the elements normally mean:
mouse-1, mouse-2, ..., where the
buttons are numbered left to right.
You can also use prefixes ‘A-’, ‘C-’, ‘H-’, ‘M-’, ‘S-’ and ‘s-’ for modifiers alt, control, hyper, meta, shift and super, just as you would with function keys.
This symbol also serves as the event type of the event. Key bindings
describe events by their types; thus, if there is a key binding for
mouse-1, that binding would apply to all events whose
event-type is mouse-1.
(0 . 0).
The meanings of buffer-pos, x and y are somewhat different when the event location is in a special part of the screen, such as the mode line or a scroll bar.
If the location is in a scroll bar, then buffer-pos is the symbol
vertical-scroll-bar or horizontal-scroll-bar, and the pair
(x . y) is replaced with a pair (portion
. whole), where portion is the distance of the click from
the top or left end of the scroll bar, and whole is the length of
the entire scroll bar.
If the position is on a mode line or the vertical line separating
window from its neighbor to the right, then buffer-pos is
the symbol mode-line, header-line, or
vertical-line. For the mode line, y does not have
meaningful data. For the vertical line, x does not have
meaningful data.
In one special case, buffer-pos is a list containing a symbol (one of the symbols listed above) instead of just the symbol. This happens after the imaginary prefix keys for the event are inserted into the input stream. See Key Sequence Input.
With Emacs, you can have a drag event without even changing your clothes. A drag event happens every time the user presses a mouse button and then moves the mouse to a different character position before releasing the button. Like all mouse events, drag events are represented in Lisp as lists. The lists record both the starting mouse position and the final position, like this:
(event-type
(window1 buffer-pos1 (x1 . y1) timestamp1)
(window2 buffer-pos2 (x2 . y2) timestamp2)
click-count)
For a drag event, the name of the symbol event-type contains the
prefix ‘drag-’. For example, dragging the mouse with button 2 held
down generates a drag-mouse-2 event. The second and third
elements of the event give the starting and ending position of the drag.
Aside from that, the data have the same meanings as in a click event
(see Click Events). You can access the second element of any mouse
event in the same way, with no need to distinguish drag events from
others.
The ‘drag-’ prefix follows the modifier key prefixes such as ‘C-’ and ‘M-’.
If read-key-sequence receives a drag event that has no key
binding, and the corresponding click event does have a binding, it
changes the drag event into a click event at the drag's starting
position. This means that you don't have to distinguish between click
and drag events unless you want to.
Click and drag events happen when the user releases a mouse button. They cannot happen earlier, because there is no way to distinguish a click from a drag until the button is released.
If you want to take action as soon as a button is pressed, you need to handle button-down events.5 These occur as soon as a button is pressed. They are represented by lists that look exactly like click events (see Click Events), except that the event-type symbol name contains the prefix ‘down-’. The ‘down-’ prefix follows modifier key prefixes such as ‘C-’ and ‘M-’.
The function read-key-sequence ignores any button-down events
that don't have command bindings; therefore, the Emacs command loop
ignores them too. This means that you need not worry about defining
button-down events unless you want them to do something. The usual
reason to define a button-down event is so that you can track mouse
motion (by reading motion events) until the button is released.
See Motion Events.
If you press the same mouse button more than once in quick succession without moving the mouse, Emacs generates special repeat mouse events for the second and subsequent presses.
The most common repeat events are double-click events. Emacs generates a double-click event when you click a button twice; the event happens when you release the button (as is normal for all click events).
The event type of a double-click event contains the prefix
‘double-’. Thus, a double click on the second mouse button with
<meta> held down comes to the Lisp program as
M-double-mouse-2. If a double-click event has no binding, the
binding of the corresponding ordinary click event is used to execute
it. Thus, you need not pay attention to the double click feature
unless you really want to.
When the user performs a double click, Emacs generates first an ordinary click event, and then a double-click event. Therefore, you must design the command binding of the double click event to assume that the single-click command has already run. It must produce the desired results of a double click, starting from the results of a single click.
This is convenient, if the meaning of a double click somehow “builds on” the meaning of a single click—which is recommended user interface design practice for double clicks.
If you click a button, then press it down again and start moving the mouse with the button held down, then you get a double-drag event when you ultimately release the button. Its event type contains ‘double-drag’ instead of just ‘drag’. If a double-drag event has no binding, Emacs looks for an alternate binding as if the event were an ordinary drag.
Before the double-click or double-drag event, Emacs generates a double-down event when the user presses the button down for the second time. Its event type contains ‘double-down’ instead of just ‘down’. If a double-down event has no binding, Emacs looks for an alternate binding as if the event were an ordinary button-down event. If it finds no binding that way either, the double-down event is ignored.
To summarize, when you click a button and then press it again right away, Emacs generates a down event and a click event for the first click, a double-down event when you press the button again, and finally either a double-click or a double-drag event.
If you click a button twice and then press it again, all in quick succession, Emacs generates a triple-down event, followed by either a triple-click or a triple-drag. The event types of these events contain ‘triple’ instead of ‘double’. If any triple event has no binding, Emacs uses the binding that it would use for the corresponding double event.
If you click a button three or more times and then press it again, the events for the presses beyond the third are all triple events. Emacs does not have separate event types for quadruple, quintuple, etc. events. However, you can look at the event list to find out precisely how many times the button was pressed.
This function returns the number of consecutive button presses that led up to event. If event is a double-down, double-click or double-drag event, the value is 2. If event is a triple event, the value is 3 or greater. If event is an ordinary mouse event (not a repeat event), the value is 1.
To generate repeat events, successive mouse button presses must be at approximately the same screen position. The value of
double-click-fuzzspecifies the maximum number of pixels the mouse may be moved between two successive clicks to make a double-click.
To generate repeat events, the number of milliseconds between successive button presses must be less than the value of
double-click-time. Settingdouble-click-timetonildisables multi-click detection entirely. Setting it totremoves the time limit; Emacs then detects multi-clicks by position only.
Emacs sometimes generates mouse motion events to describe motion of the mouse without any button activity. Mouse motion events are represented by lists that look like this:
(mouse-movement (window buffer-pos (x . y) timestamp))
The second element of the list describes the current position of the mouse, just as in a click event (see Click Events).
The special form track-mouse enables generation of motion events
within its body. Outside of track-mouse forms, Emacs does not
generate events for mere motion of the mouse, and these events do not
appear. See Mouse Tracking.
Window systems provide general ways for the user to control which window gets keyboard input. This choice of window is called the focus. When the user does something to switch between Emacs frames, that generates a focus event. The normal definition of a focus event, in the global keymap, is to select a new frame within Emacs, as the user would expect. See Input Focus.
Focus events are represented in Lisp as lists that look like this:
(switch-frame new-frame)
where new-frame is the frame switched to.
Most X window managers are set up so that just moving the mouse into a window is enough to set the focus there. Emacs appears to do this, because it changes the cursor to solid in the new frame. However, there is no need for the Lisp program to know about the focus change until some other kind of input arrives. So Emacs generates a focus event only when the user actually types a keyboard key or presses a mouse button in the new frame; just moving the mouse between frames does not generate a focus event.
A focus event in the middle of a key sequence would garble the sequence. So Emacs never generates a focus event in the middle of a key sequence. If the user changes focus in the middle of a key sequence—that is, after a prefix key—then Emacs reorders the events so that the focus event comes either before or after the multi-event key sequence, and not within it.
A few other event types represent occurrences within the window system.
(delete-frame (frame))The standard definition of the delete-frame event is to delete frame.
(iconify-frame (frame))ignore; since the
frame has already been iconified, Emacs has no work to do. The purpose
of this event type is so that you can keep track of such events if you
want to.
(make-frame-visible (frame))ignore; since the
frame has already been made visible, Emacs has no work to do.
(mouse-wheel position delta)The element delta describes the amount and direction of the wheel rotation. Its absolute value is the number of increments by which the wheel was rotated. A negative delta indicates that the wheel was rotated backwards, towards the user, and a positive delta indicates that the wheel was rotated forward, away from the user.
The element position is a list describing the position of the event, in the same format as used in a mouse-click event.
This kind of event is generated only on some kinds of systems.
(drag-n-drop position files)The element position is a list describing the position of the event, in the same format as used in a mouse-click event, and files is the list of file names that were dragged and dropped. The usual way to handle this event is by visiting these files.
This kind of event is generated, at present, only on some kinds of systems.
If one of these events arrives in the middle of a key sequence—that is, after a prefix key—then Emacs reorders the events so that this event comes either before or after the multi-event key sequence, not within it.
If the user presses and releases the left mouse button over the same location, that generates a sequence of events like this:
(down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320))
(mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864180))
While holding the control key down, the user might hold down the second mouse button, and drag the mouse from one line to the next. That produces two events, as shown here:
(C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
(C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
(#<window 18 on NEWS> 3510 (0 . 28) -729648))
While holding down the meta and shift keys, the user might press the second mouse button on the window's mode line, and then drag the mouse into another window. That produces a pair of events like these:
(M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
(M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
(#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
-453816))
Every event has an event type, which classifies the event for key binding purposes. For a keyboard event, the event type equals the event value; thus, the event type for a character is the character, and the event type for a function key symbol is the symbol itself. For events that are lists, the event type is the symbol in the car of the list. Thus, the event type is always a symbol or a character.
Two events of the same type are equivalent where key bindings are concerned; thus, they always run the same command. That does not necessarily mean they do the same things, however, as some commands look at the whole event to decide what to do. For example, some commands use the location of a mouse event to decide where in the buffer to act.
Sometimes broader classifications of events are useful. For example, you might want to ask whether an event involved the <META> key, regardless of which other key or mouse button was used.
The functions event-modifiers and event-basic-type are
provided to get such information conveniently.
This function returns a list of the modifiers that event has. The modifiers are symbols; they include
shift,control,meta,alt,hyperandsuper. In addition, the modifiers list of a mouse event symbol always contains one ofclick,drag, anddown.The argument event may be an entire event object, or just an event type.
Here are some examples:
(event-modifiers ?a) => nil (event-modifiers ?\C-a) => (control) (event-modifiers ?\C-%) => (control) (event-modifiers ?\C-\S-a) => (control shift) (event-modifiers 'f5) => nil (event-modifiers 's-f5) => (super) (event-modifiers 'M-S-f5) => (meta shift) (event-modifiers 'mouse-1) => (click) (event-modifiers 'down-mouse-1) => (down)The modifiers list for a click event explicitly contains
click, but the event symbol name itself does not contain ‘click’.
This function returns the key or mouse button that event describes, with all modifiers removed. For example:
(event-basic-type ?a) => 97 (event-basic-type ?A) => 97 (event-basic-type ?\C-a) => 97 (event-basic-type ?\C-\S-a) => 97 (event-basic-type 'f5) => f5 (event-basic-type 's-f5) => f5 (event-basic-type 'M-S-f5) => f5 (event-basic-type 'down-mouse-1) => mouse-1
This function returns non-
nilif object is a mouse movement event.
This function converts a list of modifier names and a basic event type to an event type which specifies all of them. For example,
(event-convert-list '(control ?a)) => 1 (event-convert-list '(control meta ?a)) => -134217727 (event-convert-list '(control super f1)) => C-s-f1
This section describes convenient functions for accessing the data in a mouse button or motion event.
These two functions return the starting or ending position of a mouse-button event, as a list of this form:
(window buffer-position (x . y) timestamp)
This returns the starting position of event.
If event is a click or button-down event, this returns the location of the event. If event is a drag event, this returns the drag's starting position.
This returns the ending position of event.
If event is a drag event, this returns the position where the user released the mouse button. If event is a click or button-down event, the value is actually the starting position, which is the only position such events have.
These five functions take a position list as described above, and return various parts of it.
Return the pixel-based x and y coordinates in position, as a cons cell
(x.y).
Return the row and column (in units of characters) of position, as a cons cell
(col.row). These are computed from the x and y values actually found in position.
These functions are useful for decoding scroll bar events.
This function returns the fractional vertical position of a scroll bar event within the scroll bar. The value is a cons cell
(portion.whole)containing two integers whose ratio is the fractional position.
This function multiplies (in effect) ratio by total, rounding the result to an integer. The argument ratio is not a number, but rather a pair
(num.denom)—typically a value returned byscroll-bar-event-ratio.This function is handy for scaling a position on a scroll bar into a buffer position. Here's how to do that:
(+ (point-min) (scroll-bar-scale (posn-x-y (event-start event)) (- (point-max) (point-min))))Recall that scroll bar events have two integers forming a ratio, in place of a pair of x and y coordinates.
In most of the places where strings are used, we conceptualize the string as containing text characters—the same kind of characters found in buffers or files. Occasionally Lisp programs use strings that conceptually contain keyboard characters; for example, they may be key sequences or keyboard macro definitions. However, storing keyboard characters in a string is a complex matter, for reasons of historical compatibility, and it is not always possible.
We recommend that new programs avoid dealing with these complexities by not storing keyboard events in strings. Here is how to do that:
lookup-key and
define-key. For example, you can use
read-key-sequence-vector instead of read-key-sequence, and
this-command-keys-vector instead of this-command-keys.
define-key.
listify-key-sequence (see Event Input Misc)
first, to convert it to a list.
The complexities stem from the modifier bits that keyboard input characters can include. Aside from the Meta modifier, none of these modifier bits can be included in a string, and the Meta modifier is allowed only in special cases.
The earliest GNU Emacs versions represented meta characters as codes
in the range of 128 to 255. At that time, the basic character codes
ranged from 0 to 127, so all keyboard character codes did fit in a
string. Many Lisp programs used ‘\M-’ in string constants to stand
for meta characters, especially in arguments to define-key and
similar functions, and key sequences and sequences of events were always
represented as strings.
When we added support for larger basic character codes beyond 127, and additional modifier bits, we had to change the representation of meta characters. Now the flag that represents the Meta modifier in a character is 2**27 and such numbers cannot be included in a string.
To support programs with ‘\M-’ in string constants, there are special rules for including certain meta characters in a string. Here are the rules for interpreting a string as a sequence of input characters:
Functions such as read-key-sequence that construct strings of
keyboard input characters follow these rules: they construct vectors
instead of strings, when the events won't fit in a string.
When you use the read syntax ‘\M-’ in a string, it produces a code in the range of 128 to 255—the same code that you get if you modify the corresponding keyboard event to put it in the string. Thus, meta events in strings work consistently regardless of how they get into the strings.
However, most programs would do well to avoid these issues by following the recommendations at the beginning of this section.
The editor command loop reads key sequences using the function
read-key-sequence, which uses read-event. These and other
functions for event input are also available for use in Lisp programs.
See also momentary-string-display in Temporary Displays,
and sit-for in Waiting. See Terminal Input, for
functions and variables for controlling terminal input modes and
debugging terminal input. See Translating Input, for features you
can use for translating or modifying input events while reading them.
For higher-level input facilities, see Minibuffers.
The command loop reads input a key sequence at a time, by calling
read-key-sequence. Lisp programs can also call this function;
for example, describe-key uses it to read the key to describe.
This function reads a key sequence and returns it as a string or vector. It keeps reading events until it has accumulated a complete key sequence; that is, enough to specify a non-prefix command using the currently active keymaps.
If the events are all characters and all can fit in a string, then
read-key-sequencereturns a string (see Strings of Events). Otherwise, it returns a vector, since a vector can hold all kinds of events—characters, symbols, and lists. The elements of the string or vector are the events in the key sequence.The argument prompt is either a string to be displayed in the echo area as a prompt, or
nil, meaning not to display a prompt.In the example below, the prompt ‘?’ is displayed in the echo area, and the user types C-x C-f.
(read-key-sequence "?") ---------- Echo Area ---------- ?C-x C-f ---------- Echo Area ---------- => "^X^F"The function
read-key-sequencesuppresses quitting: C-g typed while reading with this function works like any other character, and does not setquit-flag. See Quitting.
This is like
read-key-sequenceexcept that it always returns the key sequence as a vector, never as a string. See Strings of Events.
If an input character is an upper-case letter and has no key binding,
but its lower-case equivalent has one, then read-key-sequence
converts the character to lower case. Note that lookup-key does
not perform case conversion in this way.
The function read-key-sequence also transforms some mouse events.
It converts unbound drag events into click events, and discards unbound
button-down events entirely. It also reshuffles focus events and
miscellaneous window events so that they never appear in a key sequence
with any other events.
When mouse events occur in special parts of a window, such as a mode
line or a scroll bar, the event type shows nothing special—it is the
same symbol that would normally represent that combination of mouse
button and modifier keys. The information about the window part is kept
elsewhere in the event—in the coordinates. But
read-key-sequence translates this information into imaginary
“prefix keys”, all of which are symbols: header-line,
horizontal-scroll-bar, menu-bar, mode-line,
vertical-line, and vertical-scroll-bar. You can define
meanings for mouse clicks in special window parts by defining key
sequences using these imaginary prefix keys.
For example, if you call read-key-sequence and then click the
mouse on the window's mode line, you get two events, like this:
(read-key-sequence "Click on the mode line: ")
=> [mode-line
(mouse-1
(#<window 6 on NEWS> mode-line
(40 . 63) 5959987))]
This variable's value is the number of key sequences processed so far in this Emacs session. This includes key sequences read from the terminal and key sequences read from keyboard macros being executed.
This variable holds the total number of input events received so far from the terminal—not counting those generated by keyboard macros.
The lowest level functions for command input are those that read a single event.
This function reads and returns the next event of command input, waiting if necessary until an event is available. Events can come directly from the user or from a keyboard macro.
If the optional argument prompt is non-
nil, it should be a string to display in the echo area as a prompt. Otherwise,read-eventdoes not display any message to indicate it is waiting for input; instead, it prompts by echoing: it displays descriptions of the events that led to or were read by the current command. See The Echo Area.If inherit-input-method is non-
nil, then the current input method (if any) is employed to make it possible to enter a non-ascii character. Otherwise, input method handling is disabled for reading this event.If
cursor-in-echo-areais non-nil, thenread-eventmoves the cursor temporarily to the echo area, to the end of any message displayed there. Otherwiseread-eventdoes not move the cursor.If
read-eventgets an event that is defined as a help character, in some casesread-eventprocesses the event directly without returning. See Help Functions. Certain other events, called special events, are also processed directly withinread-event(see Special Events).Here is what happens if you call
read-eventand then press the right-arrow function key:(read-event) => right
This function reads and returns a character of command input. If the user generates an event which is not a character (i.e. a mouse click or function key event),
read-charsignals an error. The arguments work as inread-event.In the first example, the user types the character 1 (ascii code 49). The second example shows a keyboard macro definition that calls
read-charfrom the minibuffer usingeval-expression.read-charreads the keyboard macro's very next character, which is 1. Theneval-expressiondisplays its return value in the echo area.(read-char) => 49 ;; We assume here you use M-: to evaluate this. (symbol-function 'foo) => "^[:(read-char)^M1" (execute-kbd-macro 'foo) -| 49 => nil
This function reads and returns a character of command input. If the user generates an event which is not a character,
read-char-exclusiveignores it and reads another event, until it gets a character. The arguments work as inread-event.
The event-reading functions invoke the current input method, if any
(see Input Methods). If the value of input-method-function
is non-nil, it should be a function; when read-event reads
a printing character (including <SPC>) with no modifier bits, it
calls that function, passing the character as an argument.
If this is non-
nil, its value specifies the current input method function.Note: Don't bind this variable with
let. It is often buffer-local, and if you bind it around reading input (which is exactly when you would bind it), switching buffers asynchronously while Emacs is waiting will cause the value to be restored in the wrong buffer.
The input method function should return a list of events which should
be used as input. (If the list is nil, that means there is no
input, so read-event waits for another event.) These events are
processed before the events in unread-command-events
(see Event Input Misc). Events
returned by the input method function are not passed to the input method
function again, even if they are printing characters with no modifier
bits.
If the input method function calls read-event or
read-key-sequence, it should bind input-method-function to
nil first, to prevent recursion.
The input method function is not called when reading the second and
subsequent events of a key sequence. Thus, these characters are not
subject to input method processing. The input method function should
test the values of overriding-local-map and
overriding-terminal-local-map; if either of these variables is
non-nil, the input method should put its argument into a list and
return that list with no further processing.
You can use the function read-quoted-char to ask the user to
specify a character, and allow the user to specify a control or meta
character conveniently, either literally or as an octal character code.
The command quoted-insert uses this function.
This function is like
read-char, except that if the first character read is an octal digit (0-7), it reads any number of octal digits (but stopping if a non-octal digit is found), and returns the character represented by that numeric character code.Quitting is suppressed when the first character is read, so that the user can enter a C-g. See Quitting.
If prompt is supplied, it specifies a string for prompting the user. The prompt string is always displayed in the echo area, followed by a single ‘-’.
In the following example, the user types in the octal number 177 (which is 127 in decimal).
(read-quoted-char "What character") ---------- Echo Area ---------- What character-177 ---------- Echo Area ---------- => 127
This section describes how to “peek ahead” at events without using
them up, how to check for pending input, and how to discard pending
input. See also the function read-passwd (see Reading a Password).
This variable holds a list of events waiting to be read as command input. The events are used in the order they appear in the list, and removed one by one as they are used.
The variable is needed because in some cases a function reads an event and then decides not to use it. Storing the event in this variable causes it to be processed normally, by the command loop or by the functions to read command input.
For example, the function that implements numeric prefix arguments reads any number of digits. When it finds a non-digit event, it must unread the event so that it can be read normally by the command loop. Likewise, incremental search uses this feature to unread events with no special meaning in a search, because these events should exit the search and then execute normally.
The reliable and easy way to extract events from a key sequence so as to put them in
unread-command-eventsis to uselistify-key-sequence(see Strings of Events).Normally you add events to the front of this list, so that the events most recently unread will be reread first.
This function converts the string or vector key to a list of individual events, which you can put in
unread-command-events.
This variable holds a character to be read as command input. A value of -1 means “empty”.
This variable is mostly obsolete now that you can use
unread-command-eventsinstead; it exists only to support programs written for Emacs versions 18 and earlier.
This function determines whether any command input is currently available to be read. It returns immediately, with value
tif there is available input,nilotherwise. On rare occasions it may returntwhen no input is available.
This variable records the last terminal input event read, whether as part of a command or explicitly by a Lisp program.
In the example below, the Lisp program reads the character 1, ascii code 49. It becomes the value of
last-input-event, while C-e (we assume C-x C-e command is used to evaluate this expression) remains the value oflast-command-event.(progn (print (read-char)) (print last-command-event) last-input-event) -| 49 -| 5 => 49The alias
last-input-charexists for compatibility with Emacs version 18.
This function discards the contents of the terminal input buffer and cancels any keyboard macro that might be in the process of definition. It returns
nil.In the following example, the user may type a number of characters right after starting the evaluation of the form. After the
sleep-forfinishes sleeping,discard-inputdiscards any characters typed during the sleep.(progn (sleep-for 2) (discard-input)) => nil
Special events are handled at a very low level—as soon as they are
read. The read-event function processes these events itself, and
never returns them.
Events that are handled in this way do not echo, they are never grouped
into key sequences, and they never appear in the value of
last-command-event or (this-command-keys). They do not
discard a numeric argument, they cannot be unread with
unread-command-events, they may not appear in a keyboard macro,
and they are not recorded in a keyboard macro while you are defining
one.
These events do, however, appear in last-input-event immediately
after they are read, and this is the way for the event's definition to
find the actual event.
The events types iconify-frame, make-frame-visible and
delete-frame are normally handled in this way. The keymap which
defines how to handle special events—and which events are special—is
in the variable special-event-map (see Active Keymaps).
The wait functions are designed to wait for a certain amount of time
to pass or until there is input. For example, you may wish to pause in
the middle of a computation to allow the user time to view the display.
sit-for pauses and updates the screen, and returns immediately if
input comes in, while sleep-for pauses without updating the
screen.
This function performs redisplay (provided there is no pending input from the user), then waits seconds seconds, or until input is available. The value is
tifsit-forwaited the full time with no input arriving (seeinput-pending-pin Event Input Misc). Otherwise, the value isnil.The argument seconds need not be an integer. If it is a floating point number,
sit-forwaits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down.The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. If the system doesn't support waiting fractions of a second, you get an error if you specify nonzero millisec.
The expression
(sit-for 0)is a convenient way to request a redisplay, without any delay. See Forcing Redisplay.If nodisp is non-
nil, thensit-fordoes not redisplay, but it still returns as soon as input is available (or when the timeout elapses).Iconifying or deiconifying a frame makes
sit-forreturn, because that generates an event. See Misc Events.The usual purpose of
sit-foris to give the user time to read text that you display.
This function simply pauses for seconds seconds without updating the display. It pays no attention to available input. It returns
nil.The argument seconds need not be an integer. If it is a floating point number,
sleep-forwaits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down.The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. If the system doesn't support waiting fractions of a second, you get an error if you specify nonzero millisec.
Use
sleep-forwhen you wish to guarantee a delay.
See Time of Day, for functions to get the current time.
Typing C-g while a Lisp function is running causes Emacs to quit whatever it is doing. This means that control returns to the innermost active command loop.
Typing C-g while the command loop is waiting for keyboard input
does not cause a quit; it acts as an ordinary input character. In the
simplest case, you cannot tell the difference, because C-g
normally runs the command keyboard-quit, whose effect is to quit.
However, when C-g follows a prefix key, they combine to form an
undefined key. The effect is to cancel the prefix key as well as any
prefix argument.
In the minibuffer, C-g has a different definition: it aborts out of the minibuffer. This means, in effect, that it exits the minibuffer and then quits. (Simply quitting would return to the command loop within the minibuffer.) The reason why C-g does not quit directly when the command reader is reading input is so that its meaning can be redefined in the minibuffer in this way. C-g following a prefix key is not redefined in the minibuffer, and it has its normal effect of canceling the prefix key and prefix argument. This too would not be possible if C-g always quit directly.
When C-g does directly quit, it does so by setting the variable
quit-flag to t. Emacs checks this variable at appropriate
times and quits if it is not nil. Setting quit-flag
non-nil in any way thus causes a quit.
At the level of C code, quitting cannot happen just anywhere; only at the
special places that check quit-flag. The reason for this is
that quitting at other places might leave an inconsistency in Emacs's
internal state. Because quitting is delayed until a safe place, quitting
cannot make Emacs crash.
Certain functions such as read-key-sequence or
read-quoted-char prevent quitting entirely even though they wait
for input. Instead of quitting, C-g serves as the requested
input. In the case of read-key-sequence, this serves to bring
about the special behavior of C-g in the command loop. In the
case of read-quoted-char, this is so that C-q can be used
to quote a C-g.
You can prevent quitting for a portion of a Lisp function by binding
the variable inhibit-quit to a non-nil value. Then,
although C-g still sets quit-flag to t as usual, the
usual result of this—a quit—is prevented. Eventually,
inhibit-quit will become nil again, such as when its
binding is unwound at the end of a let form. At that time, if
quit-flag is still non-nil, the requested quit happens
immediately. This behavior is ideal when you wish to make sure that
quitting does not happen within a “critical section” of the program.
In some functions (such as read-quoted-char), C-g is
handled in a special way that does not involve quitting. This is done
by reading the input with inhibit-quit bound to t, and
setting quit-flag to nil before inhibit-quit
becomes nil again. This excerpt from the definition of
read-quoted-char shows how this is done; it also shows that
normal quitting is permitted after the first character of input.
(defun read-quoted-char (&optional prompt)
"...documentation..."
(let ((message-log-max nil) done (first t) (code 0) char)
(while (not done)
(let ((inhibit-quit first)
...)
(and prompt (message "%s-" prompt))
(setq char (read-event))
(if inhibit-quit (setq quit-flag nil)))
...set the variable code...)
code))
If this variable is non-
nil, then Emacs quits immediately, unlessinhibit-quitis non-nil. Typing C-g ordinarily setsquit-flagnon-nil, regardless ofinhibit-quit.
This variable determines whether Emacs should quit when
quit-flagis set to a value other thannil. Ifinhibit-quitis non-nil, thenquit-flaghas no special effect.
This function signals the
quitcondition with(signal 'quit nil). This is the same thing that quitting does. (Seesignalin Errors.)
You can specify a character other than C-g to use for quitting.
See the function set-input-mode in Terminal Input.
Most Emacs commands can use a prefix argument, a number
specified before the command itself. (Don't confuse prefix arguments
with prefix keys.) The prefix argument is at all times represented by a
value, which may be nil, meaning there is currently no prefix
argument. Each command may use the prefix argument or ignore it.
There are two representations of the prefix argument: raw and numeric. The editor command loop uses the raw representation internally, and so do the Lisp variables that store the information, but commands can request either representation.
Here are the possible values of a raw prefix argument:
nil, meaning there is no prefix argument. Its numeric value is
1, but numerous commands make a distinction between nil and the
integer 1.
-. This indicates that M-- or C-u - was
typed, without following digits. The equivalent numeric value is
−1, but some commands make a distinction between the integer
−1 and the symbol -.
We illustrate these possibilities by calling the following function with various prefixes:
(defun display-prefix (arg)
"Display the value of the raw prefix arg."
(interactive "P")
(message "%s" arg))
Here are the results of calling display-prefix with various
raw prefix arguments:
M-x display-prefix -| nil
C-u M-x display-prefix -| (4)
C-u C-u M-x display-prefix -| (16)
C-u 3 M-x display-prefix -| 3
M-3 M-x display-prefix -| 3 ; (Same as C-u 3.)
C-u - M-x display-prefix -| -
M-- M-x display-prefix -| - ; (Same as C-u -.)
C-u - 7 M-x display-prefix -| -7
M-- 7 M-x display-prefix -| -7 ; (Same as C-u -7.)
Emacs uses two variables to store the prefix argument:
prefix-arg and current-prefix-arg. Commands such as
universal-argument that set up prefix arguments for other
commands store them in prefix-arg. In contrast,
current-prefix-arg conveys the prefix argument to the current
command, so setting it has no effect on the prefix arguments for future
commands.
Normally, commands specify which representation to use for the prefix
argument, either numeric or raw, in the interactive declaration.
(See Using Interactive.) Alternatively, functions may look at the
value of the prefix argument directly in the variable
current-prefix-arg, but this is less clean.
This function returns the numeric meaning of a valid raw prefix argument value, arg. The argument may be a symbol, a number, or a list. If it is
nil, the value 1 is returned; if it is-, the value −1 is returned; if it is a number, that number is returned; if it is a list, the car of that list (which should be a number) is returned.
This variable holds the raw prefix argument for the current command. Commands may examine it directly, but the usual method for accessing it is with
(interactive "P").
The value of this variable is the raw prefix argument for the next editing command. Commands such as
universal-argumentthat specify prefix arguments for the following command work by setting this variable.
The following commands exist to set up prefix arguments for the following command. Do not call them for any other reason.
This command reads input and specifies a prefix argument for the following command. Don't call this command yourself unless you know what you are doing.
This command adds to the prefix argument for the following command. The argument arg is the raw prefix argument as it was before this command; it is used to compute the updated prefix argument. Don't call this command yourself unless you know what you are doing.
This command adds to the numeric argument for the next command. The argument arg is the raw prefix argument as it was before this command; its value is negated to form the new prefix argument. Don't call this command yourself unless you know what you are doing.
The Emacs command loop is entered automatically when Emacs starts up. This top-level invocation of the command loop never exits; it keeps running as long as Emacs does. Lisp programs can also invoke the command loop. Since this makes more than one activation of the command loop, we call it recursive editing. A recursive editing level has the effect of suspending whatever command invoked it and permitting the user to do arbitrary editing before resuming that command.
The commands available during recursive editing are the same ones available in the top-level editing loop and defined in the keymaps. Only a few special commands exit the recursive editing level; the others return to the recursive editing level when they finish. (The special commands for exiting are always available, but they do nothing when recursive editing is not in progress.)
All command loops, including recursive ones, set up all-purpose error handlers so that an error in a command run from the command loop will not exit the loop.
Minibuffer input is a special kind of recursive editing. It has a few special wrinkles, such as enabling display of the minibuffer and the minibuffer window, but fewer than you might suppose. Certain keys behave differently in the minibuffer, but that is only because of the minibuffer's local map; if you switch windows, you get the usual Emacs commands.
To invoke a recursive editing level, call the function
recursive-edit. This function contains the command loop; it also
contains a call to catch with tag exit, which makes it
possible to exit the recursive editing level by throwing to exit
(see Catch and Throw). If you throw a value other than t,
then recursive-edit returns normally to the function that called
it. The command C-M-c (exit-recursive-edit) does this.
Throwing a t value causes recursive-edit to quit, so that
control returns to the command loop one level up. This is called
aborting, and is done by C-] (abort-recursive-edit).
Most applications should not use recursive editing, except as part of using the minibuffer. Usually it is more convenient for the user if you change the major mode of the current buffer temporarily to a special major mode, which should have a command to go back to the previous mode. (The e command in Rmail uses this technique.) Or, if you wish to give the user different text to edit “recursively”, create and select a new buffer in a special mode. In this mode, define a command to complete the processing and go back to the previous buffer. (The m command in Rmail does this.)
Recursive edits are useful in debugging. You can insert a call to
debug into a function definition as a sort of breakpoint, so that
you can look around when the function gets there. debug invokes
a recursive edit but also provides the other features of the debugger.
Recursive editing levels are also used when you type C-r in
query-replace or use C-x q (kbd-macro-query).
This function invokes the editor command loop. It is called automatically by the initialization of Emacs, to let the user begin editing. When called from a Lisp program, it enters a recursive editing level.
In the following example, the function
simple-recfirst advances point one word, then enters a recursive edit, printing out a message in the echo area. The user can then do any editing desired, and then type C-M-c to exit and continue executingsimple-rec.(defun simple-rec () (forward-word 1) (message "Recursive edit in progress") (recursive-edit) (forward-word 1)) => simple-rec (simple-rec) => nil
This function exits from the innermost recursive edit (including minibuffer input). Its definition is effectively
(throw 'exit nil).
This function aborts the command that requested the innermost recursive edit (including minibuffer input), by signaling
quitafter exiting the recursive edit. Its definition is effectively(throw 'exit t). See Quitting.
This function exits all recursive editing levels; it does not return a value, as it jumps completely out of any computation directly back to the main command loop.
This function returns the current depth of recursive edits. When no recursive edit is active, it returns 0.
Disabling a command marks the command as requiring user confirmation before it can be executed. Disabling is used for commands which might be confusing to beginning users, to prevent them from using the commands by accident.
The low-level mechanism for disabling a command is to put a
non-nil disabled property on the Lisp symbol for the
command. These properties are normally set up by the user's
init file (see Init File) with Lisp expressions such as this:
(put 'upcase-region 'disabled t)
For a few commands, these properties are present by default (you can remove them in your init file if you wish).
If the value of the disabled property is a string, the message
saying the command is disabled includes that string. For example:
(put 'delete-region 'disabled
"Text deleted this way cannot be yanked back!\n")
See Disabling, for the details on what happens when a disabled command is invoked interactively. Disabling a command has no effect on calling it as a function from Lisp programs.
Allow command to be executed without special confirmation from now on, and (if the user confirms) alter the user's init file (see Init File) so that this will apply to future sessions.
Require special confirmation to execute command from now on, and (if the user confirms) alter the user's init file so that this will apply to future sessions.
When the user invokes a disabled command interactively, this normal hook is run instead of the disabled command. The hook functions can use
this-command-keysto determine what the user typed to run the command, and thus find the command itself. See Hooks.By default,
disabled-command-hookcontains a function that asks the user whether to proceed.
The command loop keeps a history of the complex commands that have
been executed, to make it convenient to repeat these commands. A
complex command is one for which the interactive argument reading
uses the minibuffer. This includes any M-x command, any
M-: command, and any command whose interactive
specification reads an argument from the minibuffer. Explicit use of
the minibuffer during the execution of the command itself does not cause
the command to be considered complex.
This variable's value is a list of recent complex commands, each represented as a form to evaluate. It continues to accumulate all complex commands for the duration of the editing session, but when it reaches the maximum size (specified by the variable
history-length), the oldest elements are deleted as new ones are added.command-history => ((switch-to-buffer "chistory.texi") (describe-key "^X^[") (visit-tags-table "~/emacs/src/") (find-tag "repeat-complex-command"))
This history list is actually a special case of minibuffer history (see Minibuffer History), with one special twist: the elements are expressions rather than strings.
There are a number of commands devoted to the editing and recall of
previous commands. The commands repeat-complex-command, and
list-command-history are described in the user manual
(see Repetition). Within the
minibuffer, the usual minibuffer history commands are available.
A keyboard macro is a canned sequence of input events that can be considered a command and made the definition of a key. The Lisp representation of a keyboard macro is a string or vector containing the events. Don't confuse keyboard macros with Lisp macros (see Macros).
This function executes kbdmacro as a sequence of events. If kbdmacro is a string or vector, then the events in it are executed exactly as if they had been input by the user. The sequence is not expected to be a single key sequence; normally a keyboard macro definition consists of several key sequences concatenated.
If kbdmacro is a symbol, then its function definition is used in place of kbdmacro. If that is another symbol, this process repeats. Eventually the result should be a string or vector. If the result is not a symbol, string, or vector, an error is signaled.
The argument count is a repeat count; kbdmacro is executed that many times. If count is omitted or
nil, kbdmacro is executed once. If it is 0, kbdmacro is executed over and over until it encounters an error or a failing search.See Reading One Event, for an example of using
execute-kbd-macro.
This variable contains the string or vector that defines the keyboard macro that is currently executing. It is
nilif no macro is currently executing. A command can test this variable so as to behave differently when run from an executing macro. Do not set this variable yourself.
This variable indicates whether a keyboard macro is being defined. A command can test this variable so as to behave differently while a macro is being defined. The commands
start-kbd-macroandend-kbd-macroset this variable—do not set it yourself.The variable is always local to the current terminal and cannot be buffer-local. See Multiple Displays.
This variable is the definition of the most recently defined keyboard macro. Its value is a string or vector, or
nil.The variable is always local to the current terminal and cannot be buffer-local. See Multiple Displays.
This normal hook (see Standard Hooks) is run when a keyboard macro terminates, regardless of what caused it to terminate (reaching the macro end or an error which ended the macro prematurely).
The bindings between input events and commands are recorded in data structures called keymaps. Each binding in a keymap associates (or binds) an individual event type either to another keymap or to a command. When an event type is bound to a keymap, that keymap is used to look up the next input event; this continues until a command is found. The whole process is called key lookup.
A keymap is a table mapping event types to definitions (which can be any Lisp objects, though only certain types are meaningful for execution by the command loop). Given an event (or an event type) and a keymap, Emacs can get the event's definition. Events include characters, function keys, and mouse actions (see Input Events).
A sequence of input events that form a unit is called a key sequence, or key for short. A sequence of one event is always a key sequence, and so are some multi-event sequences.
A keymap determines a binding or definition for any key sequence. If the key sequence is a single event, its binding is the definition of the event in the keymap. The binding of a key sequence of more than one event is found by an iterative process: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up.
If the binding of a key sequence is a keymap, we call the key sequence
a prefix key. Otherwise, we call it a complete key (because
no more events can be added to it). If the binding is nil,
we call the key undefined. Examples of prefix keys are C-c,
C-x, and C-x 4. Examples of defined complete keys are
X, <RET>, and C-x 4 C-f. Examples of undefined complete
keys are C-x C-g, and C-c 3. See Prefix Keys, for more
details.
The rule for finding the binding of a key sequence assumes that the intermediate bindings (found for the events before the last) are all keymaps; if this is not so, the sequence of events does not form a unit—it is not really one key sequence. In other words, removing one or more events from the end of any valid key sequence must always yield a prefix key. For example, C-f C-n is not a key sequence; C-f is not a prefix key, so a longer sequence starting with C-f cannot be a key sequence.
The set of possible multi-event key sequences depends on the bindings for prefix keys; therefore, it can be different for different keymaps, and can change when bindings are changed. However, a one-event sequence is always a key sequence, because it does not depend on any prefix keys for its well-formedness.
At any time, several primary keymaps are active—that is, in use for finding key bindings. These are the global map, which is shared by all buffers; the local keymap, which is usually associated with a specific major mode; and zero or more minor mode keymaps, which belong to currently enabled minor modes. (Not all minor modes have keymaps.) The local keymap bindings shadow (i.e., take precedence over) the corresponding global bindings. The minor mode keymaps shadow both local and global keymaps. See Active Keymaps, for details.
A keymap is a list whose car is the symbol keymap. The
remaining elements of the list define the key bindings of the keymap.
Use the function keymapp (see below) to test whether an object is
a keymap.
Several kinds of elements may appear in a keymap, after the symbol
keymap that begins it:
(type . binding)(t . binding)When a keymap contains a vector, it always defines a binding for each
ascii character, even if the vector contains nil for that
character. Such a binding of nil overrides any default key
binding in the keymap, for ascii characters. However, default
bindings are still meaningful for events other than ascii
characters. A binding of nil does not override
lower-precedence keymaps; thus, if the local map gives a binding of
nil, Emacs uses the binding from the global map.
Keymaps do not directly record bindings for the meta characters.
Instead, meta characters are regarded for purposes of key lookup as
sequences of two characters, the first of which is <ESC> (or
whatever is currently the value of meta-prefix-char). Thus, the
key M-a is internally represented as <ESC> a, and its
global binding is found at the slot for a in esc-map
(see Prefix Keys).
This conversion applies only to characters, not to function keys or other input events; thus, M-<end> has nothing to do with <ESC> <end>.
Here as an example is the local keymap for Lisp mode, a sparse keymap. It defines bindings for <DEL> and <TAB>, plus C-c C-l, M-C-q, and M-C-x.
lisp-mode-map
=>
(keymap
;; <TAB>
(9 . lisp-indent-line)
;; <DEL>
(127 . backward-delete-char-untabify)
(3 keymap
;; C-c C-l
(12 . run-lisp))
(27 keymap
;; M-C-q, treated as <ESC> C-q
(17 . indent-sexp)
;; M-C-x, treated as <ESC> C-x
(24 . lisp-send-defun)))
This function returns
tif object is a keymap,nilotherwise. More precisely, this function tests for a list whose car iskeymap.(keymapp '(keymap)) => t (keymapp (current-global-map)) => t
Here we describe the functions for creating keymaps.
This function creates and returns a new full keymap. That keymap contains a char-table (see Char-Tables) with 384 slots: the first 128 slots are for defining all the ascii characters, the next 128 slots are for 8-bit European characters, and each one of the final 128 slots is for one character set of non-ascii characters supported by Emacs. The new keymap initially binds all these characters to
nil, and does not bind any other kind of event.(make-keymap) => (keymap [nil nil nil ... nil nil])If you specify prompt, that becomes the overall prompt string for the keymap. The prompt string should be provided for menu keymaps (see Defining Menus).
This function creates and returns a new sparse keymap with no entries. The new keymap does not contain a char-table, unlike
make-keymap, and does not bind any events. The argument prompt specifies a prompt string, as inmake-keymap.(make-sparse-keymap) => (keymap)
This function returns a copy of keymap. Any keymaps that appear directly as bindings in keymap are also copied recursively, and so on to any number of levels. However, recursive copying does not take place when the definition of a character is a symbol whose function definition is a keymap; the same symbol appears in the new copy.
(setq map (copy-keymap (current-local-map))) => (keymap ;; (This implements meta characters.) (27 keymap (83 . center-paragraph) (115 . center-line)) (9 . tab-to-tab-stop)) (eq map (current-local-map)) => nil (equal map (current-local-map)) => t
A keymap can inherit the bindings of another keymap, which we call the parent keymap. Such a keymap looks like this:
(keymap bindings... . parent-keymap)
The effect is that this keymap inherits all the bindings of parent-keymap, whatever they may be at the time a key is looked up, but can add to them or override them with bindings.
If you change the bindings in parent-keymap using define-key
or other key-binding functions, these changes are visible in the
inheriting keymap unless shadowed by bindings. The converse is
not true: if you use define-key to change the inheriting keymap,
that affects bindings, but has no effect on parent-keymap.
The proper way to construct a keymap with a parent is to use
set-keymap-parent; if you have code that directly constructs a
keymap with a parent, please convert the program to use
set-keymap-parent instead.
This returns the parent keymap of keymap. If keymap has no parent,
keymap-parentreturnsnil.
This sets the parent keymap of keymap to parent, and returns parent. If parent is
nil, this function gives keymap no parent at all.If keymap has submaps (bindings for prefix keys), they too receive new parent keymaps that reflect what parent specifies for those prefix keys.
Here is an example showing how to make a keymap that inherits
from text-mode-map:
(let ((map (make-sparse-keymap)))
(set-keymap-parent map text-mode-map)
map)
A prefix key is a key sequence whose binding is a keymap. The
keymap defines what to do with key sequences that extend the prefix key.
For example, C-x is a prefix key, and it uses a keymap that is
also stored in the variable ctl-x-map. This keymap defines
bindings for key sequences starting with C-x.
Some of the standard Emacs prefix keys use keymaps that are also found in Lisp variables:
esc-map is the global keymap for the <ESC> prefix key. Thus,
the global definitions of all meta characters are actually found here.
This map is also the function definition of ESC-prefix.
help-map is the global keymap for the C-h prefix key.
mode-specific-map is the global keymap for the prefix key
C-c. This map is actually global, not mode-specific, but its name
provides useful information about C-c in the output of C-h b
(display-bindings), since the main use of this prefix key is for
mode-specific bindings.
ctl-x-map is the global keymap used for the C-x prefix key.
This map is found via the function cell of the symbol
Control-X-prefix.
mule-keymap is the global keymap used for the C-x <RET>
prefix key.
ctl-x-4-map is the global keymap used for the C-x 4 prefix
key.
ctl-x-5-map is the global keymap used for the C-x 5 prefix
key.
2C-mode-map is the global keymap used for the C-x 6 prefix
key.
vc-prefix-map is the global keymap used for the C-x v prefix
key.
facemenu-keymap is the global keymap used for the M-g
prefix key.
The keymap binding of a prefix key is used for looking up the event
that follows the prefix key. (It may instead be a symbol whose function
definition is a keymap. The effect is the same, but the symbol serves
as a name for the prefix key.) Thus, the binding of C-x is the
symbol Control-X-prefix, whose function cell holds the keymap
for C-x commands. (The same keymap is also the value of
ctl-x-map.)
Prefix key definitions can appear in any active keymap. The definitions of C-c, C-x, C-h and <ESC> as prefix keys appear in the global map, so these prefix keys are always available. Major and minor modes can redefine a key as a prefix by putting a prefix key definition for it in the local map or the minor mode's map. See Active Keymaps.
If a key is defined as a prefix in more than one active map, then its various definitions are in effect merged: the commands defined in the minor mode keymaps come first, followed by those in the local map's prefix definition, and then by those from the global map.
In the following example, we make C-p a prefix key in the local
keymap, in such a way that C-p is identical to C-x. Then
the binding for C-p C-f is the function find-file, just
like C-x C-f. The key sequence C-p 6 is not found in any
active keymap.
(use-local-map (make-sparse-keymap))
=> nil
(local-set-key "\C-p" ctl-x-map)
=> nil
(key-binding "\C-p\C-f")
=> find-file
(key-binding "\C-p6")
=> nil
This function prepares symbol for use as a prefix key's binding: it creates a sparse keymap and stores it as symbol's function definition. Subsequently binding a key sequence to symbol will make that key sequence into a prefix key. The return value is
symbol.This function also sets symbol as a variable, with the keymap as its value. But if mapvar is non-
nil, it sets mapvar as a variable instead.If prompt is non-
nil, that becomes the overall prompt string for the keymap. The prompt string should be given for menu keymaps (see Defining Menus).
Emacs normally contains many keymaps; at any given time, just a few of them are active in that they participate in the interpretation of user input. These are the global keymap, the current buffer's local keymap, and the keymaps of any enabled minor modes.
The global keymap holds the bindings of keys that are defined
regardless of the current buffer, such as C-f. The variable
global-map holds this keymap, which is always active.
Each buffer may have another keymap, its local keymap, which may
contain new or overriding definitions for keys. The current buffer's
local keymap is always active except when overriding-local-map
overrides it. Text properties can specify an alternative local map for
certain parts of the buffer; see Special Properties.
Each minor mode can have a keymap; if it does, the keymap is active when the minor mode is enabled.
The variable overriding-local-map, if non-nil, specifies
another local keymap that overrides the buffer's local map and all the
minor mode keymaps.
All the active keymaps are used together to determine what command to execute when a key is entered. Emacs searches these maps one by one, in order of decreasing precedence, until it finds a binding in one of the maps. The procedure for searching a single keymap is called key lookup; see Key Lookup.
Normally, Emacs first searches for the key in the minor mode maps, in
the order specified by minor-mode-map-alist; if they do not
supply a binding for the key, Emacs searches the local map; if that too
has no binding, Emacs then searches the global map. However, if
overriding-local-map is non-nil, Emacs searches that map
first, before the global map.
Since every buffer that uses the same major mode normally uses the
same local keymap, you can think of the keymap as local to the mode. A
change to the local keymap of a buffer (using local-set-key, for
example) is seen also in the other buffers that share that keymap.
The local keymaps that are used for Lisp mode and some other major
modes exist even if they have not yet been used. These local maps are
the values of variables such as lisp-mode-map. For most major
modes, which are less frequently used, the local keymap is constructed
only when the mode is used for the first time in a session.
The minibuffer has local keymaps, too; they contain various completion and exit commands. See Intro to Minibuffers.
Emacs has other keymaps that are used in a different way—translating
events within read-key-sequence. See Translating Input.
See Standard Keymaps, for a list of standard keymaps.
This variable contains the default global keymap that maps Emacs keyboard input to commands. The global keymap is normally this keymap. The default global keymap is a full keymap that binds
self-insert-commandto all of the printing characters.It is normal practice to change the bindings in the global map, but you should not assign this variable any value other than the keymap it starts out with.
This function returns the current global keymap. This is the same as the value of
global-mapunless you change one or the other.(current-global-map) => (keymap [set-mark-command beginning-of-line ... delete-backward-char])
This function returns the current buffer's local keymap, or
nilif it has none. In the following example, the keymap for the ‘*scratch*’ buffer (using Lisp Interaction mode) is a sparse keymap in which the entry for <ESC>, ascii code 27, is another sparse keymap.(current-local-map) => (keymap (10 . eval-print-last-sexp) (9 . lisp-indent-line) (127 . backward-delete-char-untabify) (27 keymap (24 . eval-defun) (17 . indent-sexp)))
This function returns a list of the keymaps of currently enabled minor modes.
This function makes keymap the new current global keymap. It returns
nil.It is very unusual to change the global keymap.
This function makes keymap the new local keymap of the current buffer. If keymap is
nil, then the buffer has no local keymap.use-local-mapreturnsnil. Most major mode commands use this function.
This variable is an alist describing keymaps that may or may not be active according to the values of certain variables. Its elements look like this:
(variable . keymap)The keymap keymap is active whenever variable has a non-
nilvalue. Typically variable is the variable that enables or disables a minor mode. See Keymaps and Minor Modes.Note that elements of
minor-mode-map-alistdo not have the same structure as elements ofminor-mode-alist. The map must be the cdr of the element; a list with the map as the second element will not do. The cdr can be either a keymap (a list) or a symbol whose function definition is a keymap.When more than one minor mode keymap is active, their order of priority is the order of
minor-mode-map-alist. But you should design minor modes so that they don't interfere with each other. If you do this properly, the order will not matter.See Keymaps and Minor Modes, for more information about minor modes. See also
minor-mode-key-binding(see Functions for Key Lookup).
This variable allows major modes to override the key bindings for particular minor modes. The elements of this alist look like the elements of
minor-mode-map-alist:(variable.keymap).If a variable appears as an element of
minor-mode-overriding-map-alist, the map specified by that element totally replaces any map specified for the same variable inminor-mode-map-alist.
minor-mode-overriding-map-alistis automatically buffer-local in all buffers.
If non-
nil, this variable holds a keymap to use instead of the buffer's local keymap and instead of all the minor mode keymaps. This keymap, if any, overrides all other maps that would have been active, except for the current global map.
If non-
nil, this variable holds a keymap to use instead ofoverriding-local-map, the buffer's local keymap and all the minor mode keymaps.This variable is always local to the current terminal and cannot be buffer-local. See Multiple Displays. It is used to implement incremental search mode.
If this variable is non-
nil, the value ofoverriding-local-maporoverriding-terminal-local-mapcan affect the display of the menu bar. The default value isnil, so those map variables have no effect on the menu bar.Note that these two map variables do affect the execution of key sequences entered using the menu bar, even if they do not affect the menu bar display. So if a menu bar key sequence comes in, you should clear the variables before looking up and executing that key sequence. Modes that use the variables would typically do this anyway; normally they respond to events that they do not handle by “unreading” them and exiting.
This variable holds a keymap for special events. If an event type has a binding in this keymap, then it is special, and the binding for the event is run directly by
read-event. See Special Events.
Key lookup is the process of finding the binding of a key sequence from a given keymap. Actual execution of the binding is not part of key lookup.
Key lookup uses just the event type of each event in the key sequence;
the rest of the event is ignored. In fact, a key sequence used for key
lookup may designate mouse events with just their types (symbols)
instead of with entire mouse events (lists). See Input Events. Such
a “key-sequence” is insufficient for command-execute to run,
but it is sufficient for looking up or rebinding a key.
When the key sequence consists of multiple events, key lookup processes the events sequentially: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up. (The binding thus found for the last event may or may not be a keymap.) Thus, the process of key lookup is defined in terms of a simpler process for looking up a single event in a keymap. How that is done depends on the type of object associated with the event in that keymap.
Let's use the term keymap entry to describe the value found by
looking up an event type in a keymap. (This doesn't include the item
string and other extra elements in menu key bindings, because
lookup-key and other key lookup functions don't include them in
the returned value.) While any Lisp object may be stored in a keymap as
a keymap entry, not all make sense for key lookup. Here is a table of
the meaningful kinds of keymap entries:
nilnil means that the events used so far in the lookup form an
undefined key. When a keymap fails to mention an event type at all, and
has no default binding, that is equivalent to a binding of nil
for that event type.
keymap, then the list
is a keymap, and is treated as a keymap (see above).
lambda, then the list is a
lambda expression. This is presumed to be a command, and is treated as
such (see above).
(othermap . othertype)
When key lookup encounters an indirect entry, it looks up instead the binding of othertype in othermap and uses that.
This feature permits you to define one key as an alias for another key.
For example, an entry whose car is the keymap called esc-map
and whose cdr is 32 (the code for <SPC>) means, “Use the global
binding of Meta-<SPC>, whatever that may be.”
Note that keymaps and keyboard macros (strings and vectors) are not
valid functions, so a symbol with a keymap, string, or vector as its
function definition is invalid as a function. It is, however, valid as
a key binding. If the definition is a keyboard macro, then the symbol
is also valid as an argument to command-execute
(see Interactive Call).
The symbol undefined is worth special mention: it means to treat
the key as undefined. Strictly speaking, the key is defined, and its
binding is the command undefined; but that command does the same
thing that is done automatically for an undefined key: it rings the bell
(by calling ding) but does not signal an error.
undefined is used in local keymaps to override a global key
binding and make the key “undefined” locally. A local binding of
nil would fail to do this because it would not override the
global binding.
In short, a keymap entry may be a keymap, a command, a keyboard macro,
a symbol that leads to one of them, or an indirection or nil.
Here is an example of a sparse keymap with two characters bound to
commands and one bound to another keymap. This map is the normal value
of emacs-lisp-mode-map. Note that 9 is the code for <TAB>,
127 for <DEL>, 27 for <ESC>, 17 for C-q and 24 for
C-x.
(keymap (9 . lisp-indent-line)
(127 . backward-delete-char-untabify)
(27 keymap (17 . indent-sexp) (24 . eval-defun)))
Here are the functions and variables pertaining to key lookup.
This function returns the definition of key in keymap. All the other functions described in this chapter that look up keys use
lookup-key. Here are examples:(lookup-key (current-global-map) "\C-x\C-f") => find-file (lookup-key (current-global-map) "\C-x\C-f12345") => 2If the string or vector key is not a valid key sequence according to the prefix keys specified in keymap, it must be “too long” and have extra events at the end that do not fit into a single key sequence. Then the value is a number, the number of events at the front of key that compose a complete key.
If accept-defaults is non-
nil, thenlookup-keyconsiders default bindings as well as bindings for the specific events in key. Otherwise,lookup-keyreports only bindings for the specific sequence key, ignoring default bindings except when you explicitly ask about them. (To do this, supplytas an element of key; see Format of Keymaps.)If key contains a meta character (not a function key), that character is implicitly replaced by a two-character sequence: the value of
meta-prefix-char, followed by the corresponding non-meta character. Thus, the first example below is handled by conversion into the second example.(lookup-key (current-global-map) "\M-f") => forward-word (lookup-key (current-global-map) "\ef") => forward-wordUnlike
read-key-sequence, this function does not modify the specified events in ways that discard information (see Key Sequence Input). In particular, it does not convert letters to lower case and it does not change drag events to clicks.
This function returns the binding for key in the current keymaps, trying all the active keymaps. The result is
nilif key is undefined in the keymaps.The argument accept-defaults controls checking for default bindings, as in
lookup-key(above).An error is signaled if key is not a string or a vector.
(key-binding "\C-x\C-f") => find-file
This function returns the binding for key in the current local keymap, or
nilif it is undefined there.The argument accept-defaults controls checking for default bindings, as in
lookup-key(above).
This function returns the binding for command key in the current global keymap, or
nilif it is undefined there.The argument accept-defaults controls checking for default bindings, as in
lookup-key(above).
This function returns a list of all the active minor mode bindings of key. More precisely, it returns an alist of pairs
(modename.binding), where modename is the variable that enables the minor mode, and binding is key's binding in that mode. If key has no minor-mode bindings, the value isnil.If the first binding found is not a prefix definition (a keymap or a symbol defined as a keymap), all subsequent bindings from other minor modes are omitted, since they would be completely shadowed. Similarly, the list omits non-prefix bindings that follow prefix bindings.
The argument accept-defaults controls checking for default bindings, as in
lookup-key(above).
This variable is the meta-prefix character code. It is used when translating a meta character to a two-character sequence so it can be looked up in a keymap. For useful results, the value should be a prefix event (see Prefix Keys). The default value is 27, which is the ascii code for <ESC>.
As long as the value of
meta-prefix-charremains 27, key lookup translates M-b into <ESC> b, which is normally defined as thebackward-wordcommand. However, if you were to setmeta-prefix-charto 24, the code for C-x, then Emacs will translate M-b into C-x b, whose standard binding is theswitch-to-buffercommand. (Don't actually do this!) Here is an illustration of what would happen:meta-prefix-char ; The default value. => 27 (key-binding "\M-b") => backward-word ?\C-x ; The print representation => 24 ; of a character. (setq meta-prefix-char 24) => 24 (key-binding "\M-b") => switch-to-buffer ; Now, typing M-b is ; like typing C-x b. (setq meta-prefix-char 27) ; Avoid confusion! => 27 ; Restore the default value!This translation of one event into two happens only for characters, not for other kinds of input events. Thus, M-<F1>, a function key, is not converted into <ESC> <F1>.
The way to rebind a key is to change its entry in a keymap. If you
change a binding in the global keymap, the change is effective in all
buffers (though it has no direct effect in buffers that shadow the
global binding with a local one). If you change the current buffer's
local map, that usually affects all buffers using the same major mode.
The global-set-key and local-set-key functions are
convenient interfaces for these operations (see Key Binding Commands). You can also use define-key, a more general
function; then you must specify explicitly the map to change.
In writing the key sequence to rebind, it is good to use the special
escape sequences for control and meta characters (see String Type).
The syntax ‘\C-’ means that the following character is a control
character and ‘\M-’ means that the following character is a meta
character. Thus, the string "\M-x" is read as containing a
single M-x, "\C-f" is read as containing a single
C-f, and "\M-\C-x" and "\C-\M-x" are both read as
containing a single C-M-x. You can also use this escape syntax in
vectors, as well as others that aren't allowed in strings; one example
is ‘[?\C-\H-x home]’. See Character Type.
The key definition and lookup functions accept an alternate syntax for
event types in a key sequence that is a vector: you can use a list
containing modifier names plus one base event (a character or function
key name). For example, (control ?a) is equivalent to
?\C-a and (hyper control left) is equivalent to
C-H-left. One advantage of such lists is that the precise
numeric codes for the modifier bits don't appear in compiled files.
For the functions below, an error is signaled if keymap is not a keymap or if key is not a string or vector representing a key sequence. You can use event types (symbols) as shorthand for events that are lists.
This function sets the binding for key in keymap. (If key is more than one event long, the change is actually made in another keymap reached from keymap.) The argument binding can be any Lisp object, but only certain types are meaningful. (For a list of meaningful types, see Key Lookup.) The value returned by
define-keyis binding.Every prefix of key must be a prefix key (i.e., bound to a keymap) or undefined; otherwise an error is signaled. If some prefix of key is undefined, then
define-keydefines it as a prefix key so that the rest of key can be defined as specified.If there was previously no binding for key in keymap, the new binding is added at the beginning of keymap. The order of bindings in a keymap makes no difference in most cases, but it does matter for menu keymaps (see Menu Keymaps).
Here is an example that creates a sparse keymap and makes a number of bindings in it:
(setq map (make-sparse-keymap))
=> (keymap)
(define-key map "\C-f" 'forward-char)
=> forward-char
map
=> (keymap (6 . forward-char))
;; Build sparse submap for C-x and bind f in that.
(define-key map "\C-xf" 'forward-word)
=> forward-word
map
=> (keymap
(24 keymap ; C-x
(102 . forward-word)) ; f
(6 . forward-char)) ; C-f
;; Bind C-p to the ctl-x-map.
(define-key map "\C-p" ctl-x-map)
;; ctl-x-map
=> [nil ... find-file ... backward-kill-sentence]
;; Bind C-f to foo in the ctl-x-map.
(define-key map "\C-p\C-f" 'foo)
=> 'foo
map
=> (keymap ; Note foo in ctl-x-map.
(16 keymap [nil ... foo ... backward-kill-sentence])
(24 keymap
(102 . forward-word))
(6 . forward-char))
Note that storing a new binding for C-p C-f actually works by
changing an entry in ctl-x-map, and this has the effect of
changing the bindings of both C-p C-f and C-x C-f in the
default global map.
This function replaces olddef with newdef for any keys in keymap that were bound to olddef. In other words, olddef is replaced with newdef wherever it appears. The function returns
nil.For example, this redefines C-x C-f, if you do it in an Emacs with standard bindings:
(substitute-key-definition 'find-file 'find-file-read-only (current-global-map))If oldmap is non-
nil, that changes the behavior ofsubstitute-key-definition: the bindings in oldmap determine which keys to rebind. The rebindings still happen in keymap, not in oldmap. Thus, you can change one map under the control of the bindings in another. For example,(substitute-key-definition 'delete-backward-char 'my-funny-delete my-map global-map)puts the special deletion command in
my-mapfor whichever keys are globally bound to the standard deletion command.Here is an example showing a keymap before and after substitution:
(setq map '(keymap (?1 . olddef-1) (?2 . olddef-2) (?3 . olddef-1))) => (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1)) (substitute-key-definition 'olddef-1 'newdef map) => nil map => (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))
This function changes the contents of the full keymap keymap by making all the printing characters undefined. More precisely, it binds them to the command
undefined. This makes ordinary insertion of text impossible.suppress-keymapreturnsnil.If nodigits is
nil, thensuppress-keymapdefines digits to rundigit-argument, and - to runnegative-argument. Otherwise it makes them undefined like the rest of the printing characters.The
suppress-keymapfunction does not make it impossible to modify a buffer, as it does not suppress commands such asyankandquoted-insert. To prevent any modification of a buffer, make it read-only (see Read Only Buffers).Since this function modifies keymap, you would normally use it on a newly created keymap. Operating on an existing keymap that is used for some other purpose is likely to cause trouble; for example, suppressing
global-mapwould make it impossible to use most of Emacs.Most often,
suppress-keymapis used to initialize local keymaps of modes such as Rmail and Dired where insertion of text is not desirable and the buffer is read-only. Here is an example taken from the file emacs/lisp/dired.el, showing how the local keymap for Dired mode is set up:(setq dired-mode-map (make-keymap)) (suppress-keymap dired-mode-map) (define-key dired-mode-map "r" 'dired-rename-file) (define-key dired-mode-map "\C-d" 'dired-flag-file-deleted) (define-key dired-mode-map "d" 'dired-flag-file-deleted) (define-key dired-mode-map "v" 'dired-view-file) (define-key dired-mode-map "e" 'dired-find-file) (define-key dired-mode-map "f" 'dired-find-file) ...
This section describes some convenient interactive interfaces for
changing key bindings. They work by calling define-key.
People often use global-set-key in their init files
(see Init File) for simple customization. For example,
(global-set-key "\C-x\C-\\" 'next-line)
or
(global-set-key [?\C-x ?\C-\\] 'next-line)
or
(global-set-key [(control ?x) (control ?\\)] 'next-line)
redefines C-x C-\ to move down a line.
(global-set-key [M-mouse-1] 'mouse-set-point)
redefines the first (leftmost) mouse button, typed with the Meta key, to set point where you click.
Be careful when using non-ascii text characters in Lisp specifications of keys to bind. If these are read as multibyte text, as they usually will be in a Lisp file (see Loading Non-ASCII), you must type the keys as multibyte too. For instance, if you use this:
(global-set-key "ö" 'my-function) ; bind o-umlaut
or
(global-set-key ?ö 'my-function) ; bind o-umlaut
and your language environment is multibyte Latin-1, these commands actually bind the multibyte character with code 2294, not the unibyte Latin-1 character with code 246 (M-v). In order to use this binding, you need to enter the multibyte Latin-1 character as keyboard input. One way to do this is by using an appropriate input method (see Input Methods).
If you want to use a unibyte character in the key binding, you can
construct the key sequence string using multibyte-char-to-unibyte
or string-make-unibyte (see Converting Representations).
This function sets the binding of key in the current global map to definition.
(global-set-key key definition) == (define-key (current-global-map) key definition)
This function removes the binding of key from the current global map.
One use of this function is in preparation for defining a longer key that uses key as a prefix—which would not be allowed if key has a non-prefix binding. For example:
(global-unset-key "\C-l") => nil (global-set-key "\C-l\C-l" 'redraw-display) => nilThis function is implemented simply using
define-key:(global-unset-key key) == (define-key (current-global-map) key nil)
This function sets the binding of key in the current local keymap to definition.
(local-set-key key definition) == (define-key (current-local-map) key definition)
This function removes the binding of key from the current local map.
(local-unset-key key) == (define-key (current-local-map) key nil)
This section describes functions used to scan all the current keymaps for the sake of printing help information.
This function returns a list of all the keymaps that can be reached (via zero or more prefix keys) from keymap. The value is an association list with elements of the form
(key.map), where key is a prefix key whose definition in keymap is map.The elements of the alist are ordered so that the key increases in length. The first element is always
("" .keymap), because the specified keymap is accessible from itself with a prefix of no events.If prefix is given, it should be a prefix key sequence; then
accessible-keymapsincludes only the submaps whose prefixes start with prefix. These elements look just as they do in the value of(accessible-keymaps); the only difference is that some elements are omitted.In the example below, the returned alist indicates that the key <ESC>, which is displayed as ‘^[’, is a prefix key whose definition is the sparse keymap
(keymap (83 . center-paragraph) (115 . foo)).(accessible-keymaps (current-local-map)) =>(("" keymap (27 keymap ; Note this keymap for <ESC> is repeated below. (83 . center-paragraph) (115 . center-line)) (9 . tab-to-tab-stop)) ("^[" keymap (83 . center-paragraph) (115 . foo)))In the following example, C-h is a prefix key that uses a sparse keymap starting with
(keymap (118 . describe-variable)...). Another prefix, C-x 4, uses a keymap which is also the value of the variablectl-x-4-map. The eventmode-lineis one of several dummy events used as prefixes for mouse actions in special parts of a window.(accessible-keymaps (current-global-map)) => (("" keymap [set-mark-command beginning-of-line ... delete-backward-char]) ("^H" keymap (118 . describe-variable) ... (8 . help-for-help)) ("^X" keymap [x-flush-mouse-queue ... backward-kill-sentence]) ("^[" keymap [mark-sexp backward-sexp ... backward-kill-word]) ("^X4" keymap (15 . display-buffer) ...) ([mode-line] keymap (S-mouse-2 . mouse-split-window-horizontally) ...))These are not all the keymaps you would see in actuality.
This function is a subroutine used by the
where-iscommand (see Help). It returns a list of key sequences (of any length) that are bound to command in a set of keymaps.The argument command can be any object; it is compared with all keymap entries using
eq.If keymap is
nil, then the maps used are the current active keymaps, disregardingoverriding-local-map(that is, pretending its value isnil). If keymap is non-nil, then the maps searched are keymap and the global keymap. If keymap is a list of keymaps, only those keymaps are searched.Usually it's best to use
overriding-local-mapas the expression for keymap. Thenwhere-is-internalsearches precisely the keymaps that are active. To search only the global map, pass(keymap)(an empty keymap) as keymap.If firstonly is
non-ascii, then the value is a single string representing the first key sequence found, rather than a list of all possible key sequences. If firstonly ist, then the value is the first key sequence, except that key sequences consisting entirely of ascii characters (or meta variants of ascii characters) are preferred to all other key sequences.If noindirect is non-
nil,where-is-internaldoesn't follow indirect keymap bindings. This makes it possible to search for an indirect definition itself.(where-is-internal 'describe-function) => ("\^hf" "\^hd")
This function creates a listing of all current key bindings, and displays it in a buffer named ‘*Help*’. The text is grouped by modes—minor modes first, then the major mode, then global bindings.
If prefix is non-
nil, it should be a prefix key; then the listing includes only keys that start with prefix.The listing describes meta characters as <ESC> followed by the corresponding non-meta character.
When several characters with consecutive ascii codes have the same definition, they are shown together, as ‘firstchar..lastchar’. In this instance, you need to know the ascii codes to understand which characters this means. For example, in the default global map, the characters ‘<SPC> .. ~’ are described by a single line. <SPC> is ascii 32, ~ is ascii 126, and the characters between them include all the normal printing characters, (e.g., letters, digits, punctuation, etc.); all these characters are bound to
self-insert-command.
A keymap can define a menu as well as bindings for keyboard keys and mouse button. Menus are usually actuated with the mouse, but they can work with the keyboard also.
A keymap is suitable for menu use if it has an overall prompt string, which is a string that appears as an element of the keymap. (See Format of Keymaps.) The string should describe the purpose of the menu's commands. Emacs displays the overall prompt string as the menu title in some cases, depending on the toolkit (if any) used for displaying menus.6 Keyboard menus also display the overall prompt string.
The easiest way to construct a keymap with a prompt string is to specify
the string as an argument when you call make-keymap,
make-sparse-keymap or define-prefix-command
(see Creating Keymaps).
The order of items in the menu is the same as the order of bindings in
the keymap. Since define-key puts new bindings at the front, you
should define the menu items starting at the bottom of the menu and
moving to the top, if you care about the order. When you add an item to
an existing menu, you can specify its position in the menu using
define-key-after (see Modifying Menus).
The simpler and older way to define a menu keymap binding looks like this:
(item-string . real-binding)
The car, item-string, is the string to be displayed in the menu. It should be short—preferably one to three words. It should describe the action of the command it corresponds to.
You can also supply a second string, called the help string, as follows:
(item-string help . real-binding)
help specifies a “help-echo” string to display while the mouse
is on that item in the same way as help-echo text properties
(see Help display).
As far as define-key is concerned, item-string and
help-string are part of the event's binding. However,
lookup-key returns just real-binding, and only
real-binding is used for executing the key.
If real-binding is nil, then item-string appears in
the menu but cannot be selected.
If real-binding is a symbol and has a non-nil
menu-enable property, that property is an expression that
controls whether the menu item is enabled. Every time the keymap is
used to display a menu, Emacs evaluates the expression, and it enables
the menu item only if the expression's value is non-nil. When a
menu item is disabled, it is displayed in a “fuzzy” fashion, and
cannot be selected.
The menu bar does not recalculate which items are enabled every time you
look at a menu. This is because the X toolkit requires the whole tree
of menus in advance. To force recalculation of the menu bar, call
force-mode-line-update (see Mode Line Format).
You've probably noticed that menu items show the equivalent keyboard key sequence (if any) to invoke the same command. To save time on recalculation, menu display caches this information in a sublist in the binding, like this:
(item-string [help-string] (key-binding-data) . real-binding)
Don't put these sublists in the menu item yourself; menu display calculates them automatically. Don't mention keyboard equivalents in the item strings themselves, since that is redundant.
An extended-format menu item is a more flexible and also cleaner
alternative to the simple format. It consists of a list that starts
with the symbol menu-item. To define a non-selectable string,
the item looks like this:
(menu-item item-name)
A string starting with two or more dashes specifies a separator line; see Menu Separators.
To define a real menu item which can be selected, the extended format item looks like this:
(menu-item item-name real-binding
. item-property-list)
Here, item-name is an expression which evaluates to the menu item string. Thus, the string need not be a constant. The third element, real-binding, is the command to execute. The tail of the list, item-property-list, has the form of a property list which contains other information. Here is a table of the properties that are supported:
:enable formnil means yes). If the item is not enabled,
you can't really click on it.
:visible formnil means yes). If the item
does not appear, then the menu is displayed as if this item were
not defined at all.
:help helphelp-echo text properties (see Help display).
Note that this must be a constant string, unlike the help-echo
property for text and overlays.
:button (type . selected):toggle or
:radio. The cdr, selected, should be a form; the
result of evaluating it says whether this button is currently selected.
A toggle is a menu item which is labeled as either “on” or “off”
according to the value of selected. The command itself should
toggle selected, setting it to t if it is nil,
and to nil if it is t. Here is how the menu item
to toggle the debug-on-error flag is defined:
(menu-item "Debug on Error" toggle-debug-on-error
:button (:toggle
. (and (boundp 'debug-on-error)
debug-on-error)))
This works because toggle-debug-on-error is defined as a command
which toggles the variable debug-on-error.
Radio buttons are a group of menu items, in which at any time one
and only one is “selected.” There should be a variable whose value
says which one is selected at any time. The selected form for
each radio button in the group should check whether the variable has the
right value for selecting that button. Clicking on the button should
set the variable so that the button you clicked on becomes selected.
:key-sequence key-sequenceIf you specify the wrong key sequence, it has no effect; before Emacs
displays key-sequence in the menu, it verifies that
key-sequence is really equivalent to this menu item.
:key-sequence nilHowever, if the user has rebound this item's definition to a key
sequence, Emacs ignores the :keys property and finds the keyboard
equivalent anyway.
:keys string:filter filter-fnA menu separator is a kind of menu item that doesn't display any text–instead, it divides the menu into subparts with a horizontal line. A separator looks like this in the menu keymap:
(menu-item separator-type)
where separator-type is a string starting with two or more dashes.
In the simplest case, separator-type consists of only dashes.
That specifies the default kind of separator. (For compatibility,
"" and - also count as separators.)
Starting in Emacs 21, certain other values of separator-type specify a different style of separator. Here is a table of them:
"--no-line""--space""--single-line""--double-line""--single-dashed-line""--double-dashed-line""--shadow-etched-in""--shadow-etched-out""--shadow-etched-in-dash""--shadow-etched-out-dash""--shadow-double-etched-in""--shadow-double-etched-out""--shadow-double-etched-in-dash""--shadow-double-etched-out-dash"You can also give these names in another style, adding a colon after
the double-dash and replacing each single dash with capitalization of
the following word. Thus, "--:singleLine", is equivalent to
"--single-line".
Some systems and display toolkits don't really handle all of these separator types. If you use a type that isn't supported, the menu displays a similar kind of separator that is supported.
Sometimes it is useful to make menu items that use the “same”
command but with different enable conditions. The best way to do this
in Emacs now is with extended menu items; before that feature existed,
it could be done by defining alias commands and using them in menu
items. Here's an example that makes two aliases for
toggle-read-only and gives them different enable conditions:
(defalias 'make-read-only 'toggle-read-only)
(put 'make-read-only 'menu-enable '(not buffer-read-only))
(defalias 'make-writable 'toggle-read-only)
(put 'make-writable 'menu-enable 'buffer-read-only)
When using aliases in menus, often it is useful to display the
equivalent key bindings for the “real” command name, not the aliases
(which typically don't have any key bindings except for the menu
itself). To request this, give the alias symbol a non-nil
menu-alias property. Thus,
(put 'make-read-only 'menu-alias t)
(put 'make-writable 'menu-alias t)
causes menu items for make-read-only and make-writable to
show the keyboard bindings for toggle-read-only.
The usual way to make a menu keymap produce a menu is to make it the definition of a prefix key. (A Lisp program can explicitly pop up a menu and receive the user's choice—see Pop-Up Menus.)
If the prefix key ends with a mouse event, Emacs handles the menu keymap by popping up a visible menu, so that the user can select a choice with the mouse. When the user clicks on a menu item, the event generated is whatever character or symbol has the binding that brought about that menu item. (A menu item may generate a series of events if the menu has multiple levels or comes from the menu bar.)
It's often best to use a button-down event to trigger the menu. Then the user can select a menu item by releasing the button.
A single keymap can appear as multiple menu panes, if you explicitly arrange for this. The way to do this is to make a keymap for each pane, then create a binding for each of those maps in the main keymap of the menu. Give each of these bindings an item string that starts with ‘@’. The rest of the item string becomes the name of the pane. See the file lisp/mouse.el for an example of this. Any ordinary bindings with ‘@’-less item strings are grouped into one pane, which appears along with the other panes explicitly created for the submaps.
X toolkit menus don't have panes; instead, they can have submenus. Every nested keymap becomes a submenu, whether the item string starts with ‘@’ or not. In a toolkit version of Emacs, the only thing special about ‘@’ at the beginning of an item string is that the ‘@’ doesn't appear in the menu item.
You can also produce multiple panes or submenus from separate keymaps. The full definition of a prefix key always comes from merging the definitions supplied by the various active keymaps (minor mode, local, and global). When more than one of these keymaps is a menu, each of them makes a separate pane or panes (when Emacs does not use an X-toolkit) or a separate submenu (when using an X-toolkit). See Active Keymaps.
When a prefix key ending with a keyboard event (a character or function key) has a definition that is a menu keymap, the user can use the keyboard to choose a menu item.
Emacs displays the menu's overall prompt string followed by the
alternatives (the item strings of the bindings) in the echo area. If
the bindings don't all fit at once, the user can type <SPC> to see
the next line of alternatives. Successive uses of <SPC> eventually
get to the end of the menu and then cycle around to the beginning. (The
variable menu-prompt-more-char specifies which character is used
for this; <SPC> is the default.)
When the user has found the desired alternative from the menu, he or she should type the corresponding character—the one whose binding is that alternative.
This way of using menus in an Emacs-like editor was inspired by the Hierarkey system.
This variable specifies the character to use to ask to see the next line of a menu. Its initial value is 32, the code for <SPC>.
Here is a complete example of defining a menu keymap. It is the definition of the ‘Print’ submenu in the ‘Tools’ menu in the menu bar, and it uses the simple menu item format (see Simple Menu Items). First we create the keymap, and give it a name:
(defvar menu-bar-print-menu (make-sparse-keymap "Print"))
Next we define the menu items:
(define-key menu-bar-print-menu [ps-print-region]
'("Postscript Print Region" . ps-print-region-with-faces))
(define-key menu-bar-print-menu [ps-print-buffer]
'("Postscript Print Buffer" . ps-print-buffer-with-faces))
(define-key menu-bar-print-menu [separator-ps-print]
'("--"))
(define-key menu-bar-print-menu [print-region]
'("Print Region" . print-region))
(define-key menu-bar-print-menu [print-buffer]
'("Print Buffer" . print-buffer))
Note the symbols which the bindings are “made for”; these appear
inside square brackets, in the key sequence being defined. In some
cases, this symbol is the same as the command name; sometimes it is
different. These symbols are treated as “function keys”, but they are
not real function keys on the keyboard. They do not affect the
functioning of the menu itself, but they are “echoed” in the echo area
when the user selects from the menu, and they appear in the output of
where-is and apropos.
The binding whose definition is ("--") is a separator line.
Like a real menu item, the separator has a key symbol, in this case
separator-ps-print. If one menu has two separators, they must
have two different key symbols.
Here is code to define enable conditions for two of the commands in the menu:
(put 'print-region 'menu-enable 'mark-active)
(put 'ps-print-region-with-faces 'menu-enable 'mark-active)
Here is how we make this menu appear as an item in the parent menu:
(define-key menu-bar-tools-menu [print]
(cons "Print" menu-bar-print-menu))
Note that this incorporates the submenu keymap, which is the value of
the variable menu-bar-print-menu, rather than the symbol
menu-bar-print-menu itself. Using that symbol in the parent menu
item would be meaningless because menu-bar-print-menu is not a
command.
If you wanted to attach the same print menu to a mouse click, you can do it this way:
(define-key global-map [C-S-down-mouse-1]
menu-bar-print-menu)
We could equally well use an extended menu item (see Extended Menu Items) for print-region, like this:
(define-key menu-bar-print-menu [print-region]
'(menu-item "Print Region" print-region
:enable mark-active))
With the extended menu item, the enable condition is specified inside the menu item itself. If we wanted to make this item disappear from the menu entirely when the mark is inactive, we could do it this way:
(define-key menu-bar-print-menu [print-region]
'(menu-item "Print Region" print-region
:visible mark-active))
Most window systems allow each frame to have a menu bar—a
permanently displayed menu stretching horizontally across the top of the
frame. The items of the menu bar are the subcommands of the fake
“function key” menu-bar, as defined by all the active keymaps.
To add an item to the menu bar, invent a fake “function key” of your
own (let's call it key), and make a binding for the key sequence
[menu-bar key]. Most often, the binding is a menu keymap,
so that pressing a button on the menu bar item leads to another menu.
When more than one active keymap defines the same fake function key for the menu bar, the item appears just once. If the user clicks on that menu bar item, it brings up a single, combined menu containing all the subcommands of that item—the global subcommands, the local subcommands, and the minor mode subcommands.
The variable overriding-local-map is normally ignored when
determining the menu bar contents. That is, the menu bar is computed
from the keymaps that would be active if overriding-local-map
were nil. See Active Keymaps.
In order for a frame to display a menu bar, its menu-bar-lines
parameter must be greater than zero. Emacs uses just one line for the
menu bar itself; if you specify more than one line, the other lines
serve to separate the menu bar from the windows in the frame. We
recommend 1 or 2 as the value of menu-bar-lines. See Window Frame Parameters.
Here's an example of setting up a menu bar item:
(modify-frame-parameters (selected-frame)
'((menu-bar-lines . 2)))
;; Make a menu keymap (with a prompt string)
;; and make it the menu bar item's definition.
(define-key global-map [menu-bar words]
(cons "Words" (make-sparse-keymap "Words")))
;; Define specific subcommands in this menu.
(define-key global-map
[menu-bar words forward]
'("Forward word" . forward-word))
(define-key global-map
[menu-bar words backward]
'("Backward word" . backward-word))
A local keymap can cancel a menu bar item made by the global keymap by
rebinding the same fake function key with undefined as the
binding. For example, this is how Dired suppresses the ‘Edit’ menu
bar item:
(define-key dired-mode-map [menu-bar edit] 'undefined)
edit is the fake function key used by the global map for the
‘Edit’ menu bar item. The main reason to suppress a global
menu bar item is to regain space for mode-specific items.
Normally the menu bar shows global items followed by items defined by the local maps.
This variable holds a list of fake function keys for items to display at the end of the menu bar rather than in normal sequence. The default value is
(help-menu); thus, the ‘Help’ menu item normally appears at the end of the menu bar, following local menu items.
This normal hook is run whenever the user clicks on the menu bar, before displaying a submenu. You can use it to update submenus whose contents should vary.
A tool bar is a row of icons at the top of a frame, that execute commands when you click on them—in effect, a kind of graphical menu bar. Emacs supports tool bars starting with version 21.
The frame parameter tool-bar-lines (X resource ‘toolBar’)
controls how many lines' worth of height to reserve for the tool bar. A
zero value suppresses the tool bar. If the value is nonzero, and
auto-resize-tool-bars is non-nil, the tool bar expands and
contracts automatically as needed to hold the specified contents.
The tool bar contents are controlled by a menu keymap attached to a
fake “function key” called tool-bar (much like the way the menu
bar is controlled). So you define a tool bar item using
define-key, like this:
(define-key global-map [tool-bar key] item)
where key is a fake “function key” to distinguish this item from other items, and item is a menu item key binding (see Extended Menu Items), which says how to display this item and how it behaves.
The usual menu keymap item properties, :visible,
:enable, :button, and :filter, are useful in
tool bar bindings and have their normal meanings. The real-binding
in the item must be a command, not a keymap; in other words, it does not
work to define a tool bar icon as a prefix key.
The :help property specifies a “help-echo” string to display
while the mouse is on that item. This is displayed in the same way as
help-echo text properties (see Help display).
In addition, you should use the :image property;
this is how you specify the image to display in the tool bar:
:image imageIf image is a single image specification, Emacs draws the tool bar button in disabled state by applying an edge-detection algorithm to the image.
The default tool bar is defined so that items specific to editing do not
appear for major modes whose command symbol has a mode-class
property of special (see Major Mode Conventions). Major
modes may add items to the global bar by binding [tool-bar
foo] in their local map. It makes sense for some major modes to
replace the default tool bar items completely, since not many can be
accommodated conveniently, and the default bindings make this easy by
using an indirection through tool-bar-map.
By default, the global map binds
[tool-bar]as follows:(global-set-key [tool-bar] '(menu-item "tool bar" ignore :filter (lambda (ignore) tool-bar-map)))Thus the tool bar map is derived dynamically from the value of variable
tool-bar-mapand you should normally adjust the default (global) tool bar by changing that map. Major modes may replace the global bar completely by makingtool-bar-mapbuffer-local and set to a keymap containing only the desired items. Info mode provides an example.
There are two convenience functions for defining tool bar items, as follows.
This function adds an item to the tool bar by modifying
tool-bar-map. The image to use is defined by icon, which is the base name of an XPM, XBM or PBM image file to located byfind-image. Given a value ‘"exit"’, say, exit.xpm, exit.pbm and exit.xbm would be searched for in that order on a color display. On a monochrome display, the search order is ‘.pbm’, ‘.xbm’ and ‘.xpm’. The binding to use is the command def, and key is the fake function key symbol in the prefix keymap. The remaining arguments props are additional property list elements to add to the menu item specification.To define items in some local map, bind
`tool-bar-mapwithletaround calls of this function:(defvar foo-tool-bar-map (let ((tool-bar-map (make-sparse-keymap))) (tool-bar-add-item ...) ... tool-bar-map))
This command is a convenience for defining tool bar items which are consistent with existing menu bar bindings. The binding of command is looked up in the menu bar in map (default
global-map) and modified to add an image specification for icon, which is looked for in the same way as bytool-bar-add-item. The resulting binding is then placed intool-bar-map. map must contain an appropriate keymap bound to[menu-bar]. The remaining arguments props are additional property list elements to add to the menu item specification.
If this variable is non-
nil, the tool bar automatically resizes to show all defined tool bar items—but not larger than a quarter of the frame's height.
If this variable is non-
nil, tool bar items display in raised form when the mouse moves over them.
This variable specifies an extra margin to add around tool bar items. The value is an integer, a number of pixels. The default is 1.
This variable specifies the shadow width for tool bar items. The value is an integer, a number of pixels. The default is 3.
You can define a special meaning for clicking on a tool bar item with the shift, control, meta, etc., modifiers. You do this by setting up additional items that relate to the original item through the fake function keys. Specifically, the additional items should use the modified versions of the same fake function key used to name the original item.
Thus, if the original item was defined this way,
(define-key global-map [tool-bar shell]
'(menu-item "Shell" shell
:image (image :type xpm :file "shell.xpm")))
then here is how you can define clicking on the same tool bar image with the shift modifier:
(define-key global-map [tool-bar S-shell] 'some-command)
See Function Keys, for more information about how to add modifiers to function keys.
When you insert a new item in an existing menu, you probably want to
put it in a particular place among the menu's existing items. If you
use define-key to add the item, it normally goes at the front of
the menu. To put it elsewhere in the menu, use define-key-after:
Define a binding in map for key, with value binding, just like
define-key, but position the binding in map after the binding for the event after. The argument key should be of length one—a vector or string with just one element. But after should be a single event type—a symbol or a character, not a sequence. The new binding goes after the binding for after. If after istor is omitted, then the new binding goes last, at the end of the keymap. However, new bindings are added before any inherited keymap.Here is an example:
(define-key-after my-menu [drink] '("Drink" . drink-command) 'eat)makes a binding for the fake function key <DRINK> and puts it right after the binding for <EAT>.
Here is how to insert an item called ‘Work’ in the ‘Signals’ menu of Shell mode, after the item
break:(define-key-after (lookup-key shell-mode-map [menu-bar signals]) [work] '("Work" . work-command) 'break)
A mode is a set of definitions that customize Emacs and can be turned on and off while you edit. There are two varieties of modes: major modes, which are mutually exclusive and used for editing particular kinds of text, and minor modes, which provide features that users can enable individually.
This chapter describes how to write both major and minor modes, how to indicate them in the mode line, and how they run hooks supplied by the user. For related topics such as keymaps and syntax tables, see Keymaps, and Syntax Tables.
Major modes specialize Emacs for editing particular kinds of text. Each buffer has only one major mode at a time.
The least specialized major mode is called Fundamental mode.
This mode has no mode-specific definitions or variable settings, so each
Emacs command behaves in its default manner, and each option is in its
default state. All other major modes redefine various keys and options.
For example, Lisp Interaction mode provides special key bindings for
C-j (eval-print-last-sexp), <TAB>
(lisp-indent-line), and other keys.
When you need to write several editing commands to help you perform a specialized editing task, creating a new major mode is usually a good idea. In practice, writing a major mode is easy (in contrast to writing a minor mode, which is often difficult).
If the new mode is similar to an old one, it is often unwise to modify the old one to serve two purposes, since it may become harder to use and maintain. Instead, copy and rename an existing major mode definition and alter the copy—or define a derived mode (see Derived Modes). For example, Rmail Edit mode, which is in emacs/lisp/mail/rmailedit.el, is a major mode that is very similar to Text mode except that it provides two additional commands. Its definition is distinct from that of Text mode, but uses that of Text mode.
Even if the new mode is not an obvious derivative of any other mode,
it can be convenient to define it as a derivative of
fundamental-mode, so that define-derived-mode can
automatically enforce the most important coding conventions for you.
Rmail Edit mode offers an example of changing the major mode temporarily for a buffer, so it can be edited in a different way (with ordinary Emacs commands rather than Rmail commands). In such cases, the temporary major mode usually provides a command to switch back to the buffer's usual mode (Rmail mode, in this case). You might be tempted to present the temporary redefinitions inside a recursive edit and restore the usual ones when the user exits; but this is a bad idea because it constrains the user's options when it is done in more than one buffer: recursive edits must be exited most-recently-entered first. Using an alternative major mode avoids this limitation. See Recursive Editing.
The standard GNU Emacs Lisp library directory tree contains the code for several major modes, in files such as text-mode.el, texinfo.el, lisp-mode.el, c-mode.el, and rmail.el. They are found in various subdirectories of the lisp directory. You can study these libraries to see how modes are written. Text mode is perhaps the simplest major mode aside from Fundamental mode. Rmail mode is a complicated and specialized mode.
The code for existing major modes follows various coding conventions, including conventions for local keymap and syntax table initialization, global names, and hooks. Please follow these conventions when you define a new major mode.
This list of conventions is only partial, because each major mode should aim for consistency in general with other Emacs major modes. This makes Emacs as a whole more coherent. It is impossible to list here all the possible points where this issue might come up; if the Emacs developers point out an area where your major mode deviates from the usual conventions, please make it compatible.
describe-mode) in your mode will display this string.
The documentation string may include the special documentation substrings, ‘\[command]’, ‘\{keymap}’, and ‘\<keymap>’, which enable the documentation to adapt automatically to the user's own key bindings. See Keys in Documentation.
kill-all-local-variables. This is what gets rid of the
buffer-local variables of the major mode previously in effect.
major-mode to the
major mode command symbol. This is how describe-mode discovers
which documentation to print.
mode-name to the
“pretty” name of the mode, as a string. This string appears in the
mode line.
indent-line-function
to a suitable function, and probably customize other variables
for indentation.
use-local-map to install this local map. See Active Keymaps, for more information.
This keymap should be stored permanently in a global variable named
modename-mode-map. Normally the library that defines the
mode sets this variable.
See Tips for Defining, for advice about how to write the code to set up the mode's keymap variable.
It is reasonable for a major mode to rebind a key sequence with a standard meaning, if it implements a command that does “the same job” in a way that fits the major mode better. For example, a major mode for editing a programming language might redefine C-M-a to “move to the beginning of a function” in a way that works better for that language.
Major modes such as Dired or Rmail that do not allow self-insertion of text can reasonably redefine letters and other printing characters as editing commands. Dired and Rmail both do this.
-mode-syntax-table. See Syntax Tables.
-mode-abbrev-table. See Abbrev Tables.
font-lock-defaults (see Font Lock Mode).
imenu-generic-expression or
imenu-create-index-function (see Imenu).
defvar or defcustom to set mode-related variables, so
that they are not reinitialized if they already have a value. (Such
reinitialization could discard customizations made by the user.)
make-local-variable in the major mode command, not
make-variable-buffer-local. The latter function would make the
variable local to every buffer in which it is subsequently set, which
would affect buffers that do not use this mode. It is undesirable for a
mode to have such global effects. See Buffer-Local Variables.
With rare exceptions, the only reasonable way to use
make-variable-buffer-local in a Lisp package is for a variable
which is used only within that package. Using it on a variable used by
other packages would interfere with them.
-mode-hook. The major mode command should run that
hook, with run-hooks, as the very last thing it
does. See Hooks.
indented-text-mode runs text-mode-hook as
well as indented-text-mode-hook. It may run these other hooks
immediately before the mode's own hook (that is, after everything else),
or it may run them earlier.
change-major-mode-hook (see Creating Buffer-Local).
mode-class
with value special, put on as follows:
(put 'funny-mode 'mode-class 'special)
This tells Emacs that new buffers created while the current buffer is in Funny mode should not inherit Funny mode. Modes such as Dired, Rmail, and Buffer List use this feature.
auto-mode-alist to select
the mode for those file names. If you define the mode command to
autoload, you should add this element in the same file that calls
autoload. Otherwise, it is sufficient to add the element in the
file that contains the mode definition. See Auto Major Mode.
autoload form
and an example of how to add to auto-mode-alist, that users can
include in their init files (see Init File).
Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts from text-mode.el that illustrate many of the conventions listed above:
;; Create mode-specific tables. (defvar text-mode-syntax-table nil "Syntax table used while in text mode.") (if text-mode-syntax-table () ; Do not change the table if it is already set up. (setq text-mode-syntax-table (make-syntax-table)) (modify-syntax-entry ?\" ". " text-mode-syntax-table) (modify-syntax-entry ?\\ ". " text-mode-syntax-table) (modify-syntax-entry ?' "w " text-mode-syntax-table)) (defvar text-mode-abbrev-table nil "Abbrev table used while in text mode.") (define-abbrev-table 'text-mode-abbrev-table ()) (defvar text-mode-map nil ; Create a mode-specific keymap. "Keymap for Text mode. Many other modes, such as Mail mode, Outline mode and Indented Text mode, inherit all the commands defined in this map.") (if text-mode-map () ; Do not change the keymap if it is already set up. (setq text-mode-map (make-sparse-keymap)) (define-key text-mode-map "\e\t" 'ispell-complete-word) (define-key text-mode-map "\t" 'indent-relative) (define-key text-mode-map "\es" 'center-line) (define-key text-mode-map "\eS" 'center-paragraph))
Here is the complete major mode function definition for Text mode:
(defun text-mode ()
"Major mode for editing text intended for humans to read...
Special commands: \\{text-mode-map}
Turning on text-mode runs the hook `text-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map text-mode-map)
(setq local-abbrev-table text-mode-abbrev-table)
(set-syntax-table text-mode-syntax-table)
(make-local-variable 'paragraph-start)
(setq paragraph-start (concat "[ \t]*$\\|" page-delimiter))
(make-local-variable 'paragraph-separate)
(setq paragraph-separate paragraph-start)
(make-local-variable 'indent-line-function)
(setq indent-line-function 'indent-relative-maybe)
(setq mode-name "Text")
(setq major-mode 'text-mode)
(run-hooks 'text-mode-hook)) ; Finally, this permits the user to
; customize the mode with a hook.
The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) have more features than Text mode and the code is correspondingly more complicated. Here are excerpts from lisp-mode.el that illustrate how these modes are written.
;; Create mode-specific table variables.
(defvar lisp-mode-syntax-table nil "")
(defvar emacs-lisp-mode-syntax-table nil "")
(defvar lisp-mode-abbrev-table nil "")
(if (not emacs-lisp-mode-syntax-table) ; Do not change the table
; if it is already set.
(let ((i 0))
(setq emacs-lisp-mode-syntax-table (make-syntax-table))
;; Set syntax of chars up to 0 to class of chars that are
;; part of symbol names but not words.
;; (The number 0 is 48 in the ascii character set.)
(while (< i ?0)
(modify-syntax-entry i "_ " emacs-lisp-mode-syntax-table)
(setq i (1+ i)))
...
;; Set the syntax for other characters.
(modify-syntax-entry ? " " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table)
...
(modify-syntax-entry ?\( "() " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\) ")( " emacs-lisp-mode-syntax-table)
...))
;; Create an abbrev table for lisp-mode.
(define-abbrev-table 'lisp-mode-abbrev-table ())
Much code is shared among the three Lisp modes. The following function sets various variables; it is called by each of the major Lisp mode functions:
(defun lisp-mode-variables (lisp-syntax)
(cond (lisp-syntax
(set-syntax-table lisp-mode-syntax-table)))
(setq local-abbrev-table lisp-mode-abbrev-table)
...
Functions such as forward-paragraph use the value of the
paragraph-start variable. Since Lisp code is different from
ordinary text, the paragraph-start variable needs to be set
specially to handle Lisp. Also, comments are indented in a special
fashion in Lisp and the Lisp modes need their own mode-specific
comment-indent-function. The code to set these variables is the
rest of lisp-mode-variables.
(make-local-variable 'paragraph-start)
(setq paragraph-start (concat page-delimiter "\\|$" ))
(make-local-variable 'paragraph-separate)
(setq paragraph-separate paragraph-start)
...
(make-local-variable 'comment-indent-function)
(setq comment-indent-function 'lisp-comment-indent))
...
Each of the different Lisp modes has a slightly different keymap. For
example, Lisp mode binds C-c C-z to run-lisp, but the other
Lisp modes do not. However, all Lisp modes have some commands in
common. The following code sets up the common commands:
(defvar shared-lisp-mode-map ()
"Keymap for commands shared by all sorts of Lisp modes.")
(if shared-lisp-mode-map
()
(setq shared-lisp-mode-map (make-sparse-keymap))
(define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp)
(define-key shared-lisp-mode-map "\177"
'backward-delete-char-untabify))
And here is the code to set up the keymap for Lisp mode:
(defvar lisp-mode-map ()
"Keymap for ordinary Lisp mode...")
(if lisp-mode-map
()
(setq lisp-mode-map (make-sparse-keymap))
(set-keymap-parent lisp-mode-map shared-lisp-mode-map)
(define-key lisp-mode-map "\e\C-x" 'lisp-eval-defun)
(define-key lisp-mode-map "\C-c\C-z" 'run-lisp))
Finally, here is the complete major mode function definition for Lisp mode.
(defun lisp-mode ()
"Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp.
Commands:
Delete converts tabs to spaces as it moves back.
Blank lines separate paragraphs. Semicolons start comments.
\\{lisp-mode-map}
Note that `run-lisp' may be used either to start an inferior Lisp job
or to switch back to an existing one.
Entry to this mode calls the value of `lisp-mode-hook'
if that value is non-nil."
(interactive)
(kill-all-local-variables)
(use-local-map lisp-mode-map) ; Select the mode's keymap.
(setq major-mode 'lisp-mode) ; This is how describe-mode
; finds out what to describe.
(setq mode-name "Lisp") ; This goes into the mode line.
(lisp-mode-variables t) ; This defines various variables.
(setq imenu-case-fold-search t)
(set-syntax-table lisp-mode-syntax-table)
(run-hooks 'lisp-mode-hook)) ; This permits the user to use a
; hook to customize the mode.
Based on information in the file name or in the file itself, Emacs automatically selects a major mode for the new buffer when a file is visited. It also processes local variables specified in the file text.
Fundamental mode is a major mode that is not specialized for anything in particular. Other major modes are defined in effect by comparison with this one—their definitions say what to change, starting from Fundamental mode. The
fundamental-modefunction does not run any hooks; you're not supposed to customize it. (If you want Emacs to behave differently in Fundamental mode, change the global state of Emacs.)
This function establishes the proper major mode and buffer-local variable bindings for the current buffer. First it calls
set-auto-mode, then it runshack-local-variablesto parse, and bind or evaluate as appropriate, the file's local variables.If the find-file argument to
normal-modeis non-nil,normal-modeassumes that thefind-filefunction is calling it. In this case, it may process a local variables list at the end of the file and in the ‘-*-’ line. The variableenable-local-variablescontrols whether to do so. See Local Variables in Files, for the syntax of the local variables section of a file.If you run
normal-modeinteractively, the argument find-file is normallynil. In this case,normal-modeunconditionally processes any local variables list.
normal-modeusescondition-casearound the call to the major mode function, so errors are caught and reported as a ‘File mode specification error’, followed by the original error message.
This function selects the major mode that is appropriate for the current buffer. It may base its decision on the value of the ‘-*-’ line, on the visited file name (using
auto-mode-alist), on the ‘#!’ line (usinginterpreter-mode-alist), or on the file's local variables list. However, this function does not look for the ‘mode:’ local variable near the end of a file; thehack-local-variablesfunction does that. See How Major Modes are Chosen.
This variable holds the default major mode for new buffers. The standard value is
fundamental-mode.If the value of
default-major-modeisnil, Emacs uses the (previously) current buffer's major mode for the major mode of a new buffer. However, if that major mode symbol has amode-classproperty with valuespecial, then it is not used for new buffers; Fundamental mode is used instead. The modes that have this property are those such as Dired and Rmail that are useful only with text that has been specially prepared.
This function sets the major mode of buffer to the value of
default-major-mode. If that variable isnil, it uses the current buffer's major mode (if that is suitable).The low-level primitives for creating buffers do not use this function, but medium-level commands such as
switch-to-bufferandfind-file-noselectuse it whenever they create buffers.
The value of this variable determines the major mode of the initial ‘*scratch*’ buffer. The value should be a symbol that is a major mode command. The default value is
lisp-interaction-mode.
This variable contains an association list of file name patterns (regular expressions; see Regular Expressions) and corresponding major mode commands. Usually, the file name patterns test for suffixes, such as ‘.el’ and ‘.c’, but this need not be the case. An ordinary element of the alist looks like
(regexp.mode-function).For example,
(("\\`/tmp/fol/" . text-mode) ("\\.texinfo\\'" . texinfo-mode) ("\\.texi\\'" . texinfo-mode) ("\\.el\\'" . emacs-lisp-mode) ("\\.c\\'" . c-mode) ("\\.h\\'" . c-mode) ...)When you visit a file whose expanded file name (see File Name Expansion) matches a regexp,
set-auto-modecalls the corresponding mode-function. This feature enables Emacs to select the proper major mode for most files.If an element of
auto-mode-alisthas the form(regexp functiont), then after calling function, Emacs searchesauto-mode-alistagain for a match against the portion of the file name that did not match before. This feature is useful for uncompression packages: an entry of the form("\\.gz\\'"functiont)can uncompress the file and then put the uncompressed file in the proper mode according to the name sans ‘.gz’.Here is an example of how to prepend several pattern pairs to
auto-mode-alist. (You might use this sort of expression in your init file.)(setq auto-mode-alist (append ;; File name (within directory) starts with a dot. '(("/\\.[^/]*\\'" . fundamental-mode) ;; File name has no dot. ("[^\\./]*\\'" . fundamental-mode) ;; File name ends in ‘.C’. ("\\.C\\'" . c++-mode)) auto-mode-alist))
This variable specifies major modes to use for scripts that specify a command interpreter in a ‘#!’ line. Its value is a list of elements of the form
(interpreter.mode); for example,("perl" . perl-mode)is one element present by default. The element says to use mode mode if the file specifies an interpreter which matches interpreter. The value of interpreter is actually a regular expression.This variable is applicable only when the
auto-mode-alistdoes not indicate which major mode to use.
The describe-mode function is used to provide information
about major modes. It is normally called with C-h m. The
describe-mode function uses the value of major-mode,
which is why every major mode function needs to set the
major-mode variable.
This function displays the documentation of the current major mode.
The
describe-modefunction calls thedocumentationfunction using the value ofmajor-modeas an argument. Thus, it displays the documentation string of the major mode function. (See Accessing Documentation.)
This variable holds the symbol for the current buffer's major mode. This symbol should have a function definition that is the command to switch to that major mode. The
describe-modefunction uses the documentation string of the function as the documentation of the major mode.
It's often useful to define a new major mode in terms of an existing
one. An easy way to do this is to use define-derived-mode.
This construct defines variant as a major mode command, using name as the string form of the mode name.
The new command variant is defined to call the function parent, then override certain aspects of that parent mode:
- The new mode has its own keymap, named variant
-map.define-derived-modeinitializes this map to inherit from parent-map, if it is not already set.- The new mode has its own syntax table, kept in the variable variant
-syntax-table.define-derived-modeinitializes this variable by copying parent-syntax-table, if it is not already set.- The new mode has its own abbrev table, kept in the variable variant
-abbrev-table.define-derived-modeinitializes this variable by copying parent-abbrev-table, if it is not already set.- The new mode has its own mode hook, variant
-hook, which it runs in standard fashion as the very last thing that it does. (The new mode also runs the mode hook of parent as part of calling parent.)In addition, you can specify how to override other aspects of parent with body. The command variant evaluates the forms in body after setting up all its usual overrides, just before running variant
-hook.The argument docstring specifies the documentation string for the new mode. If you omit docstring,
define-derived-modegenerates a documentation string.Here is a hypothetical example:
(define-derived-mode hypertext-mode text-mode "Hypertext" "Major mode for hypertext. \\{hypertext-mode-map}" (setq case-fold-search nil)) (define-key hypertext-mode-map [down-mouse-3] 'do-hyper-link)Do not write an
interactivespec in the definition;define-derived-modedoes that automatically.
A minor mode provides features that users may enable or disable independently of the choice of major mode. Minor modes can be enabled individually or in combination. Minor modes would be better named “generally available, optional feature modes,” except that such a name would be unwieldy.
A minor mode is not usually meant as a variation of a single major mode. Usually they are general and can apply to many major modes. For example, Auto Fill mode works with any major mode that permits text insertion. To be general, a minor mode must be effectively independent of the things major modes do.
A minor mode is often much more difficult to implement than a major mode. One reason is that you should be able to activate and deactivate minor modes in any order. A minor mode should be able to have its desired effect regardless of the major mode and regardless of the other minor modes in effect.
Often the biggest problem in implementing a minor mode is finding a way to insert the necessary hook into the rest of Emacs. Minor mode keymaps make this easier than it used to be.
There are conventions for writing minor modes just as there are for major modes. Several of the major mode conventions apply to minor modes as well: those regarding the name of the mode initialization function, the names of global symbols, and the use of keymaps and other tables.
In addition, there are several conventions that are specific to minor modes.
nil to disable; anything else to
enable).
If possible, implement the mode so that setting the variable automatically enables or disables the mode. Then the minor mode command does not need to do anything except set the variable.
This variable is used in conjunction with the minor-mode-alist to
display the minor mode name in the mode line. It can also enable
or disable a minor mode keymap. Individual commands or hooks can also
check the variable's value.
If you want the minor mode to be enabled separately in each buffer, make the variable buffer-local.
The command should accept one optional argument. If the argument is
nil, it should toggle the mode (turn it on if it is off, and off
if it is on). Otherwise, it should turn the mode on if the argument is
a positive integer, a symbol other than nil or -, or a
list whose car is such an integer or symbol; it should turn the
mode off otherwise.
Here is an example taken from the definition of transient-mark-mode.
It shows the use of transient-mark-mode as a variable that enables or
disables the mode's behavior, and also shows the proper way to toggle,
enable or disable the minor mode based on the raw prefix argument value.
(setq transient-mark-mode
(if (null arg) (not transient-mark-mode)
(> (prefix-numeric-value arg) 0)))
minor-mode-alist for each minor mode
(see Mode Line Variables), if you want to indicate the minor mode in
the mode line. This element should be a list of the following form:
(mode-variable string)
Here mode-variable is the variable that controls enabling of the minor mode, and string is a short string, starting with a space, to represent the mode in the mode line. These strings must be short so that there is room for several of them at once.
When you add an element to minor-mode-alist, use assq to
check for an existing element, to avoid duplication. For example:
(unless (assq 'leif-mode minor-mode-alist)
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist)))
or like this, using add-to-list (see Setting Variables):
(add-to-list 'minor-mode-alist '(leif-mode " Leif"))
Global minor modes distributed with Emacs should if possible support
enabling and disabling via Custom (see Customization). To do this,
the first step is to define the mode variable with defcustom, and
specify :type boolean.
If just setting the variable is not sufficient to enable the mode, you
should also specify a :set method which enables the mode by
invoke the mode command. Note in the variable's documentation string that
setting the variable other than via Custom may not take effect.
Also mark the definition with an autoload cookie (see Autoload),
and specify a :require so that customizing the variable will load
the library that defines the mode. This will copy suitable definitions
into loaddefs.el so that users can use customize-option to
enable the mode. For example:
;;;###autoload
(defcustom msb-mode nil
"Toggle msb-mode.
Setting this variable directly does not take effect;
use either \\[customize] or the function `msb-mode'."
:set (lambda (symbol value)
(msb-mode (or value 0)))
:initialize 'custom-initialize-default
:version "20.4"
:type 'boolean
:group 'msb
:require 'msb)
Each minor mode can have its own keymap, which is active when the mode
is enabled. To set up a keymap for a minor mode, add an element to the
alist minor-mode-map-alist. See Active Keymaps.
One use of minor mode keymaps is to modify the behavior of certain
self-inserting characters so that they do something else as well as
self-insert. In general, this is the only way to do that, since the
facilities for customizing self-insert-command are limited to
special cases (designed for abbrevs and Auto Fill mode). (Do not try
substituting your own definition of self-insert-command for the
standard one. The editor command loop handles this function specially.)
The key sequences bound in a minor mode should consist of C-c followed by a punctuation character other than {, }, <, >, :, and ;. (Those few punctuation characters are reserved for major modes.)
The macro define-minor-mode offers a convenient way of
implementing a mode in one self-contained definition. It supports only
buffer-local minor modes, not global ones.
This macro defines a new minor mode whose name is mode (a symbol). It defines a command named mode to toggle the minor mode, with doc as its documentation string. It also defines a variable named mode, which is set to
tornilby enabling or disabling the mode. The variable is initialized to init-value.The command named mode finishes by executing the body forms, if any, after it has performed the standard actions such as setting the variable named mode.
The string mode-indicator says what to display in the mode line when the mode is enabled; if it is
nil, the mode is not displayed in the mode line.The optional argument keymap specifies the keymap for the minor mode. It can be a variable name, whose value is the keymap, or it can be an alist specifying bindings in this form:
(key-sequence . definition)
Here is an example of using define-minor-mode:
(define-minor-mode hungry-mode
"Toggle Hungry mode.
With no argument, this command toggles the mode.
Non-null prefix argument turns on the mode.
Null prefix argument turns off the mode.
When Hungry mode is enabled, the control delete key
gobbles all preceding whitespace except the last.
See the command \\[hungry-electric-delete]."
;; The initial value.
nil
;; The indicator for the mode line.
" Hungry"
;; The minor mode bindings.
'(("\C-\^?" . hungry-electric-delete)
("\C-\M-\^?"
. (lambda ()
(interactive)
(hungry-electric-delete t)))))
This defines a minor mode named “Hungry mode”, a command named
hungry-mode to toggle it, a variable named hungry-mode
which indicates whether the mode is enabled, and a variable named
hungry-mode-map which holds the keymap that is active when the
mode is enabled. It initializes the keymap with key bindings for
C-<DEL> and C-M-<DEL>.
The name easy-mmode-define-minor-mode is an alias
for this macro.
Each Emacs window (aside from minibuffer windows) typically has a mode line at the bottom, which displays status information about the buffer displayed in the window. The mode line contains information about the buffer, such as its name, associated file, depth of recursive editing, and major and minor modes. A window can also have a header line, which is much like the mode line but appears at the top of the window (starting in Emacs 21).
This section describes how to control the contents of the mode line and header line. We include it in this chapter because much of the information displayed in the mode line relates to the enabled major and minor modes.
mode-line-format is a buffer-local variable that holds a
template used to display the mode line of the current buffer. All
windows for the same buffer use the same mode-line-format, so
their mode lines appear the same—except for scrolling percentages, and
line and column numbers, since those depend on point and on how the
window is scrolled. header-line-format is used likewise for
header lines.
The mode line and header line of a window are normally updated
whenever a different buffer is shown in the window, or when the buffer's
modified-status changes from nil to t or vice-versa. If
you modify any of the variables referenced by mode-line-format
(see Mode Line Variables), or any other variables and data
structures that affect how text is displayed (see Display), you may
want to force an update of the mode line so as to display the new
information or display it in the new way.
Force redisplay of the current buffer's mode line and header line.
The mode line is usually displayed in inverse video; see
mode-line-inverse-video in Inverse Video.
The mode line contents are controlled by a data structure of lists, strings, symbols, and numbers kept in buffer-local variables. The data structure is called a mode line construct, and it is built in recursive fashion out of simpler mode line constructs. The same data structure is used for constructing frame titles (see Frame Titles) and header lines (see Header Lines).
The value of this variable is a mode line construct with overall responsibility for the mode line format. The value of this variable controls which other variables are used to form the mode line text, and where they appear.
If you set this variable to
nilin a buffer, that buffer does not have a mode line. (This feature was added in Emacs 21.)
A mode line construct may be as simple as a fixed string of text, but it usually specifies how to use other variables to construct the text. Many of these variables are themselves defined to have mode line constructs as their values.
The default value of mode-line-format incorporates the values
of variables such as mode-name and minor-mode-alist.
Because of this, very few modes need to alter mode-line-format
itself. For most purposes, it is sufficient to alter some of the
variables that mode-line-format refers to.
A mode line construct may be a list, a symbol, or a string. If the value is a list, each element may be a list, a symbol, or a string.
The mode line can display various faces, if the strings that control
it have the face property. See Properties in Mode. In
addition, the face mode-line is used as a default for the whole
mode line (see Standard Faces).
%-constructs. Decimal digits after the ‘%’
specify the field width for space filling on the right (i.e., the data
is left justified). See %-Constructs.
t and nil are ignored, as is any
symbol whose value is void.
There is one exception: if the value of symbol is a string, it is
displayed verbatim: the %-constructs are not recognized.
(string rest...) or (list rest...)(:eval form):eval says to evaluate
form, and use the result as a string to display.
(This feature is new as of Emacs 21.)
(symbol then else)nil, the second element, then, is processed
recursively as a mode line element. But if the value of symbol is
nil, the third element, else, is processed recursively.
You may omit else; then the mode line element displays nothing if
the value of symbol is nil.
(width rest...)For example, the usual way to show what percentage of a buffer is above
the top of the window is to use a list like this: (-3 "%p").
If you do alter mode-line-format itself, the new value should
use the same variables that appear in the default value (see Mode Line Variables), rather than duplicating their contents or displaying
the information in another fashion. This way, customizations made by
the user or by Lisp programs (such as display-time and major
modes) via changes to those variables remain effective.
Here is an example of a mode-line-format that might be
useful for shell-mode, since it contains the host name and default
directory.
(setq mode-line-format
(list "-"
'mode-line-mule-info
'mode-line-modified
'mode-line-frame-identification
"%b--"
;; Note that this is evaluated while making the list.
;; It makes a mode line construct which is just a string.
(getenv "HOST")
":"
'default-directory
" "
'global-mode-string
" %[("
'(:eval (mode-line-mode-name))
'mode-line-process
'minor-mode-alist
"%n"
")%]--"
'(which-func-mode ("" which-func-format "--"))
'(line-number-mode "L%l--")
'(column-number-mode "C%c--")
'(-3 . "%p")
"-%-"))
(The variables line-number-mode, column-number-mode
and which-func-mode enable particular minor modes; as usual,
these variable names are also the minor mode command names.)
This section describes variables incorporated by the
standard value of mode-line-format into the text of the mode
line. There is nothing inherently special about these variables; any
other variables could have the same effects on the mode line if
mode-line-format were changed to use them.
This variable holds the value of the mode-line construct that displays information about the language environment, buffer coding system, and current input method. See Non-ASCII Characters.
This variable holds the value of the mode-line construct that displays whether the current buffer is modified.
The default value of
mode-line-modifiedis("%1*%1+"). This means that the mode line displays ‘**’ if the buffer is modified, ‘--’ if the buffer is not modified, ‘%%’ if the buffer is read only, and ‘%*’ if the buffer is read only and modified.Changing this variable does not force an update of the mode line.
This variable identifies the current frame. The default value is
" "if you are using a window system which can show multiple frames, or"-%F "on an ordinary terminal which shows only one frame at a time.
This variable identifies the buffer being displayed in the window. Its default value is
("%12b"), which displays the buffer name, padded with spaces to at least 12 columns.
This variable holds a mode line spec that appears in the mode line by default, just after the buffer name. The command
display-timesetsglobal-mode-stringto refer to the variabledisplay-time-string, which holds a string containing the time and load information.The ‘%M’ construct substitutes the value of
global-mode-string, but that is obsolete, since the variable is included in the mode line frommode-line-format.
This buffer-local variable holds the “pretty” name of the current buffer's major mode. Each major mode should set this variable so that the mode name will appear in the mode line.
This variable holds an association list whose elements specify how the mode line should indicate that a minor mode is active. Each element of the
minor-mode-alistshould be a two-element list:(minor-mode-variable mode-line-string)More generally, mode-line-string can be any mode line spec. It appears in the mode line when the value of minor-mode-variable is non-
nil, and not otherwise. These strings should begin with spaces so that they don't run together. Conventionally, the minor-mode-variable for a specific mode is set to a non-nilvalue when that minor mode is activated.The default value of
minor-mode-alistis:minor-mode-alist => ((vc-mode vc-mode) (abbrev-mode " Abbrev") (overwrite-mode overwrite-mode) (auto-fill-function " Fill") (defining-kbd-macro " Def") (isearch-mode isearch-mode))
minor-mode-alistitself is not buffer-local. Each variable mentioned in the alist should be buffer-local if its minor mode can be enabled separately in each buffer.
This buffer-local variable contains the mode line information on process status in modes used for communicating with subprocesses. It is displayed immediately following the major mode name, with no intervening space. For example, its value in the ‘*shell*’ buffer is
(":%s"), which allows the shell to display its status along with the major mode as: ‘(Shell:run)’. Normally this variable isnil.
Some variables are used by minor-mode-alist to display
a string for various minor modes when enabled. This is a typical
example:
The variable
vc-mode, buffer-local in each buffer, records whether the buffer's visited file is maintained with version control, and, if so, which kind. Its value is a string that appears in the mode line, ornilfor no version control.
The variable default-mode-line-format is where
mode-line-format usually gets its value:
This variable holds the default
mode-line-formatfor buffers that do not override it. This is the same as(default-value 'mode-line-format).The default value of
default-mode-line-formatis this list:("-" mode-line-mule-info mode-line-modified mode-line-frame-identification mode-line-buffer-identification " " global-mode-string " %[(" ;;mode-line-mode-nameis a function ;; that copies the mode name and adds text ;; properties to make it mouse-sensitive. (:eval (mode-line-mode-name)) mode-line-process minor-mode-alist "%n" ")%]--" (which-func-mode ("" which-func-format "--")) (line-number-mode "L%l--") (column-number-mode "C%c--") (-3 . "%p") "-%-")
%-Constructs in the Mode LineThe following table lists the recognized %-constructs and what
they mean. In any construct except ‘%%’, you can add a decimal
integer after the ‘%’ to specify how many characters to display.
%bbuffer-name function.
See Buffer Names.
%c%fbuffer-file-name
function. See Buffer File Name.
%F%l%nnarrow-to-region in Narrowing).
%p%P%sprocess-status. See Process Information.
%t%*buffer-read-only); buffer-modified-p); %+buffer-modified-p); buffer-read-only); %&%[%]%-%%%-constructs are allowed.
The following two %-constructs are still supported, but they are
obsolete, since you can get the same results with the variables
mode-name and global-mode-string.
%mmode-name.
%Mglobal-mode-string. Currently, only
display-time modifies the value of global-mode-string.
Starting in Emacs 21, certain text properties are meaningful in the
mode line. The face property affects the appearance of text; the
help-echo property associate help strings with the text, and
local-map can make the text mouse-sensitive.
There are three ways to specify text properties for text in the mode line:
local-map property directly into the
mode-line data structure.
local-map property on a mode-line %-construct
such as ‘%12b’; then the expansion of the %-construct
will have that same text property.
:eval form in the mode-line data
structure, and make form evaluate to a string that has a
local-map property.
You use the local-map property to specify a keymap. Like any
keymap, it can bind character keys and function keys; but that has no
effect, since it is impossible to move point into the mode line. This
keymap can only take real effect for mouse clicks.
Starting in Emacs 21, a window can have a header line at the top, just as it can have a mode line at the bottom. The header line feature works just like the mode line feature, except that it's controlled by different variables.
This variable, local in every buffer, specifies how to display the header line, for windows displaying the buffer. The format of the value is the same as for
mode-line-format(see Mode Line Data).
This variable holds the default
header-line-formatfor buffers that do not override it. This is the same as(default-value 'header-line-format).It is normally
nil, so that ordinary buffers have no header line.
Imenu is a feature that lets users select a definition or section in the buffer, from a menu which lists all of them, to go directly to that location in the buffer. Imenu works by constructing a buffer index which lists the names and buffer positions of the definitions, or other named portions of the buffer; then the user can choose one of them and move point to it. This section explains how to customize how Imenu finds the definitions or buffer portions for a particular major mode.
The usual and simplest way is to set the variable
imenu-generic-expression:
This variable, if non-
nil, specifies regular expressions for finding definitions for Imenu. In the simplest case, elements should look like this:(menu-title regexp subexp)Here, if menu-title is non-
nil, it says that the matches for this element should go in a submenu of the buffer index; menu-title itself specifies the name for the submenu. If menu-title isnil, the matches for this element go directly in the top level of the buffer index.The second item in the list, regexp, is a regular expression (see Regular Expressions); anything in the buffer that it matches is considered a definition, something to mention in the buffer index. The third item, subexp, indicates which subexpression in regexp matches the definition's name.
An element can also look like this:
(menu-title regexp index function arguments...)Each match for this element creates a special index item which, if selected by the user, calls function with arguments consisting of the item name, the buffer position, and arguments.
For Emacs Lisp mode, pattern could look like this:
((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2) ("*Vars*" "^\\s-*(def\\(var\\|const\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2) ("*Types*" "^\\s-*\ (def\\(type\\|struct\\|class\\|ine-condition\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2))Setting this variable makes it buffer-local in the current buffer.
This variable controls whether matching against imenu-generic-expression is case-sensitive:
t, the default, means matching should ignore case.Setting this variable makes it buffer-local in the current buffer.
This variable is an alist of syntax table modifiers to use while processing
imenu-generic-expression, to override the syntax table of the current buffer. Each element should have this form:(characters . syntax-description)The car, characters, can be either a character or a string. The element says to give that character or characters the syntax specified by syntax-description, which is passed to
modify-syntax-entry(see Syntax Table Functions).This feature is typically used to give word syntax to characters which normally have symbol syntax, and thus to simplify
imenu-generic-expressionand speed up matching. For example, Fortran mode uses it this way:(setq imenu-syntax-alist '(("_$" . "w")))The
imenu-generic-expressionpatterns can then use ‘\\sw+’ instead of ‘\\(\\sw\\|\\s_\\)+’. Note that this technique may be inconvenient when the mode needs to limit the initial character of a name to a smaller set of characters than are allowed in the rest of a name.Setting this variable makes it buffer-local in the current buffer.
Another way to customize Imenu for a major mode is to set the
variables imenu-prev-index-position-function and
imenu-extract-index-name-function:
If this variable is non-
nil, its value should be a function that finds the next “definition” to put in the buffer index, scanning backward in the buffer from point. It should returnnilif it doesn't find another “definition” before point. Otherwise it shuould leave point at the place it finds a “definition,” and return any non-nilvalue.Setting this variable makes it buffer-local in the current buffer.
If this variable is non-
nil, its value should be a function to return the name for a definition, assuming point is in that definition as theimenu-prev-index-position-functionfunction would leave it.Setting this variable makes it buffer-local in the current buffer.
The last way to customize Imenu for a major mode is to set the
variable imenu-create-index-function:
This variable specifies the function to use for creating a buffer index. The function should take no arguments, and return an index for the current buffer. It is called within
save-excursion, so where it leaves point makes no difference.The default value is a function that uses
imenu-generic-expressionto produce the index alist. If you specify a different function, thenimenu-generic-expressionis not used.Setting this variable makes it buffer-local in the current buffer.
This variable holds the index alist for the current buffer. Setting it makes it buffer-local in the current buffer.
Simple elements in the alist look like
(index-name.index-position). Selecting a simple element has the effect of moving to position index-position in the buffer.Special elements look like
(index-name position function arguments...). Selecting a special element performs(funcall function index-name position arguments...)A nested sub-alist element looks like
(index-name sub-alist).
Font Lock mode is a feature that automatically attaches
face properties to certain parts of the buffer based on their
syntactic role. How it parses the buffer depends on the major mode;
most major modes define syntactic criteria for which faces to use in
which contexts. This section explains how to customize Font Lock for a
particular major mode.
Font Lock mode finds text to highlight in two ways: through syntactic
parsing based on the syntax table, and through searching (usually for
regular expressions). Syntactic fontification happens first; it finds
comments and string constants, and highlights them using
font-lock-comment-face and font-lock-string-face
(see Faces for Font Lock). Search-based fontification follows.
There are several variables that control how Font Lock mode highlights
text. But major modes should not set any of these variables directly.
Instead, they should set font-lock-defaults as a buffer-local
variable. The value assigned to this variable is used, if and when Font
Lock mode is enabled, to set all the other variables.
This variable is set by major modes, as a buffer-local variable, to specify how to fontify text in that mode. The value should look like this:
(keywords keywords-only case-fold syntax-alist syntax-begin other-vars...)The first element, keywords, indirectly specifies the value of
font-lock-keywords. It can be a symbol, a variable whose value is the list to use forfont-lock-keywords. It can also be a list of several such symbols, one for each possible level of fontification. The first symbol specifies how to do level 1 fontification, the second symbol how to do level 2, and so on.The second element, keywords-only, specifies the value of the variable
font-lock-keywords-only. If this is non-nil, syntactic fontification (of strings and comments) is not performed.The third element, case-fold, specifies the value of
font-lock-case-fold-search. If it is non-nil, Font Lock mode ignores case when searching as directed byfont-lock-keywords.If the fourth element, syntax-alist, is non-
nil, it should be a list of cons cells of the form(char-or-string.string). These are used to set up a syntax table for fontification (see Syntax Table Functions). The resulting syntax table is stored infont-lock-syntax-table.The fifth element, syntax-begin, specifies the value of
font-lock-beginning-of-syntax-function(see below).All the remaining elements (if any) are collectively called other-vars. Each of these elements should have the form
(variable.value)—which means, make variable buffer-local and then set it to value. You can use these other-vars to set other variables that affect fontification, aside from those you can control with the first five elements.
The most important variable for customizing Font Lock mode is
font-lock-keywords. It specifies the search criteria for
search-based fontification.
This variable's value is a list of the keywords to highlight. Be careful when composing regular expressions for this list; a poorly written pattern can dramatically slow things down!
Each element of font-lock-keywords specifies how to find
certain cases of text, and how to highlight those cases. Font Lock mode
processes the elements of font-lock-keywords one by one, and for
each element, it finds and handles all matches. Ordinarily, once
part of the text has been fontified already, this cannot be overridden
by a subsequent match in the same text; but you can specify different
behavior using the override element of a highlighter.
Each element of font-lock-keywords should have one of these
forms:
font-lock-keyword-face. For example,
;; Highlight discrete occurrences of ‘foo’
;; using font-lock-keyword-face.
"\\<foo\\>"
The function regexp-opt (see Syntax of Regexps) is useful for
calculating optimal regular expressions to match a number of different
keywords.
font-lock-keyword-face.
When function is called, it receives one argument, the limit of
the search. It should return non-nil if it succeeds, and set the
match data to describe the match that was found.
(matcher . match) ;; Highlight the ‘bar’ in each occurrence of ‘fubar’,
;; using font-lock-keyword-face.
("fu\\(bar\\)" . 1)
If you use regexp-opt to produce the regular expression
matcher, then you can use regexp-opt-depth (see Syntax of Regexps) to calculate the value for match.
(matcher . facename) ;; Highlight occurrences of ‘fubar’,
;; using the face which is the value of fubar-face.
("fubar" . fubar-face)
(matcher . highlighter) (subexp facename override laxmatch)
The car, subexp, is an integer specifying which subexpression of the match to fontify (0 means the entire matching text). The second subelement, facename, specifies the face, as described above.
The last two values in highlighter, override and
laxmatch, are flags. If override is t, this element
can override existing fontification made by previous elements of
font-lock-keywords. If it is keep, then each character is
fontified if it has not been fontified already by some other element.
If it is prepend, the face facename is added to the
beginning of the face property. If it is append, the face
facename is added to the end of the face property.
If laxmatch is non-nil, it means there should be no error
if there is no subexpression numbered subexp in matcher.
Obviously, fontification of the subexpression numbered subexp will
not occur. However, fontification of other subexpressions (and other
regexps) will continue. If laxmatch is nil, and the
specified subexpression is missing, then an error is signalled which
terminates search-based fontification.
Here are some examples of elements of this kind, and what they do:
;; Highlight occurrences of either ‘foo’ or ‘bar’, ;; usingfoo-bar-face, even if they have already been highlighted. ;;foo-bar-faceshould be a variable whose value is a face. ("foo\\|bar" 0 foo-bar-face t) ;; Highlight the first subexpression within each occurrence ;; that the functionfubar-matchfinds, ;; using the face which is the value offubar-face. (fubar-match 1 fubar-face)
(matcher highlighters...)(eval . form)font-lock-keywords is used in a buffer.
Its value should have one of the forms described in this table.
Warning: Do not design an element of font-lock-keywords
to match text which spans lines; this does not work reliably. While
font-lock-fontify-buffer handles multi-line patterns correctly,
updating when you edit the buffer does not, since it considers text one
line at a time.
This section describes additional variables that a major mode
can set by means of font-lock-defaults.
Non-
nilmeans Font Lock should not fontify comments or strings syntactically; it should only fontify based onfont-lock-keywords.
Non-
nilmeans that regular expression matching for the sake offont-lock-keywordsshould be case-insensitive.
This variable specifies the syntax table to use for fontification of comments and strings.
If this variable is non-
nil, it should be a function to move point back to a position that is syntactically at “top level” and outside of strings or comments. Font Lock uses this when necessary to get the right results for syntactic fontification.This function is called with no arguments. It should leave point at the beginning of any enclosing syntactic block. Typical values are
beginning-of-line(i.e., the start of the line is known to be outside a syntactic block), orbeginning-of-defunfor programming modes orbackward-paragraphfor textual modes (i.e., the mode-dependent function is known to move outside a syntactic block).If the value is
nil, the beginning of the buffer is used as a position outside of a syntactic block. This cannot be wrong, but it can be slow.
If this variable is non-
nil, it should be a function that is called with no arguments, to choose an enclosing range of text for refontification for the command M-g M-g (font-lock-fontify-block).The function should report its choice by placing the region around it. A good choice is a range of text large enough to give proper results, but not too large so that refontification becomes slow. Typical values are
mark-defunfor programming modes ormark-paragraphfor textual modes.
Many major modes offer three different levels of fontification. You
can define multiple levels by using a list of symbols for keywords
in font-lock-defaults. Each symbol specifies one level of
fontification; it is up to the user to choose one of these levels. The
chosen level's symbol value is used to initialize
font-lock-keywords.
Here are the conventions for how to define the levels of fontification:
You can make Font Lock mode use any face, but several faces are
defined specifically for Font Lock mode. Each of these symbols is both
a face name, and a variable whose default value is the symbol itself.
Thus, the default value of font-lock-comment-face is
font-lock-comment-face. This means you can write
font-lock-comment-face in a context such as
font-lock-keywords where a face-name-valued expression is used.
font-lock-comment-facefont-lock-string-facefont-lock-keyword-facefor and if in C.
font-lock-builtin-facefont-lock-function-name-facefont-lock-variable-name-facefont-lock-type-facefont-lock-constant-facefont-lock-warning-face#error
directives in C.
Font Lock mode can be used to update syntax-table properties
automatically. This is useful in languages for which a single syntax
table by itself is not sufficient.
This variable enables and controls syntactic Font Lock. Its value should be a list of elements of this form:
(matcher subexp syntax override laxmatch)The parts of this element have the same meanings as in the corresponding sort of element of
font-lock-keywords,(matcher subexp facename override laxmatch)However, instead of specifying the value facename to use for the
faceproperty, it specifies the value syntax to use for thesyntax-tableproperty. Here, syntax can be a variable whose value is a syntax table, a syntax entry of the form(syntax-code.matching-char), or an expression whose value is one of those two types.
A hook is a variable where you can store a function or functions to be called on a particular occasion by an existing program. Emacs provides hooks for the sake of customization. Most often, hooks are set up in the init file (see Init File), but Lisp programs can set them also. See Standard Hooks, for a list of standard hook variables.
Most of the hooks in Emacs are normal hooks. These variables contain lists of functions to be called with no arguments. When the hook name ends in ‘-hook’, that tells you it is normal. We try to make all hooks normal, as much as possible, so that you can use them in a uniform way.
Every major mode function is supposed to run a normal hook called the
mode hook as the last step of initialization. This makes it easy
for a user to customize the behavior of the mode, by overriding the
buffer-local variable assignments already made by the mode. But hooks
are used in other contexts too. For example, the hook
suspend-hook runs just before Emacs suspends itself
(see Suspending Emacs).
The recommended way to add a hook function to a normal hook is by
calling add-hook (see below). The hook functions may be any of
the valid kinds of functions that funcall accepts (see What Is a Function). Most normal hook variables are initially void;
add-hook knows how to deal with this.
If the hook variable's name does not end with ‘-hook’, that indicates it is probably an abnormal hook. Then you should look at its documentation to see how to use the hook properly.
If the variable's name ends in ‘-functions’ or ‘-hooks’,
then the value is a list of functions, but it is abnormal in that either
these functions are called with arguments or their values are used in
some way. You can use add-hook to add a function to the list,
but you must take care in writing the function. (A few of these
variables are actually normal hooks which were named before we
established the convention of using ‘-hook’ for them.)
If the variable's name ends in ‘-function’, then its value is just a single function, not a list of functions.
Here's an example that uses a mode hook to turn on Auto Fill mode when in Lisp Interaction mode:
(add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)
At the appropriate time, Emacs uses the run-hooks function to
run particular hooks. This function calls the hook functions that have
been added with add-hook.
This function takes one or more hook variable names as arguments, and runs each hook in turn. Each argument should be a symbol that is a hook variable. These arguments are processed in the order specified.
If a hook variable has a non-
nilvalue, that value may be a function or a list of functions. If the value is a function (either a lambda expression or a symbol with a function definition), it is called. If it is a list, the elements are called, in order. The hook functions are called with no arguments. Nowadays, storing a single function in the hook variable is semi-obsolete; you should always use a list of functions.For example, here's how
emacs-lisp-moderuns its mode hook:(run-hooks 'emacs-lisp-mode-hook)
This function is the way to run an abnormal hook which passes arguments to the hook functions. It calls each of the hook functions, passing each of them the arguments args.
This function is the way to run an abnormal hook which passes arguments to the hook functions, and stops as soon as any hook function fails. It calls each of the hook functions, passing each of them the arguments args, until some hook function returns
nil. Then it stops, and returnsnilif some hook function returnednil. Otherwise it returns a non-nilvalue.
This function is the way to run an abnormal hook which passes arguments to the hook functions, and stops as soon as any hook function succeeds. It calls each of the hook functions, passing each of them the arguments args, until some hook function returns non-
nil. Then it stops, and returns whatever was returned by the last hook function that was called.
This function is the handy way to add function function to hook variable hook. The argument function may be any valid Lisp function with the proper number of arguments. For example,
(add-hook 'text-mode-hook 'my-text-hook-function)adds
my-text-hook-functionto the hook calledtext-mode-hook.You can use
add-hookfor abnormal hooks as well as for normal hooks.It is best to design your hook functions so that the order in which they are executed does not matter. Any dependence on the order is “asking for trouble.” However, the order is predictable: normally, function goes at the front of the hook list, so it will be executed first (barring another
add-hookcall). If the optional argument append is non-nil, the new hook function goes at the end of the hook list and will be executed last.If local is non-
nil, that says to make the new hook function buffer-local in the current buffer and automatically callsmake-local-hookto make the hook itself buffer-local.
This function removes function from the hook variable hook.
If local is non-
nil, that says to remove function from the buffer-local hook list instead of from the global hook list. If the hook variable itself is not buffer-local, then the value of local makes no difference.
This function makes the hook variable
hookbuffer-local in the current buffer. When a hook variable is buffer-local, it can have buffer-local and global hook functions, andrun-hooksruns all of them.This function works by adding
tas an element of the buffer-local value. That serves as a flag to use the hook functions listed in the default value of the hook variable, as well as those listed in the buffer-local value. Sincerun-hooksunderstands this flag,make-local-hookworks with all normal hooks. It works for only some non-normal hooks—those whose callers have been updated to understand this meaning oft.Do not use
make-local-variabledirectly for hook variables; it is not sufficient.
GNU Emacs Lisp has convenient on-line help facilities, most of which derive their information from the documentation strings associated with functions and variables. This chapter describes how to write good documentation strings for your Lisp programs, as well as how to write programs to access documentation.
Note that the documentation strings for Emacs are not the same thing as the Emacs manual. Manuals have their own source files, written in the Texinfo language; documentation strings are specified in the definitions of the functions and variables they apply to. A collection of documentation strings is not sufficient as a manual because a good manual is not organized in that fashion; it is organized in terms of topics of discussion.
A documentation string is written using the Lisp syntax for strings, with double-quote characters surrounding the text of the string. This is because it really is a Lisp string object. The string serves as documentation when it is written in the proper place in the definition of a function or variable. In a function definition, the documentation string follows the argument list. In a variable definition, the documentation string follows the initial value of the variable.
When you write a documentation string, make the first line a complete
sentence (or two complete sentences) since some commands, such as
apropos, show only the first line of a multi-line documentation
string. Also, you should not indent the second line of a documentation
string, if it has one, because that looks odd when you use C-h f
(describe-function) or C-h v (describe-variable) to
view the documentation string. See Documentation Tips.
Documentation strings can contain several special substrings, which stand for key bindings to be looked up in the current keymaps when the documentation is displayed. This allows documentation strings to refer to the keys for related commands and be accurate even when a user rearranges the key bindings. (See Accessing Documentation.)
In Emacs Lisp, a documentation string is accessible through the function or variable that it describes:
documentation
knows how to extract it.
variable-documentation. The
function documentation-property knows how to retrieve it.
To save space, the documentation for preloaded functions and variables (including primitive functions and autoloaded functions) is stored in the file emacs/etc/DOC-version—not inside Emacs. The documentation strings for functions and variables loaded during the Emacs session from byte-compiled files are stored in those files (see Docs and Compilation).
The data structure inside Emacs has an integer offset into the file, or
a list containing a file name and an integer, in place of the
documentation string. The functions documentation and
documentation-property use that information to fetch the
documentation string from the appropriate file; this is transparent to
the user.
For information on the uses of documentation strings, see Help.
The emacs/lib-src directory contains two utilities that you can use to print nice-looking hardcopy for the file emacs/etc/DOC-version. These are sorted-doc and digest-doc.
This function returns the documentation string that is recorded in symbol's property list under property property. It retrieves the text from a file if the value calls for that. If the property value isn't
nil, isn't a string, and doesn't refer to text in a file, then it is evaluated to obtain a string.Finally,
documentation-propertypasses the string throughsubstitute-command-keysto substitute actual key bindings, unless verbatim is non-nil.(documentation-property 'command-line-processed 'variable-documentation) => "Non-nil once command line has been processed" (symbol-plist 'command-line-processed) => (variable-documentation 188902)
This function returns the documentation string of function.
If function is a symbol, this function first looks for the
function-documentationproperty of that symbol; if that has a non-nilvalue, the documentation comes from that value (if the value is not a string, it is evaluated). If function is not a symbol, or if it has nofunction-documentationproperty, thendocumentationextracts the documentation string from the actual function definition, reading it from a file if called for.Finally, unless verbatim is non-
nil, it callssubstitute-command-keysso as to return a value containing the actual (current) key bindings.The function
documentationsignals avoid-functionerror if function has no function definition. However, it is OK if the function definition has no documentation string. In that case,documentationreturnsnil.
Here is an example of using the two functions, documentation and
documentation-property, to display the documentation strings for
several symbols in a ‘*Help*’ buffer.
(defun describe-symbols (pattern)
"Describe the Emacs Lisp symbols matching PATTERN.
All symbols that have PATTERN in their name are described
in the `*Help*' buffer."
(interactive "sDescribe symbols matching: ")
(let ((describe-func
(function
(lambda (s)
;; Print description of symbol.
(if (fboundp s) ; It is a function.
(princ
(format "%s\t%s\n%s\n\n" s
(if (commandp s)
(let ((keys (where-is-internal s)))
(if keys
(concat
"Keys: "
(mapconcat 'key-description
keys " "))
"Keys: none"))
"Function")
(or (documentation s)
"not documented"))))
(if (boundp s) ; It is a variable.
(princ
(format "%s\t%s\n%s\n\n" s
(if (user-variable-p s)
"Option " "Variable")
(or (documentation-property
s 'variable-documentation)
"not documented")))))))
sym-list)
;; Build a list of symbols that match pattern.
(mapatoms (function
(lambda (sym)
(if (string-match pattern (symbol-name sym))
(setq sym-list (cons sym sym-list))))))
;; Display the data.
(with-output-to-temp-buffer "*Help*"
(mapcar describe-func (sort sym-list 'string<))
(print-help-return-message))))
The describe-symbols function works like apropos,
but provides more information.
(describe-symbols "goal")
---------- Buffer: *Help* ----------
goal-column Option
*Semipermanent goal column for vertical motion, as set by ...
set-goal-column Keys: C-x C-n
Set the current horizontal position as a goal for C-n and C-p.
Those commands will move to this position in the line moved to
rather than trying to keep the same horizontal position.
With a non-nil argument, clears out the goal column
so that C-n and C-p resume vertical motion.
The goal column is stored in the variable `goal-column'.
temporary-goal-column Variable
Current goal column for vertical motion.
It is the column where point was
at the start of current run of vertical motion commands.
When the `track-eol' feature is doing its job, the value is 9999.
---------- Buffer: *Help* ----------
The asterisk ‘*’ as the first character of a variable's doc string,
as shown above for the goal-column variable, means that it is a
user option; see the description of defvar in Defining Variables.
This function is used only during Emacs initialization, just before the runnable Emacs is dumped. It finds the file offsets of the documentation strings stored in the file filename, and records them in the in-core function definitions and variable property lists in place of the actual strings. See Building Emacs.
Emacs reads the file filename from the emacs/etc directory. When the dumped Emacs is later executed, the same file will be looked for in the directory
doc-directory. Usually filename is"DOC-version".
This variable holds the name of the directory which should contain the file
"DOC-version"that contains documentation strings for built-in and preloaded functions and variables.In most cases, this is the same as
data-directory. They may be different when you run Emacs from the directory where you built it, without actually installing it. Seedata-directoryin Help Functions.In older Emacs versions,
exec-directorywas used for this.
When documentation strings refer to key sequences, they should use the
current, actual key bindings. They can do so using certain special text
sequences described below. Accessing documentation strings in the usual
way substitutes current key binding information for these special
sequences. This works by calling substitute-command-keys. You
can also call that function yourself.
Here is a list of the special sequences and what they mean:
\[command]\{mapvar}describe-bindings.
\<mapvar>\=Please note: Each ‘\’ must be doubled when written in a string in Emacs Lisp.
This function scans string for the above special sequences and replaces them by what they stand for, returning the result as a string. This permits display of documentation that refers accurately to the user's own customized key bindings.
Here are examples of the special sequences:
(substitute-command-keys
"To abort recursive edit, type: \\[abort-recursive-edit]")
=> "To abort recursive edit, type: C-]"
(substitute-command-keys
"The keys that are defined for the minibuffer here are:
\\{minibuffer-local-must-match-map}")
=> "The keys that are defined for the minibuffer here are:
? minibuffer-completion-help
SPC minibuffer-complete-word
TAB minibuffer-complete
C-j minibuffer-complete-and-exit
RET minibuffer-complete-and-exit
C-g abort-recursive-edit
"
(substitute-command-keys
"To abort a recursive edit from the minibuffer, type\
\\<minibuffer-local-must-match-map>\\[abort-recursive-edit].")
=> "To abort a recursive edit from the minibuffer, type C-g."
These functions convert events, key sequences, or characters to textual descriptions. These descriptions are useful for including arbitrary text characters or key sequences in messages, because they convert non-printing and whitespace characters to sequences of printing characters. The description of a non-whitespace printing character is the character itself.
This function returns a string containing the Emacs standard notation for the input events in sequence. The argument sequence may be a string, vector or list. See Input Events, for more information about valid events. See also the examples for
single-key-description, below.
This function returns a string describing event in the standard Emacs notation for keyboard input. A normal printing character appears as itself, but a control character turns into a string starting with ‘C-’, a meta character turns into a string starting with ‘M-’, and space, tab, etc. appear as ‘SPC’, ‘TAB’, etc. A function key symbol appears inside angle brackets ‘<...>’. An event that is a list appears as the name of the symbol in the car of the list, inside angle brackets.
If the optional argument no-angles is non-
nil, the angle brackets around function keys and event symbols are omitted; this is for compatibility with old versions of Emacs which didn't use the brackets.(single-key-description ?\C-x) => "C-x" (key-description "\C-x \M-y \n \t \r \f123") => "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3" (single-key-description 'delete) => "<delete>" (single-key-description 'C-mouse-1) => "<C-mouse-1>" (single-key-description 'C-mouse-1 t) => "C-mouse-1"
This function returns a string describing character in the standard Emacs notation for characters that appear in text—like
single-key-description, except that control characters are represented with a leading caret (which is how control characters in Emacs buffers are usually displayed).(text-char-description ?\C-c) => "^C" (text-char-description ?\M-m) => "M-m" (text-char-description ?\C-\M-m) => "M-^M"
This function is used mainly for operating on keyboard macros, but it can also be used as a rough inverse for
key-description. You call it with a string containing key descriptions, separated by spaces; it returns a string or vector containing the corresponding events. (This may or may not be a single valid key sequence, depending on what events you use; see Keymap Terminology.)
Emacs provides a variety of on-line help functions, all accessible to the user as subcommands of the prefix C-h. For more information about them, see Help. Here we describe some program-level interfaces to the same information.
This function finds all symbols whose names contain a match for the regular expression regexp, and returns a list of them (see Regular Expressions). It also displays the symbols in a buffer named ‘*Help*’, each with a one-line description taken from the beginning of its documentation string.
If do-all is non-
nil, thenaproposalso shows key bindings for the functions that are found; it also shows all symbols, even those that are neither functions nor variables.In the first of the following examples,
aproposfinds all the symbols with names containing ‘exec’. (We don't show here the output that results in the ‘*Help*’ buffer.)(apropos "exec") => (Buffer-menu-execute command-execute exec-directory exec-path execute-extended-command execute-kbd-macro executing-kbd-macro executing-macro)
The value of this variable is a local keymap for characters following the Help key, C-h.
This symbol is not a function; its function definition cell holds the keymap known as
help-map. It is defined in help.el as follows:(define-key global-map "\C-h" 'help-command) (fset 'help-command help-map)
This function builds a string that explains how to restore the previous state of the windows after a help command. After building the message, it applies function to it if function is non-
nil. Otherwise it callsmessageto display it in the echo area.This function expects to be called inside a
with-output-to-temp-bufferspecial form, and expectsstandard-outputto have the value bound by that special form. For an example of its use, see the long example in Accessing Documentation.
The value of this variable is the help character—the character that Emacs recognizes as meaning Help. By default, its value is 8, which stands for C-h. When Emacs reads this character, if
help-formis a non-nilLisp expression, it evaluates that expression, and displays the result in a window if it is a string.Usually the value of
help-formisnil. Then the help character has no special meaning at the level of command input, and it becomes part of a key sequence in the normal way. The standard key binding of C-h is a prefix key for several general-purpose help features.The help character is special after prefix keys, too. If it has no binding as a subcommand of the prefix key, it runs
describe-prefix-bindings, which displays a list of all the subcommands of the prefix key.
The value of this variable is a list of event types that serve as alternative “help characters.” These events are handled just like the event specified by
help-char.
If this variable is non-
nil, its value is a form to evaluate whenever the characterhelp-charis read. If evaluating the form produces a string, that string is displayed.A command that calls
read-eventorread-charprobably should bindhelp-formto a non-nilexpression while it does input. (The time when you should not do this is when C-h has some other meaning.) Evaluating this expression should result in a string that explains what the input is for and how to enter it properly.Entry to the minibuffer binds this variable to the value of
minibuffer-help-form(see Minibuffer Misc).
This variable holds a function to print help for a prefix key. The function is called when the user types a prefix key followed by the help character, and the help character has no binding after that prefix. The variable's default value is
describe-prefix-bindings.
This function calls
describe-bindingsto display a list of all the subcommands of the prefix key of the most recent key sequence. The prefix described consists of all but the last event of that key sequence. (The last event is, presumably, the help character.)
The following two functions are meant for modes that want to provide help without relinquishing control, such as the “electric” modes. Their names begin with ‘Helper’ to distinguish them from the ordinary help functions.
This command pops up a window displaying a help buffer containing a listing of all of the key bindings from both the local and global keymaps. It works by calling
describe-bindings.
This command provides help for the current mode. It prompts the user in the minibuffer with the message ‘Help (Type ? for further options)’, and then provides assistance in finding out what the key bindings are, and what the mode is intended for. It returns
nil.This can be customized by changing the map
Helper-help-map.
This variable holds the name of the directory in which Emacs finds certain documentation and text files that come with Emacs. In older Emacs versions,
exec-directorywas used for this.
This macro defines a help command named fname that acts like a prefix key that shows a list of the subcommands it offers.
When invoked, fname displays help-text in a window, then reads and executes a key sequence according to help-map. The string help-text should describe the bindings available in help-map.
The command fname is defined to handle a few events itself, by scrolling the display of help-text. When fname reads one of those special events, it does the scrolling and then reads another event. When it reads an event that is not one of those few, and which has a binding in help-map, it executes that key's binding and then returns.
The argument help-line should be a single-line summary of the alternatives in help-map. In the current version of Emacs, this argument is used only if you set the option
three-step-helptot.This macro is used in the command
help-for-helpwhich is the binding of C-h C-h.
If this variable is non-
nil, commands defined withmake-help-screendisplay their help-line strings in the echo area at first, and display the longer help-text strings only if the user types the help character again.
In Emacs, you can find, create, view, save, and otherwise work with files and file directories. This chapter describes most of the file-related functions of Emacs Lisp, but a few others are described in Buffers, and those related to backups and auto-saving are described in Backups and Auto-Saving.
Many of the file functions take one or more arguments that are file
names. A file name is actually a string. Most of these functions
expand file name arguments by calling expand-file-name, so that
~ is handled correctly, as are relative file names (including
‘../’). These functions don't recognize environment variable
substitutions such as ‘$HOME’. See File Name Expansion.
When file I/O functions signal Lisp errors, they usually use the
condition file-error (see Handling Errors). The error
message is in most cases obtained from the operating system, according
to locale system-message-locale, and decoded using coding system
locale-coding-system (see Locales).
Visiting a file means reading a file into a buffer. Once this is done, we say that the buffer is visiting that file, and call the file “the visited file” of the buffer.
A file and a buffer are two different things. A file is information recorded permanently in the computer (unless you delete it). A buffer, on the other hand, is information inside of Emacs that will vanish at the end of the editing session (or when you kill the buffer). Usually, a buffer contains information that you have copied from a file; then we say the buffer is visiting that file. The copy in the buffer is what you modify with editing commands. Such changes to the buffer do not change the file; therefore, to make the changes permanent, you must save the buffer, which means copying the altered buffer contents back into the file.
In spite of the distinction between files and buffers, people often refer to a file when they mean a buffer and vice-versa. Indeed, we say, “I am editing a file,” rather than, “I am editing a buffer that I will soon save as a file of the same name.” Humans do not usually need to make the distinction explicit. When dealing with a computer program, however, it is good to keep the distinction in mind.
This section describes the functions normally used to visit files. For historical reasons, these functions have names starting with ‘find-’ rather than ‘visit-’. See Buffer File Name, for functions and variables that access the visited file name of a buffer or that find an existing buffer by its visited file name.
In a Lisp program, if you want to look at the contents of a file but
not alter it, the fastest way is to use insert-file-contents in a
temporary buffer. Visiting the file is not necessary and takes longer.
See Reading from Files.
This command selects a buffer visiting the file filename, using an existing buffer if there is one, and otherwise creating a new buffer and reading the file into it. It also returns that buffer.
The body of the
find-filefunction is very simple and looks like this:(switch-to-buffer (find-file-noselect filename))(See
switch-to-bufferin Displaying Buffers.)If wildcards is non-
nil, which is always true in an interactive call, thenfind-fileexpands wildcard characters in filename and visits all the matching files.When
find-fileis called interactively, it prompts for filename in the minibuffer.
This function is the guts of all the file-visiting functions. It finds or creates a buffer visiting the file filename, and returns it. It uses an existing buffer if there is one, and otherwise creates a new buffer and reads the file into it. You may make the buffer current or display it in a window if you wish, but this function does not do so.
If wildcards is non-
nil, thenfind-file-noselectexpands wildcard characters in filename and visits all the matching files.When
find-file-noselectuses an existing buffer, it first verifies that the file has not changed since it was last visited or saved in that buffer. If the file has changed, then this function asks the user whether to reread the changed file. If the user says ‘yes’, any changes previously made in the buffer are lost.This function displays warning or advisory messages in various peculiar cases, unless the optional argument nowarn is non-
nil. For example, if it needs to create a buffer, and there is no file named filename, it displays the message ‘(New file)’ in the echo area, and leaves the buffer empty.The
find-file-noselectfunction normally callsafter-find-fileafter reading the file (see Subroutines of Visiting). That function sets the buffer major mode, parses local variables, warns the user if there exists an auto-save file more recent than the file just visited, and finishes by running the functions infind-file-hooks.If the optional argument rawfile is non-
nil, thenafter-find-fileis not called, and thefind-file-not-found-hooksare not run in case of failure. What's more, a non-nilrawfile value suppresses coding system conversion (see Coding Systems) and format conversion (see Format Conversion).The
find-file-noselectfunction usually returns the buffer that is visiting the file filename. But, if wildcards are actually used and expanded, it returns a list of buffers that are visiting the various files.(find-file-noselect "/etc/fstab") => #<buffer fstab>
This command selects a buffer visiting the file filename, but does so in a window other than the selected window. It may use another existing window or split a window; see Displaying Buffers.
When this command is called interactively, it prompts for filename.
This command selects a buffer visiting the file filename, like
find-file, but it marks the buffer as read-only. See Read Only Buffers, for related functions and variables.When this command is called interactively, it prompts for filename.
This command visits filename using View mode, returning to the previous buffer when you exit View mode. View mode is a minor mode that provides commands to skim rapidly through the file, but does not let you modify the text. Entering View mode runs the normal hook
view-mode-hook. See Hooks.When
view-fileis called interactively, it prompts for filename.
If this variable is non-
nil, then the variousfind-filecommands check for wildcard characters and visit all the files that match them. If this isnil, then wildcard characters are not treated specially.
The value of this variable is a list of functions to be called after a file is visited. The file's local-variables specification (if any) will have been processed before the hooks are run. The buffer visiting the file is current when the hook functions are run.
This variable works just like a normal hook, but we think that renaming it would not be advisable. See Hooks.
The value of this variable is a list of functions to be called when
find-fileorfind-file-noselectis passed a nonexistent file name.find-file-noselectcalls these functions as soon as it detects a nonexistent file. It calls them in the order of the list, until one of them returns non-nil.buffer-file-nameis already set up.This is not a normal hook because the values of the functions are used, and in many cases only some of the functions are called.
The find-file-noselect function uses two important subroutines
which are sometimes useful in user Lisp code: create-file-buffer
and after-find-file. This section explains how to use them.
This function creates a suitably named buffer for visiting filename, and returns it. It uses filename (sans directory) as the name if that name is free; otherwise, it appends a string such as ‘<2>’ to get an unused name. See also Creating Buffers.
Please note:
create-file-bufferdoes not associate the new buffer with a file and does not select the buffer. It also does not use the default major mode.(create-file-buffer "foo") => #<buffer foo> (create-file-buffer "foo") => #<buffer foo<2>> (create-file-buffer "foo") => #<buffer foo<3>>This function is used by
find-file-noselect. It usesgenerate-new-buffer(see Creating Buffers).
This function sets the buffer major mode, and parses local variables (see Auto Major Mode). It is called by
find-file-noselectand by the default revert function (see Reverting).If reading the file got an error because the file does not exist, but its directory does exist, the caller should pass a non-
nilvalue for error. In that case,after-find-fileissues a warning: ‘(New file)’. For more serious errors, the caller should usually not callafter-find-file.If warn is non-
nil, then this function issues a warning if an auto-save file exists and is more recent than the visited file.If noauto is non-
nil, that says not to enable or disable Auto-Save mode. The mode remains enabled if it was enabled before.If after-find-file-from-revert-buffer is non-
nil, that means this call was fromrevert-buffer. This has no direct effect, but some mode functions and hook functions check the value of this variable.If nomodes is non-
nil, that means don't alter the buffer's major mode, don't process local variables specifications in the file, and don't runfind-file-hooks. This feature is used byrevert-bufferin some cases.The last thing
after-find-filedoes is call all the functions in the listfind-file-hooks.
When you edit a file in Emacs, you are actually working on a buffer that is visiting that file—that is, the contents of the file are copied into the buffer and the copy is what you edit. Changes to the buffer do not change the file until you save the buffer, which means copying the contents of the buffer into the file.
This function saves the contents of the current buffer in its visited file if the buffer has been modified since it was last visited or saved. Otherwise it does nothing.
save-bufferis responsible for making backup files. Normally, backup-option isnil, andsave-buffermakes a backup file only if this is the first save since visiting the file. Other values for backup-option request the making of backup files in other circumstances:
- With an argument of 4 or 64, reflecting 1 or 3 C-u's, the
save-bufferfunction marks this version of the file to be backed up when the buffer is next saved.- With an argument of 16 or 64, reflecting 2 or 3 C-u's, the
save-bufferfunction unconditionally backs up the previous version of the file before saving it.
This command saves some modified file-visiting buffers. Normally it asks the user about each buffer. But if save-silently-p is non-
nil, it saves all the file-visiting buffers without querying the user.The optional pred argument controls which buffers to ask about. If it is
nil, that means to ask only about file-visiting buffers. If it ist, that means also offer to save certain other non-file buffers—those that have a non-nilbuffer-local value ofbuffer-offer-save. (A user who says ‘yes’ to saving a non-file buffer is asked to specify the file name to use.) Thesave-buffers-kill-emacsfunction passes the valuetfor pred.If pred is neither
tnornil, then it should be a function of no arguments. It will be called in each buffer to decide whether to offer to save that buffer. If it returns a non-nilvalue in a certain buffer, that means do offer to save that buffer.
This function writes the current buffer into file filename, makes the buffer visit that file, and marks it not modified. Then it renames the buffer based on filename, appending a string like ‘<2>’ if necessary to make a unique buffer name. It does most of this work by calling
set-visited-file-name(see Buffer File Name) andsave-buffer.If confirm is non-
nil, that means to ask for confirmation before overwriting an existing file.
Saving a buffer runs several hooks. It also performs format conversion (see Format Conversion), and may save text properties in “annotations” (see Saving Properties).
The value of this variable is a list of functions to be called before writing out a buffer to its visited file. If one of them returns non-
nil, the file is considered already written and the rest of the functions are not called, nor is the usual code for writing the file executed.If a function in
write-file-hooksreturns non-nil, it is responsible for making a backup file (if that is appropriate). To do so, execute the following code:(or buffer-backed-up (backup-buffer))You might wish to save the file modes value returned by
backup-bufferand use that to set the mode bits of the file that you write. This is whatsave-buffernormally does.The hook functions in
write-file-hooksare also responsible for encoding the data (if desired): they must choose a suitable coding system (see Lisp and Coding Systems), perform the encoding (see Explicit Encoding), and setlast-coding-system-usedto the coding system that was used (see Encoding and I/O).Do not make this variable buffer-local. To set up buffer-specific hook functions, use
write-contents-hooksinstead.Even though this is not a normal hook, you can use
add-hookandremove-hookto manipulate the list. See Hooks.
This works just like
write-file-hooks, but it is intended to be made buffer-local in particular buffers, and used for hooks that pertain to the file name or the way the buffer contents were obtained.The variable is marked as a permanent local, so that changing the major mode does not alter a buffer-local value. This is convenient for packages that read “file” contents in special ways, and set up hooks to save the data in a corresponding way.
This works just like
write-file-hooks, but it is intended for hooks that pertain to the contents of the file, as opposed to hooks that pertain to where the file came from. Such hooks are usually set up by major modes, as buffer-local bindings for this variable.This variable automatically becomes buffer-local whenever it is set; switching to a new major mode always resets this variable. When you use
add-hooksto add an element to this hook, you should not specify a non-nillocal argument, since this variable is used only buffer-locally.
This normal hook runs after a buffer has been saved in its visited file. One use of this hook is in Fast Lock mode; it uses this hook to save the highlighting information in a cache file.
If this variable is non-
nil, thensave-bufferprotects against I/O errors while saving by writing the new file to a temporary name instead of the name it is supposed to have, and then renaming it to the intended name after it is clear there are no errors. This procedure prevents problems such as a lack of disk space from resulting in an invalid file.As a side effect, backups are necessarily made by copying. See Rename or Copy. Yet, at the same time, saving a precious file always breaks all hard links between the file you save and other file names.
Some modes give this variable a non-
nilbuffer-local value in particular buffers.
This variable determines whether files may be written out that do not end with a newline. If the value of the variable is
t, thensave-buffersilently adds a newline at the end of the file whenever the buffer being saved does not already end in one. If the value of the variable is non-nil, but nott, thensave-bufferasks the user whether to add a newline each time the case arises.If the value of the variable is
nil, thensave-bufferdoesn't add newlines at all.nilis the default value, but a few major modes set it totin particular buffers.
See also the function set-visited-file-name (see Buffer File Name).
You can copy a file from the disk and insert it into a buffer
using the insert-file-contents function. Don't use the user-level
command insert-file in a Lisp program, as that sets the mark.
This function inserts the contents of file filename into the current buffer after point. It returns a list of the absolute file name and the length of the data inserted. An error is signaled if filename is not the name of a file that can be read.
The function
insert-file-contentschecks the file contents against the defined file formats, and converts the file contents if appropriate. See Format Conversion. It also calls the functions in the listafter-insert-file-functions; see Saving Properties. Normally, one of the functions in theafter-insert-file-functionslist determines the coding system (see Coding Systems) used for decoding the file's contents.If visit is non-
nil, this function additionally marks the buffer as unmodified and sets up various fields in the buffer so that it is visiting the file filename: these include the buffer's visited file name and its last save file modtime. This feature is used byfind-file-noselectand you probably should not use it yourself.If beg and end are non-
nil, they should be integers specifying the portion of the file to insert. In this case, visit must benil. For example,(insert-file-contents filename nil 0 500)inserts the first 500 characters of a file.
If the argument replace is non-
nil, it means to replace the contents of the buffer (actually, just the accessible portion) with the contents of the file. This is better than simply deleting the buffer contents and inserting the whole file, because (1) it preserves some marker positions and (2) it puts less data in the undo list.It is possible to read a special file (such as a FIFO or an I/O device) with
insert-file-contents, as long as replace and visit arenil.
This function works like
insert-file-contentsexcept that it does not do format decoding (see Format Conversion), does not do character code conversion (see Coding Systems), does not runfind-file-hooks, does not perform automatic uncompression, and so on.
If you want to pass a file name to another process so that another
program can read the file, use the function file-local-copy; see
Magic File Names.
You can write the contents of a buffer, or part of a buffer, directly
to a file on disk using the append-to-file and
write-region functions. Don't use these functions to write to
files that are being visited; that could cause confusion in the
mechanisms for visiting.
This function appends the contents of the region delimited by start and end in the current buffer to the end of file filename. If that file does not exist, it is created. This function returns
nil.An error is signaled if filename specifies a nonwritable file, or a nonexistent file in a directory where files cannot be created.
This function writes the region delimited by start and end in the current buffer into the file specified by filename.
If start is a string, then
write-regionwrites or appends that string, rather than text from the buffer. end is ignored in this case.If append is non-
nil, then the specified text is appended to the existing file contents (if any). Starting in Emacs 21, if append is an integer, thenwrite-regionseeks to that byte offset from the start of the file and writes the data from there.If mustbenew is non-
nil, thenwrite-regionasks for confirmation if filename names an existing file. Starting in Emacs 21, if mustbenew is the symbolexcl, thenwrite-regiondoes not ask for confirmation, but instead it signals an errorfile-already-existsif the file already exists.The test for an existing file, when mustbenew is
excl, uses a special system feature. At least for files on a local disk, there is no chance that some other program could create a file of the same name before Emacs does, without Emacs's noticing.If visit is
t, then Emacs establishes an association between the buffer and the file: the buffer is then visiting that file. It also sets the last file modification time for the current buffer to filename's modtime, and marks the buffer as not modified. This feature is used bysave-buffer, but you probably should not use it yourself.If visit is a string, it specifies the file name to visit. This way, you can write the data to one file (filename) while recording the buffer as visiting another file (visit). The argument visit is used in the echo area message and also for file locking; visit is stored in
buffer-file-name. This feature is used to implementfile-precious-flag; don't use it yourself unless you really know what you're doing.The optional argument lockname, if non-
nil, specifies the file name to use for purposes of locking and unlocking, overriding filename and visit for that purpose.The function
write-regionconverts the data which it writes to the appropriate file formats specified bybuffer-file-format. See Format Conversion. It also calls the functions in the listwrite-region-annotate-functions; see Saving Properties.Normally,
write-regiondisplays the message ‘Wrote filename’ in the echo area. If visit is neithertnornilnor a string, then this message is inhibited. This feature is useful for programs that use files for internal purposes, files that the user does not need to know about.
The
with-temp-filemacro evaluates the body forms with a temporary buffer as the current buffer; then, at the end, it writes the buffer contents into file file. It kills the temporary buffer when finished, restoring the buffer that was current before thewith-temp-fileform. Then it returns the value of the last form in body.The current buffer is restored even in case of an abnormal exit via
throwor error (see Nonlocal Exits).See also
with-temp-bufferin Current Buffer.
When two users edit the same file at the same time, they are likely to interfere with each other. Emacs tries to prevent this situation from arising by recording a file lock when a file is being modified. Emacs can then detect the first attempt to modify a buffer visiting a file that is locked by another Emacs job, and ask the user what to do. The file lock is really a file, a symbolic link with a special name, stored in the same directory as the file you are editing.
When you access files using NFS, there may be a small probability that you and another user will both lock the same file “simultaneously”. If this happens, it is possible for the two users to make changes simultaneously, but Emacs will still warn the user who saves second. Also, the detection of modification of a buffer visiting a file changed on disk catches some cases of simultaneous editing; see Modification Time.
This function returns
nilif the file filename is not locked. It returnstif it is locked by this Emacs process, and it returns the name of the user who has locked it if it is locked by some other job.(file-locked-p "foo") => nil
This function locks the file filename, if the current buffer is modified. The argument filename defaults to the current buffer's visited file. Nothing is done if the current buffer is not visiting a file, or is not modified.
This function unlocks the file being visited in the current buffer, if the buffer is modified. If the buffer is not modified, then the file should not be locked, so this function does nothing. It also does nothing if the current buffer is not visiting a file.
File locking is not supported on some systems. On systems that do not
support it, the functions lock-buffer, unlock-buffer and
file-locked-p do nothing and return nil.
This function is called when the user tries to modify file, but it is locked by another user named other-user. The default definition of this function asks the user to say what to do. The value this function returns determines what Emacs does next:
- A value of
tsays to grab the lock on the file. Then this user may edit the file and other-user loses the lock.- A value of
nilsays to ignore the lock and let this user edit the file anyway.- This function may instead signal a
file-lockederror, in which case the change that the user was about to make does not take place.The error message for this error looks like this:
error--> File is locked: file other-userwhere
fileis the name of the file and other-user is the name of the user who has locked the file.If you wish, you can replace the
ask-user-about-lockfunction with your own version that makes the decision in another way. The code for its usual definition is in userlock.el.
The functions described in this section all operate on strings that designate file names. All the functions have names that begin with the word ‘file’. These functions all return information about actual files or directories, so their arguments must all exist as actual files or directories unless otherwise noted.
These functions test for permission to access a file in specific ways.
This function returns
tif a file named filename appears to exist. This does not mean you can necessarily read the file, only that you can find out its attributes. (On Unix and GNU/Linux, this is true if the file exists and you have execute permission on the containing directories, regardless of the protection of the file itself.)If the file does not exist, or if fascist access control policies prevent you from finding the attributes of the file, this function returns
nil.
This function returns
tif a file named filename exists and you can read it. It returnsnilotherwise.(file-readable-p "files.texi") => t (file-exists-p "/usr/spool/mqueue") => t (file-readable-p "/usr/spool/mqueue") => nil
This function returns
tif a file named filename exists and you can execute it. It returnsnilotherwise. On Unix and GNU/Linux, if the file is a directory, execute permission means you can check the existence and attributes of files inside the directory, and open those files if their modes permit.
This function returns
tif the file filename can be written or created by you, andnilotherwise. A file is writable if the file exists and you can write it. It is creatable if it does not exist, but the specified directory does exist and you can write in that directory.In the third example below, foo is not writable because the parent directory does not exist, even though the user could create such a directory.
(file-writable-p "~/foo") => t (file-writable-p "/foo") => nil (file-writable-p "~/no-such-dir/foo") => nil
This function returns
tif you have permission to open existing files in the directory whose name as a file is dirname; otherwise (or if there is no such directory), it returnsnil. The value of dirname may be either a directory name or the file name of a file which is a directory.Example: after the following,
(file-accessible-directory-p "/foo") => nilwe can deduce that any attempt to read a file in /foo/ will give an error.
This function opens file filename for reading, then closes it and returns
nil. However, if the open fails, it signals an error using string as the error message text.
This function returns
tif deleting the file filename and then creating it anew would keep the file's owner unchanged.
This function returns
tif the file filename1 is newer than file filename2. If filename1 does not exist, it returnsnil. If filename2 does not exist, it returnst.In the following example, assume that the file aug-19 was written on the 19th, aug-20 was written on the 20th, and the file no-file doesn't exist at all.
(file-newer-than-file-p "aug-19" "aug-20") => nil (file-newer-than-file-p "aug-20" "aug-19") => t (file-newer-than-file-p "aug-19" "no-file") => t (file-newer-than-file-p "no-file" "aug-19") => nilYou can use
file-attributesto get a file's last modification time as a list of two numbers. See File Attributes.
This section describes how to distinguish various kinds of files, such as directories, symbolic links, and ordinary files.
If the file filename is a symbolic link, the
file-symlink-pfunction returns the file name to which it is linked. This may be the name of a text file, a directory, or even another symbolic link, or it may be a nonexistent file name.If the file filename is not a symbolic link (or there is no such file),
file-symlink-preturnsnil.(file-symlink-p "foo") => nil (file-symlink-p "sym-link") => "foo" (file-symlink-p "sym-link2") => "sym-link" (file-symlink-p "/bin") => "/pub/bin"
This function returns
tif filename is the name of an existing directory,nilotherwise.(file-directory-p "~rms") => t (file-directory-p "~rms/lewis/files.texi") => nil (file-directory-p "~rms/lewis/no-such-file") => nil (file-directory-p "$HOME") => nil (file-directory-p (substitute-in-file-name "$HOME")) => t
This function returns
tif the file filename exists and is a regular file (not a directory, named pipe, terminal, or other I/O device).
The truename of a file is the name that you get by following symbolic links at all levels until none remain, then simplifying away ‘.’ and ‘..’ appearing as name components. This results in a sort of canonical name for the file. A file does not always have a unique truename; the number of distinct truenames a file has is equal to the number of hard links to the file. However, truenames are useful because they eliminate symbolic links as a cause of name variation.
The function
file-truenamereturns the truename of the file filename. The argument must be an absolute file name.
This function follows symbolic links, starting with filename, until it finds a file name which is not the name of a symbolic link. Then it returns that file name.
To illustrate the difference between file-chase-links and
file-truename, suppose that /usr/foo is a symbolic link to
the directory /home/foo, and /home/foo/hello is an
ordinary file (or at least, not a symbolic link) or nonexistent. Then
we would have:
(file-chase-links "/usr/foo/hello")
;; This does not follow the links in the parent directories.
=> "/usr/foo/hello"
(file-truename "/usr/foo/hello")
;; Assuming that /home is not a symbolic link.
=> "/home/foo/hello"
See Buffer File Name, for related information.
This section describes the functions for getting detailed information about a file, other than its contents. This information includes the mode bits that control access permission, the owner and group numbers, the number of names, the inode number, the size, and the times of access and modification.
This function returns the mode bits of filename, as an integer. The mode bits are also called the file permissions, and they specify access control in the usual Unix fashion. If the low-order bit is 1, then the file is executable by all users, if the second-lowest-order bit is 1, then the file is writable by all users, etc.
The highest value returnable is 4095 (7777 octal), meaning that everyone has read, write, and execute permission, that the suid bit is set for both others and group, and that the sticky bit is set.
(file-modes "~/junk/diffs") => 492 ; Decimal integer. (format "%o" 492) => "754" ; Convert to octal. (set-file-modes "~/junk/diffs" 438) => nil (format "%o" 438) => "666" ; Convert to octal. % ls -l diffs -rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs
This functions returns the number of names (i.e., hard links) that file filename has. If the file does not exist, then this function returns
nil. Note that symbolic links have no effect on this function, because they are not considered to be names of the files they link to.% ls -l foo* -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1 (file-nlinks "foo") => 2 (file-nlinks "doesnt-exist") => nil
This function returns a list of attributes of file filename. If the specified file cannot be opened, it returns
nil.The elements of the list, in order, are:
tfor a directory, a string for a symbolic link (the name linked to), ornilfor a text file.- The number of names the file has. Alternate names, also known as hard links, can be created by using the
add-name-to-filefunction (see Changing Files).- The file's uid.
- The file's gid.
- The time of last access, as a list of two integers. The first integer has the high-order 16 bits of time, the second has the low 16 bits. (This is similar to the value of
current-time; see Time of Day.)- The time of last modification as a list of two integers (as above).
- The time of last status change as a list of two integers (as above).
- The size of the file in bytes. If the size is too large to fit in a Lisp integer, this is a floating point number.
- The file's modes, as a string of ten letters or dashes, as in ‘ls -l’.
tif the file's gid would change if file were deleted and recreated;nilotherwise.- The file's inode number. If possible, this is an integer. If the inode number is too large to be represented as an integer in Emacs Lisp, then the value has the form
(high.low), where low holds the low 16 bits.- The file system number of the file system that the file is in. Depending on the magnitude of the value, this can be either an integer or a cons cell, in the same manner as the inode number. This element and the file's inode number together give enough information to distinguish any two files on the system—no two files can have the same values for both of these numbers.
For example, here are the file attributes for files.texi:
(file-attributes "files.texi") => (nil 1 2235 75 (8489 20284) (8489 20284) (8489 20285) 14906 "-rw-rw-rw-" nil 129500 -32252)and here is how the result is interpreted:
nil- is neither a directory nor a symbolic link.
1- has only one name (the name files.texi in the current default directory).
2235- is owned by the user with uid 2235.
75- is in the group with gid 75.
(8489 20284)- was last accessed on Aug 19 00:09.
(8489 20284)- was last modified on Aug 19 00:09.
(8489 20285)- last had its inode changed on Aug 19 00:09.
14906- is 14906 bytes long. (It may not contain 14906 characters, though, if some of the bytes belong to multibyte sequences.)
"-rw-rw-rw-"- has a mode of read and write access for the owner, group, and world.
nil- would retain the same gid if it were recreated.
129500- has an inode number of 129500.
-32252- is on file system number -32252.
The functions in this section rename, copy, delete, link, and set the modes of files.
In the functions that have an argument newname, if a file by the name of newname already exists, the actions taken depend on the value of the argument ok-if-already-exists:
file-already-exists error if
ok-if-already-exists is nil.
This function gives the file named oldname the additional name newname. This means that newname becomes a new “hard link” to oldname.
In the first part of the following example, we list two files, foo and foo3.
% ls -li fo* 81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3Now we create a hard link, by calling
add-name-to-file, then list the files again. This shows two names for one file, foo and foo2.(add-name-to-file "foo" "foo2") => nil % ls -li fo* 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3Finally, we evaluate the following:
(add-name-to-file "foo" "foo3" t)and list the files again. Now there are three names for one file: foo, foo2, and foo3. The old contents of foo3 are lost.
(add-name-to-file "foo1" "foo3") => nil % ls -li fo* 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3This function is meaningless on operating systems where multiple names for one file are not allowed. Some systems implement multiple names by copying the file instead.
See also
file-nlinksin File Attributes.
This command renames the file filename as newname.
If filename has additional names aside from filename, it continues to have those names. In fact, adding the name newname with
add-name-to-fileand then deleting filename has the same effect as renaming, aside from momentary intermediate states.In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
This command copies the file oldname to newname. An error is signaled if oldname does not exist.
If time is non-
nil, then this function gives the new file the same last-modified time that the old one has. (This works on only some operating systems.) If setting the time gets an error,copy-filesignals afile-date-errorerror.In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
This command deletes the file filename, like the shell command ‘rm filename’. If the file has multiple names, it continues to exist under the other names.
A suitable kind of
file-errorerror is signaled if the file does not exist, or is not deletable. (On Unix and GNU/Linux, a file is deletable if its directory is writable.)See also
delete-directoryin Create/Delete Dirs.
This command makes a symbolic link to filename, named newname. This is like the shell command ‘ln -s filename newname’.
In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
This function is not available on systems that don't support symbolic links.
This function defines the logical name name to have the value string. It is available only on VMS.
This function sets mode bits of filename to mode (which must be an integer). Only the low 12 bits of mode are used.
This function sets the default file protection for new files created by Emacs and its subprocesses. Every file created with Emacs initially has this protection, or a subset of it (
write-regionwill not give a file execute permission even if the default file protection allows execute permission). On Unix and GNU/Linux, the default protection is the bitwise complement of the “umask” value.The argument mode must be an integer. On most systems, only the low 9 bits of mode are meaningful. You can use the Lisp construct for octal character codes to enter mode; for example,
(set-default-file-modes ?\644)Saving a modified version of an existing file does not count as creating the file; it preserves the existing file's mode, whatever that is. So the default file protection has no effect.
On MS-DOS, there is no such thing as an “executable” file mode bit.
So Emacs considers a file executable if its name ends in one of the
standard executable extensions, such as .com, .bat,
.exe, and some others. Files that begin with the Unix-standard
‘#!’ signature, such as shell and Perl scripts, are also considered
as executable files. This is reflected in the values returned by
file-modes and file-attributes. Directories are also
reported with executable bit set, for compatibility with Unix.
Files are generally referred to by their names, in Emacs as elsewhere. File names in Emacs are represented as strings. The functions that operate on a file all expect a file name argument.
In addition to operating on files themselves, Emacs Lisp programs often need to operate on file names; i.e., to take them apart and to use part of a name to construct related file names. This section describes how to manipulate file names.
The functions in this section do not actually access files, so they can operate on file names that do not refer to an existing file or directory.
On MS-DOS and MS-Windows, these functions (like the function that actually operate on files) accept MS-DOS or MS-Windows file-name syntax, where backslashes separate the components, as well as Unix syntax; but they always return Unix syntax. On VMS, these functions (and the ones that operate on files) understand both VMS file-name syntax and Unix syntax. This enables Lisp programs to specify file names in Unix syntax and work properly on all systems without change.
The operating system groups files into directories. To specify a file, you must specify the directory and the file's name within that directory. Therefore, Emacs considers a file name as having two main parts: the directory name part, and the nondirectory part (or file name within the directory). Either part may be empty. Concatenating these two parts reproduces the original file name.
On most systems, the directory part is everything up to and including the last slash (backslash is also allowed in input on MS-DOS or MS-Windows); the nondirectory part is the rest. The rules in VMS syntax are complicated.
For some purposes, the nondirectory part is further subdivided into the name proper and the version number. On most systems, only backup files have version numbers in their names. On VMS, every file has a version number, but most of the time the file name actually used in Emacs omits the version number, so that version numbers in Emacs are found mostly in directory lists.
This function returns the directory part of filename (or
nilif filename does not include a directory part). On most systems, the function returns a string ending in a slash. On VMS, it returns a string ending in one of the three characters ‘:’, ‘]’, or ‘>’.(file-name-directory "lewis/foo") ; Unix example => "lewis/" (file-name-directory "foo") ; Unix example => nil (file-name-directory "[X]FOO.TMP") ; VMS example => "[X]"
This function returns the nondirectory part of filename.
(file-name-nondirectory "lewis/foo") => "foo" (file-name-nondirectory "foo") => "foo" ;; The following example is accurate only on VMS. (file-name-nondirectory "[X]FOO.TMP") => "FOO.TMP"
This function returns filename with any file version numbers, backup version numbers, or trailing tildes discarded.
If keep-backup-version is non-
nil, then true file version numbers understood as such by the file system are discarded from the return value, but backup version numbers are kept.(file-name-sans-versions "~rms/foo.~1~") => "~rms/foo" (file-name-sans-versions "~rms/foo~") => "~rms/foo" (file-name-sans-versions "~rms/foo") => "~rms/foo" ;; The following example applies to VMS only. (file-name-sans-versions "foo;23") => "foo"
This function returns filename minus its “extension,” if any. The extension, in a file name, is the part that starts with the last ‘.’ in the last name component. For example,
(file-name-sans-extension "foo.lose.c") => "foo.lose" (file-name-sans-extension "big.hack/foo") => "big.hack/foo"
This function returns filename's final “extension,” if any, after applying
file-name-sans-versionsto remove any version/backup part. If period is non-nil, then the returned value includes the period that delimits the extension, and if filename has no extension, the value is"".
A directory name is the name of a directory. A directory is a kind of file, and it has a file name, which is related to the directory name but not identical to it. (This is not quite the same as the usual Unix terminology.) These two different names for the same entity are related by a syntactic transformation. On most systems, this is simple: a directory name ends in a slash (or backslash), whereas the directory's name as a file lacks that slash. On VMS, the relationship is more complicated.
The difference between a directory name and its name as a file is subtle but crucial. When an Emacs variable or function argument is described as being a directory name, a file name of a directory is not acceptable.
The following two functions convert between directory names and file names. They do nothing special with environment variable substitutions such as ‘$HOME’, and the constructs ‘~’, and ‘..’.
This function returns a string representing filename in a form that the operating system will interpret as the name of a directory. On most systems, this means appending a slash to the string (if it does not already end in one). On VMS, the function converts a string of the form [X]Y.DIR.1 to the form [X.Y].
(file-name-as-directory "~rms/lewis") => "~rms/lewis/"
This function returns a string representing dirname in a form that the operating system will interpret as the name of a file. On most systems, this means removing the final slash (or backslash) from the string. On VMS, the function converts a string of the form [X.Y] to [X]Y.DIR.1.
(directory-file-name "~lewis/") => "~lewis"
Directory name abbreviations are useful for directories that are normally accessed through symbolic links. Sometimes the users recognize primarily the link's name as “the name” of the directory, and find it annoying to see the directory's “real” name. If you define the link name as an abbreviation for the “real” name, Emacs shows users the abbreviation instead.
The variable
directory-abbrev-alistcontains an alist of abbreviations to use for file directories. Each element has the form(from.to), and says to replace from with to when it appears in a directory name. The from string is actually a regular expression; it should always start with ‘^’. The functionabbreviate-file-nameperforms these substitutions.You can set this variable in site-init.el to describe the abbreviations appropriate for your site.
Here's an example, from a system on which file system /home/fsf and so on are normally accessed through symbolic links named /fsf and so on.
(("^/home/fsf" . "/fsf") ("^/home/gp" . "/gp") ("^/home/gd" . "/gd"))
To convert a directory name to its abbreviation, use this function:
This function applies abbreviations from
directory-abbrev-alistto its argument, and substitutes ‘~’ for the user's home directory.
All the directories in the file system form a tree starting at the root directory. A file name can specify all the directory names starting from the root of the tree; then it is called an absolute file name. Or it can specify the position of the file in the tree relative to a default directory; then it is called a relative file name. On Unix and GNU/Linux, an absolute file name starts with a slash or a tilde (‘~’), and a relative one does not. On MS-DOS and MS-Windows, an absolute file name starts with a slash or a backslash, or with a drive specification ‘x:/’, where x is the drive letter. The rules on VMS are complicated.
This function returns
tif file filename is an absolute file name,nilotherwise. On VMS, this function understands both Unix syntax and VMS syntax.(file-name-absolute-p "~rms/foo") => t (file-name-absolute-p "rms/foo") => nil (file-name-absolute-p "/user/rms/foo") => t
Expansion of a file name means converting a relative file name to an absolute one. Since this is done relative to a default directory, you must specify the default directory name as well as the file name to be expanded. Expansion also simplifies file names by eliminating redundancies such as ./ and name/../.
This function converts filename to an absolute file name. If directory is supplied, it is the default directory to start with if filename is relative. (The value of directory should itself be an absolute directory name; it may start with ‘~’.) Otherwise, the current buffer's value of
default-directoryis used. For example:(expand-file-name "foo") => "/xcssun/users/rms/lewis/foo" (expand-file-name "../foo") => "/xcssun/users/rms/foo" (expand-file-name "foo" "/usr/spool/") => "/usr/spool/foo" (expand-file-name "$HOME/foo") => "/xcssun/users/rms/lewis/$HOME/foo"Filenames containing ‘.’ or ‘..’ are simplified to their canonical form:
(expand-file-name "bar/../foo") => "/xcssun/users/rms/lewis/foo"Note that
expand-file-namedoes not expand environment variables; onlysubstitute-in-file-namedoes that.
This function does the inverse of expansion—it tries to return a relative name that is equivalent to filename when interpreted relative to directory. If directory is omitted or
nil, it defaults to the current buffer's default directory.On some operating systems, an absolute file name begins with a device name. On such systems, filename has no relative equivalent based on directory if they start with two different device names. In this case,
file-relative-namereturns filename in absolute form.(file-relative-name "/foo/bar" "/foo/") => "bar" (file-relative-name "/foo/bar" "/hack/") => "../foo/bar"
The value of this buffer-local variable is the default directory for the current buffer. It should be an absolute directory name; it may start with ‘~’. This variable is buffer-local in every buffer.
expand-file-nameuses the default directory when its second argument isnil.Aside from VMS, the value is always a string ending with a slash.
default-directory => "/user/lewis/manual/"
This function replaces environment variables references in filename with the environment variable values. Following standard Unix shell syntax, ‘$’ is the prefix to substitute an environment variable value.
The environment variable name is the series of alphanumeric characters (including underscores) that follow the ‘$’. If the character following the ‘$’ is a ‘{’, then the variable name is everything up to the matching ‘}’.
Here we assume that the environment variable
HOME, which holds the user's home directory name, has value ‘/xcssun/users/rms’.(substitute-in-file-name "$HOME/foo") => "/xcssun/users/rms/foo"After substitution, if a ‘~’ or a ‘/’ appears following a ‘/’, everything before the following ‘/’ is discarded:
(substitute-in-file-name "bar/~/foo") => "~/foo" (substitute-in-file-name "/usr/local/$HOME/foo") => "/xcssun/users/rms/foo" ;; /usr/local/ has been discarded.On VMS, ‘$’ substitution is not done, so this function does nothing on VMS except discard superfluous initial components as shown above.
Some programs need to write temporary files. Here is the usual way to construct a name for such a file, starting in Emacs 21:
(make-temp-file name-of-application)
The job of make-temp-file is to prevent two different users or
two different jobs from trying to use the exact same file name.
This function creates a temporary file and returns its name. The name starts with prefix; it also contains a number that is different in each Emacs job. If prefix is a relative file name, it is expanded against
temporary-file-directory.(make-temp-file "foo") => "/tmp/foo232J6v"When
make-temp-filereturns, the file has been created and is empty. At that point, you should write the intended contents into the file.If dir-flag is non-
nil,make-temp-filecreates an empty directory instead of an empty file.To prevent conflicts among different libraries running in the same Emacs, each Lisp program that uses
make-temp-fileshould have its own prefix. The number added to the end of prefix distinguishes between the same application running in different Emacs jobs. Additional added characters permit a large number of distinct names even in one Emacs job.
The default directory for temporary files is controlled by the
variable temporary-file-directory. This variable gives the user
a uniform way to specify the directory for all temporary files. Some
programs use small-temporary-file-directory instead, if that is
non-nil. To use it, you should expand the prefix against
the proper directory before calling make-temp-file.
In older Emacs versions where make-temp-file does not exist,
you should use make-temp-name instead:
(make-temp-name
(expand-file-name name-of-application
temporary-file-directory))
This function generates a string that can be used as a unique file name. The name starts with string, and contains a number that is different in each Emacs job. It is like
make-temp-fileexcept that it just constructs a name, and does not create a file. On MS-DOS, the string prefix can be truncated to fit into the 8+3 file-name limits.
This variable specifies the directory name for creating temporary files. Its value should be a directory name (see Directory Names), but it is good for Lisp programs to cope if the value is a directory's file name instead. Using the value as the second argument to
expand-file-nameis a good way to achieve that.The default value is determined in a reasonable way for your operating system; it is based on the
TMPDIR,TMPandTEMPenvironment variables, with a fall-back to a system-dependent name if none of these variables is defined.Even if you do not use
make-temp-nameto choose the temporary file's name, you should still use this variable to decide which directory to put the file in. However, if you expect the file to be small, you should usesmall-temporary-file-directoryfirst if that is non-nil.
This variable (new in Emacs 21) specifies the directory name for creating certain temporary files, which are likely to be small.
If you want to write a temporary file which is likely to be small, you should compute the directory like this:
(make-temp-file (expand-file-name prefix (or small-temporary-file-directory temporary-file-directory)))
This section describes low-level subroutines for completing a file name. For other completion functions, see Completion.
This function returns a list of all possible completions for a file whose name starts with partial-filename in directory directory. The order of the completions is the order of the files in the directory, which is unpredictable and conveys no useful information.
The argument partial-filename must be a file name containing no directory part and no slash (or backslash on some systems). The current buffer's default directory is prepended to directory, if directory is not absolute.
In the following example, suppose that ~rms/lewis is the current default directory, and has five files whose names begin with ‘f’: foo, file~, file.c, file.c.~1~, and file.c.~2~.
(file-name-all-completions "f" "") => ("foo" "file~" "file.c.~2~" "file.c.~1~" "file.c") (file-name-all-completions "fo" "") => ("foo")
This function completes the file name filename in directory directory. It returns the longest prefix common to all file names in directory directory that start with filename.
If only one match exists and filename matches it exactly, the function returns
t. The function returnsnilif directory directory contains no name starting with filename.In the following example, suppose that the current default directory has five files whose names begin with ‘f’: foo, file~, file.c, file.c.~1~, and file.c.~2~.
(file-name-completion "fi" "") => "file" (file-name-completion "file.c.~1" "") => "file.c.~1~" (file-name-completion "file.c.~1~" "") => t (file-name-completion "file.c.~3" "") => nil
file-name-completionusually ignores file names that end in any string in this list. It does not ignore them when all the possible completions end in one of these suffixes or when a buffer showing all possible completions is displayed.A typical value might look like this:
completion-ignored-extensions => (".o" ".elc" "~" ".dvi")
Most of the file names used in Lisp programs are entered by the user.
But occasionally a Lisp program needs to specify a standard file name
for a particular use—typically, to hold customization information
about each user. For example, abbrev definitions are stored (by
default) in the file ~/.abbrev_defs; the completion
package stores completions in the file ~/.completions. These are
two of the many standard file names used by parts of Emacs for certain
purposes.
Various operating systems have their own conventions for valid file
names and for which file names to use for user profile data. A Lisp
program which reads a file using a standard file name ought to use, on
each type of system, a file name suitable for that system. The function
convert-standard-filename makes this easy to do.
This function alters the file name filename to fit the conventions of the operating system in use, and returns the result as a new string.
The recommended way to specify a standard file name in a Lisp program
is to choose a name which fits the conventions of GNU and Unix systems,
usually with a nondirectory part that starts with a period, and pass it
to convert-standard-filename instead of using it directly. Here
is an example from the completion package:
(defvar save-completions-file-name
(convert-standard-filename "~/.completions")
"*The file name to save completions to.")
On GNU and Unix systems, and on some other systems as well,
convert-standard-filename returns its argument unchanged. On
some other systems, it alters the name to fit the system's conventions.
For example, on MS-DOS the alterations made by this function include converting a leading ‘.’ to ‘_’, converting a ‘_’ in the middle of the name to ‘.’ if there is no other ‘.’, inserting a ‘.’ after eight characters if there is none, and truncating to three characters after the ‘.’. (It makes other changes as well.) Thus, .abbrev_defs becomes _abbrev.def, and .completions becomes _complet.ion.
A directory is a kind of file that contains other files entered under various names. Directories are a feature of the file system.
Emacs can list the names of the files in a directory as a Lisp list,
or display the names in a buffer using the ls shell command. In
the latter case, it can optionally display information about each file,
depending on the options passed to the ls command.
This function returns a list of the names of the files in the directory directory. By default, the list is in alphabetical order.
If full-name is non-
nil, the function returns the files' absolute file names. Otherwise, it returns the names relative to the specified directory.If match-regexp is non-
nil, this function returns only those file names that contain a match for that regular expression—the other file names are excluded from the list.If nosort is non-
nil,directory-filesdoes not sort the list, so you get the file names in no particular order. Use this if you want the utmost possible speed and don't care what order the files are processed in. If the order of processing is visible to the user, then the user will probably be happier if you do sort the names.(directory-files "~lewis") => ("#foo#" "#foo.el#" "." ".." "dired-mods.el" "files.texi" "files.texi.~1~")An error is signaled if directory is not the name of a directory that can be read.
This function returns a list of all versions of the file named file in directory dirname.
This function expands the wildcard pattern pattern, returning a list of file names that match it.
If pattern is written as an absolute file name, the values are absolute also.
If pattern is written as a relative file name, it is interpreted relative to the current default directory. The file names returned are normally also relative to the current default directory. However, if full is non-
nil, they are absolute.
This function inserts (in the current buffer) a directory listing for directory file, formatted with
lsaccording to switches. It leaves point after the inserted text.The argument file may be either a directory name or a file specification including wildcard characters. If wildcard is non-
nil, that means treat file as a file specification with wildcards.If full-directory-p is non-
nil, that means the directory listing is expected to show the full contents of a directory. You should specifytwhen file is a directory and switches do not contain ‘-d’. (The ‘-d’ option tolssays to describe a directory itself as a file, rather than showing its contents.)On most systems, this function works by running a directory listing program whose name is in the variable
insert-directory-program. If wildcard is non-nil, it also runs the shell specified byshell-file-name, to expand the wildcards.MS-DOS and MS-Windows systems usually lack the standard Unix program
ls, so this function emulates the standard Unix programlswith Lisp code.
This variable's value is the program to run to generate a directory listing for the function
insert-directory. It is ignored on systems which generate the listing with Lisp code.
Most Emacs Lisp file-manipulation functions get errors when used on
files that are directories. For example, you cannot delete a directory
with delete-file. These special functions exist to create and
delete directories.
This function creates a directory named dirname. If parents is non-
nil, that means to create the parent directories first, if they don't already exist.
This function deletes the directory named dirname. The function
delete-filedoes not work for files that are directories; you must usedelete-directoryfor them. If the directory contains any files,delete-directorysignals an error.
You can implement special handling for certain file names. This is called making those names magic. The principal use for this feature is in implementing remote file names (see Remote Files).
To define a kind of magic file name, you must supply a regular expression to define the class of names (all those that match the regular expression), plus a handler that implements all the primitive Emacs file operations for file names that do match.
The variable file-name-handler-alist holds a list of handlers,
together with regular expressions that determine when to apply each
handler. Each element has this form:
(regexp . handler)
All the Emacs primitives for file access and file name transformation
check the given file name against file-name-handler-alist. If
the file name matches regexp, the primitives handle that file by
calling handler.
The first argument given to handler is the name of the primitive; the remaining arguments are the arguments that were passed to that primitive. (The first of these arguments is most often the file name itself.) For example, if you do this:
(file-exists-p filename)
and filename has handler handler, then handler is called like this:
(funcall handler 'file-exists-p filename)
When a function takes two or more arguments that must be file names, it checks each of those names for a handler. For example, if you do this:
(expand-file-name filename dirname)
then it checks for a handler for filename and then for a handler for dirname. In either case, the handler is called like this:
(funcall handler 'expand-file-name filename dirname)
The handler then needs to figure out whether to handle filename or dirname.
Here are the operations that a magic file name handler gets to handle:
add-name-to-file, copy-file, delete-directory,
delete-file,
diff-latest-backup-file,
directory-file-name,
directory-files,
dired-call-process,
dired-compress-file, dired-uncache,
expand-file-name,
file-accessible-directory-p,
file-attributes,
file-directory-p,
file-executable-p, file-exists-p,
file-local-copy,
file-modes, file-name-all-completions,
file-name-as-directory,
file-name-completion,
file-name-directory,
file-name-nondirectory,
file-name-sans-versions, file-newer-than-file-p,
file-ownership-preserved-p,
file-readable-p, file-regular-p, file-symlink-p,
file-truename, file-writable-p,
find-backup-file-name,
get-file-buffer,
insert-directory,
insert-file-contents,
load, make-directory,
make-symbolic-link, rename-file, set-file-modes,
set-visited-file-modtime, shell-command,
unhandled-file-name-directory,
vc-registered,
verify-visited-file-modtime,
write-region.
Handlers for insert-file-contents typically need to clear the
buffer's modified flag, with (set-buffer-modified-p nil), if the
visit argument is non-nil. This also has the effect of
unlocking the buffer if it is locked.
The handler function must handle all of the above operations, and possibly others to be added in the future. It need not implement all these operations itself—when it has nothing special to do for a certain operation, it can reinvoke the primitive, to handle the operation “in the usual way”. It should always reinvoke the primitive for an operation it does not recognize. Here's one way to do this:
(defun my-file-handler (operation &rest args)
;; First check for the specific operations
;; that we have special handling for.
(cond ((eq operation 'insert-file-contents) ...)
((eq operation 'write-region) ...)
...
;; Handle any operation we don't know about.
(t (let ((inhibit-file-name-handlers
(cons 'my-file-handler
(and (eq inhibit-file-name-operation operation)
inhibit-file-name-handlers)))
(inhibit-file-name-operation operation))
(apply operation args)))))
When a handler function decides to call the ordinary Emacs primitive for
the operation at hand, it needs to prevent the primitive from calling
the same handler once again, thus leading to an infinite recursion. The
example above shows how to do this, with the variables
inhibit-file-name-handlers and
inhibit-file-name-operation. Be careful to use them exactly as
shown above; the details are crucial for proper behavior in the case of
multiple handlers, and for operations that have two file names that may
each have handlers.
This variable holds a list of handlers whose use is presently inhibited for a certain operation.
The operation for which certain handlers are presently inhibited.
This function returns the handler function for file name file, or
nilif there is none. The argument operation should be the operation to be performed on the file—the value you will pass to the handler as its first argument when you call it. The operation is needed for comparison withinhibit-file-name-operation.
This function copies file filename to an ordinary non-magic file, if it isn't one already.
If filename specifies a magic file name, which programs outside Emacs cannot directly read or write, this copies the contents to an ordinary file and returns that file's name.
If filename is an ordinary file name, not magic, then this function does nothing and returns
nil.
This function returns the name of a directory that is not magic. It uses the directory part of filename if that is not magic. For a magic file name, it invokes the file name handler, which therefore decides what value to return.
This is useful for running a subprocess; every subprocess must have a non-magic directory to serve as its current directory, and this function is a good way to come up with one.
The variable format-alist defines a list of file formats,
which describe textual representations used in files for the data (text,
text-properties, and possibly other information) in an Emacs buffer.
Emacs performs format conversion if appropriate when reading and writing
files.
Each format definition is a list of this form:
(name doc-string regexp from-fn to-fn modify mode-fn)
Here is what the elements in a format definition mean:
A shell command is represented as a string; Emacs runs the command as a filter to perform the conversion.
If from-fn is a function, it is called with two arguments, begin and end, which specify the part of the buffer it should convert. It should convert the text by editing it in place. Since this can change the length of the text, from-fn should return the modified end position.
One responsibility of from-fn is to make sure that the beginning
of the file no longer matches regexp. Otherwise it is likely to
get called again.
If to-fn is a string, it is a shell command; Emacs runs the command as a filter to perform the conversion.
If to-fn is a function, it is called with two arguments, begin and end, which specify the part of the buffer it should convert. There are two ways it can do the conversion:
(position . string), where position is an
integer specifying the relative position in the text to be written, and
string is the annotation to add there. The list must be sorted in
order of position when to-fn returns it.
When write-region actually writes the text from the buffer to the
file, it intermixes the specified annotations at the corresponding
positions. All this takes place without modifying the buffer.
t if the encoding function modifies the buffer, and
nil if it works by returning a list of annotations.
The function insert-file-contents automatically recognizes file
formats when it reads the specified file. It checks the text of the
beginning of the file against the regular expressions of the format
definitions, and if it finds a match, it calls the decoding function for
that format. Then it checks all the known formats over again.
It keeps checking them until none of them is applicable.
Visiting a file, with find-file-noselect or the commands that use
it, performs conversion likewise (because it calls
insert-file-contents); it also calls the mode function for each
format that it decodes. It stores a list of the format names in the
buffer-local variable buffer-file-format.
This variable states the format of the visited file. More precisely, this is a list of the file format names that were decoded in the course of visiting the current buffer's file. It is always buffer-local in all buffers.
When write-region writes data into a file, it first calls the
encoding functions for the formats listed in buffer-file-format,
in the order of appearance in the list.
This command writes the current buffer contents into the file file in format format, and makes that format the default for future saves of the buffer. The argument format is a list of format names.
This command finds the file file, converting it according to format format. It also makes format the default if the buffer is saved later.
The argument format is a list of format names. If format is
nil, no conversion takes place. Interactively, typing just <RET> for format specifiesnil.
This command inserts the contents of file file, converting it according to format format. If beg and end are non-
nil, they specify which part of the file to read, as ininsert-file-contents(see Reading from Files).The return value is like what
insert-file-contentsreturns: a list of the absolute file name and the length of the data inserted (after conversion).The argument format is a list of format names. If format is
nil, no conversion takes place. Interactively, typing just <RET> for format specifiesnil.
This variable specifies the format to use for auto-saving. Its value is a list of format names, just like the value of
buffer-file-format; however, it is used instead ofbuffer-file-formatfor writing auto-save files. This variable is always buffer-local in all buffers.
Backup files and auto-save files are two methods by which Emacs tries to protect the user from the consequences of crashes or of the user's own errors. Auto-saving preserves the text from earlier in the current editing session; backup files preserve file contents prior to the current session.
A backup file is a copy of the old contents of a file you are editing. Emacs makes a backup file the first time you save a buffer into its visited file. Normally, this means that the backup file contains the contents of the file as it was before the current editing session. The contents of the backup file normally remain unchanged once it exists.
Backups are usually made by renaming the visited file to a new name. Optionally, you can specify that backup files should be made by copying the visited file. This choice makes a difference for files with multiple names; it also can affect whether the edited file remains owned by the original owner or becomes owned by the user editing it.
By default, Emacs makes a single backup file for each file edited. You can alternatively request numbered backups; then each new backup file gets a new name. You can delete old numbered backups when you don't want them any more, or Emacs can delete them automatically.
This function makes a backup of the file visited by the current buffer, if appropriate. It is called by
save-bufferbefore saving the buffer the first time.
This buffer-local variable indicates whether this buffer's file has been backed up on account of this buffer. If it is non-
nil, then the backup file has been written. Otherwise, the file should be backed up when it is next saved (if backups are enabled). This is a permanent local;kill-all-local-variablesdoes not alter it.
This variable determines whether or not to make backup files. If it is non-
nil, then Emacs creates a backup of each file when it is saved for the first time—provided thatbackup-inhibitedisnil(see below).The following example shows how to change the
make-backup-filesvariable only in the Rmail buffers and not elsewhere. Setting itnilstops Emacs from making backups of these files, which may save disk space. (You would put this code in your init file.)(add-hook 'rmail-mode-hook (function (lambda () (make-local-variable 'make-backup-files) (setq make-backup-files nil))))
This variable's value is a function to be called on certain occasions to decide whether a file should have backup files. The function receives one argument, a file name to consider. If the function returns
nil, backups are disabled for that file. Otherwise, the other variables in this section say whether and how to make backups.The default value is
normal-backup-enable-predicate, which checks for files intemporary-file-directoryandsmall-temporary-file-directory.
If this variable is non-
nil, backups are inhibited. It records the result of testingbackup-enable-predicateon the visited file name. It can also coherently be used by other mechanisms that inhibit backups based on which file is visited. For example, VC sets this variable non-nilto prevent making backups for files managed with a version control system.This is a permanent local, so that changing the major mode does not lose its value. Major modes should not set this variable—they should set
make-backup-filesinstead.
This variable's value is an alist of filename patterns and backup directory names. Each element looks like
(regexp . directory)Backups of files with names matching regexp will be made in directory. directory may be relative or absolute. If it is absolute, so that all matching files are backed up into the same directory, the file names in this directory will be the full name of the file backed up with all directory separators changed to ‘!’ to prevent clashes. This will not work correctly if your filesystem truncates the resulting name.
For the common case of all backups going into one directory, the alist should contain a single element pairing ‘"."’ with the appropriate directory name.
If this variable is
nil, or it fails to match a filename, the backup is made in the original file's directory.On MS-DOS filesystems without long names this variable is always ignored.
This variable's value is a function to use for making backups instead of the default
make-backup-file-name. A value of nil gives the defaultmake-backup-file-namebehaviour.This could be buffer-local to do something special for specific files. If you define it, you may need to change
backup-file-name-pandfile-name-sans-versionstoo.
There are two ways that Emacs can make a backup file:
The first method, renaming, is the default.
The variable backup-by-copying, if non-nil, says to use
the second method, which is to copy the original file and overwrite it
with the new buffer contents. The variable file-precious-flag,
if non-nil, also has this effect (as a sideline of its main
significance). See Saving Buffers.
If this variable is non-
nil, Emacs always makes backup files by copying.
The following two variables, when non-nil, cause the second
method to be used in certain special cases. They have no effect on the
treatment of files that don't fall into the special cases.
If this variable is non-
nil, Emacs makes backups by copying for files with multiple names (hard links).This variable is significant only if
backup-by-copyingisnil, since copying is always used when that variable is non-nil.
If this variable is non-
nil, Emacs makes backups by copying in cases where renaming would change either the owner or the group of the file.The value has no effect when renaming would not alter the owner or group of the file; that is, for files which are owned by the user and whose group matches the default for a new file created there by the user.
This variable is significant only if
backup-by-copyingisnil, since copying is always used when that variable is non-nil.
This variable, if non-
nil, specifies the same behavior asbackup-by-copying-when-mismatch, but only for certain user-id values: namely, those less than or equal to a certain number. You set this variable to that number.Thus, if you set
backup-by-copying-when-privileged-mismatchto 0, backup by copying is done for the superuser only, when necessary to prevent a change in the owner of the file.The default is 200.
If a file's name is foo, the names of its numbered backup versions are foo.~v~, for various integers v, like this: foo.~1~, foo.~2~, foo.~3~, ..., foo.~259~, and so on.
This variable controls whether to make a single non-numbered backup file or multiple numbered backups.
nil- Make numbered backups if the visited file already has numbered backups; otherwise, do not.
never- Do not make numbered backups.
- anything else
- Make numbered backups.
The use of numbered backups ultimately leads to a large number of backup versions, which must then be deleted. Emacs can do this automatically or it can ask the user whether to delete them.
The value of this variable is the number of newest versions to keep when a new numbered backup is made. The newly made backup is included in the count. The default value is 2.
The value of this variable is the number of oldest versions to keep when a new numbered backup is made. The default value is 2.
If there are backups numbered 1, 2, 3, 5, and 7, and both of these
variables have the value 2, then the backups numbered 1 and 2 are kept
as old versions and those numbered 5 and 7 are kept as new versions;
backup version 3 is excess. The function find-backup-file-name
(see Backup Names) is responsible for determining which backup
versions to delete, but does not delete them itself.
If this variable is
t, then saving a file deletes excess backup versions silently. If it isnil, that means to ask for confirmation before deleting excess backups. Otherwise, they are not deleted at all.
This variable specifies how many of the newest backup versions to keep in the Dired command . (
dired-clean-directory). That's the same thingkept-new-versionsspecifies when you make a new backup file. The default value is 2.
The functions in this section are documented mainly because you can customize the naming conventions for backup files by redefining them. If you change one, you probably need to change the rest.
This function returns a non-
nilvalue if filename is a possible name for a backup file. A file with the name filename need not exist; the function just checks the name.(backup-file-name-p "foo") => nil (backup-file-name-p "foo~") => 3The standard definition of this function is as follows:
(defun backup-file-name-p (file) "Return non-nil if FILE is a backup file \ name (numeric or not)..." (string-match "~\\'" file))Thus, the function returns a non-
nilvalue if the file name ends with a ‘~’. (We use a backslash to split the documentation string's first line into two lines in the text, but produce just one line in the string itself.)This simple expression is placed in a separate function to make it easy to redefine for customization.
This function returns a string that is the name to use for a non-numbered backup file for file filename. On Unix, this is just filename with a tilde appended.
The standard definition of this function, on most operating systems, is as follows:
(defun make-backup-file-name (file) "Create the non-numeric backup file name for FILE..." (concat file "~"))You can change the backup-file naming convention by redefining this function. The following example redefines
make-backup-file-nameto prepend a ‘.’ in addition to appending a tilde:(defun make-backup-file-name (filename) (expand-file-name (concat "." (file-name-nondirectory filename) "~") (file-name-directory filename))) (make-backup-file-name "backups.texi") => ".backups.texi~"Some parts of Emacs, including some Dired commands, assume that backup file names end with ‘~’. If you do not follow that convention, it will not cause serious problems, but these commands may give less-than-desirable results.
This function computes the file name for a new backup file for filename. It may also propose certain existing backup files for deletion.
find-backup-file-namereturns a list whose car is the name for the new backup file and whose cdr is a list of backup files whose deletion is proposed.Two variables,
kept-old-versionsandkept-new-versions, determine which backup versions should be kept. This function keeps those versions by excluding them from the cdr of the value. See Numbered Backups.In this example, the value says that ~rms/foo.~5~ is the name to use for the new backup file, and ~rms/foo.~3~ is an “excess” version that the caller should consider deleting now.
(find-backup-file-name "~rms/foo") => ("~rms/foo.~5~" "~rms/foo.~3~")
This function returns the name of the most recent backup file for filename, or
nilif that file has no backup files.Some file comparison commands use this function so that they can automatically compare a file with its most recent backup.
Emacs periodically saves all files that you are visiting; this is called auto-saving. Auto-saving prevents you from losing more than a limited amount of work if the system crashes. By default, auto-saves happen every 300 keystrokes, or after around 30 seconds of idle time. See Auto-Save, for information on auto-save for users. Here we describe the functions used to implement auto-saving and the variables that control them.
This buffer-local variable is the name of the file used for auto-saving the current buffer. It is
nilif the buffer should not be auto-saved.buffer-auto-save-file-name => "/xcssun/users/rms/lewis/#backups.texi#"
When used interactively without an argument, this command is a toggle switch: it turns on auto-saving of the current buffer if it is off, and vice versa. With an argument arg, the command turns auto-saving on if the value of arg is
t, a nonempty list, or a positive integer. Otherwise, it turns auto-saving off.
This function returns a non-
nilvalue if filename is a string that could be the name of an auto-save file. It assumes the usual naming convention for auto-save files: a name that begins and ends with hash marks (‘#’) is a possible auto-save file name. The argument filename should not contain a directory part.(make-auto-save-file-name) => "/xcssun/users/rms/lewis/#backups.texi#" (auto-save-file-name-p "#backups.texi#") => 0 (auto-save-file-name-p "backups.texi") => nilThe standard definition of this function is as follows:
(defun auto-save-file-name-p (filename) "Return non-nil if FILENAME can be yielded by..." (string-match "^#.*#$" filename))This function exists so that you can customize it if you wish to change the naming convention for auto-save files. If you redefine it, be sure to redefine the function
make-auto-save-file-namecorrespondingly.
This function returns the file name to use for auto-saving the current buffer. This is just the file name with hash marks (‘#’) prepended and appended to it. This function does not look at the variable
auto-save-visited-file-name(described below); callers of this function should check that variable first.(make-auto-save-file-name) => "/xcssun/users/rms/lewis/#backups.texi#"The standard definition of this function is as follows:
(defun make-auto-save-file-name () "Return file name to use for auto-saves \ of current buffer.." (if buffer-file-name (concat (file-name-directory buffer-file-name) "#" (file-name-nondirectory buffer-file-name) "#") (expand-file-name (concat "#%" (buffer-name) "#"))))This exists as a separate function so that you can redefine it to customize the naming convention for auto-save files. Be sure to change
auto-save-file-name-pin a corresponding way.
If this variable is non-
nil, Emacs auto-saves buffers in the files they are visiting. That is, the auto-save is done in the same file that you are editing. Normally, this variable isnil, so auto-save files have distinct names that are created bymake-auto-save-file-name.When you change the value of this variable, the new value does not take effect in an existing buffer until the next time auto-save mode is reenabled in it. If auto-save mode is already enabled, auto-saves continue to go in the same file name until
auto-save-modeis called again.
This function returns
tif the current buffer has been auto-saved since the last time it was read in or saved.
This function marks the current buffer as auto-saved. The buffer will not be auto-saved again until the buffer text is changed again. The function returns
nil.
The value of this variable specifies how often to do auto-saving, in terms of number of input events. Each time this many additional input events are read, Emacs does auto-saving for all buffers in which that is enabled.
The value of this variable is the number of seconds of idle time that should cause auto-saving. Each time the user pauses for this long, Emacs does auto-saving for all buffers in which that is enabled. (If the current buffer is large, the specified timeout is multiplied by a factor that increases as the size increases; for a million-byte buffer, the factor is almost 4.)
If the value is zero or nil, then auto-saving is not done as a result of idleness, only after a certain number of input events as specified by
auto-save-interval.
If this variable is non-
nil, buffers that are visiting files have auto-saving enabled by default. Otherwise, they do not.
This function auto-saves all buffers that need to be auto-saved. It saves all buffers for which auto-saving is enabled and that have been changed since the previous auto-save.
Normally, if any buffers are auto-saved, a message that says ‘Auto-saving...’ is displayed in the echo area while auto-saving is going on. However, if no-message is non-
nil, the message is inhibited.If current-only is non-
nil, only the current buffer is auto-saved.
This function deletes the current buffer's auto-save file if
delete-auto-save-filesis non-nil. It is called every time a buffer is saved.
This variable is used by the function
delete-auto-save-file-if-necessary. If it is non-nil, Emacs deletes auto-save files when a true save is done (in the visited file). This saves disk space and unclutters your directory.
This function adjusts the current buffer's auto-save file name if the visited file name has changed. It also renames an existing auto-save file. If the visited file name has not changed, this function does nothing.
The value of this buffer-local variable is the length of the current buffer, when it was last read in, saved, or auto-saved. This is used to detect a substantial decrease in size, and turn off auto-saving in response.
If it is −1, that means auto-saving is temporarily shut off in this buffer due to a substantial decrease in size. Explicitly saving the buffer stores a positive value in this variable, thus reenabling auto-saving. Turning auto-save mode off or on also updates this variable, so that the substantial decrease in size is forgotten.
This variable (if non-
nil) specifies a file for recording the names of all the auto-save files. Each time Emacs does auto-saving, it writes two lines into this file for each buffer that has auto-saving enabled. The first line gives the name of the visited file (it's empty if the buffer has none), and the second gives the name of the auto-save file.When Emacs exits normally, it deletes this file; if Emacs crashes, you can look in the file to find all the auto-save files that might contain work that was otherwise lost. The
recover-sessioncommand uses this file to find them.The default name for this file specifies your home directory and starts with ‘.saves-’. It also contains the Emacs process id and the host name.
After Emacs reads your init file, it initializes
auto-save-list-file-name(if you have not already set it non-nil) based on this prefix, adding the host name and process ID. If you set this tonilin your init file, then Emacs does not initializeauto-save-list-file-name.
If you have made extensive changes to a file and then change your mind
about them, you can get rid of them by reading in the previous version
of the file with the revert-buffer command. See Reverting a Buffer.
This command replaces the buffer text with the text of the visited file on disk. This action undoes all changes since the file was visited or saved.
By default, if the latest auto-save file is more recent than the visited file, and the argument ignore-auto is
nil,revert-bufferasks the user whether to use that auto-save instead. When you invoke this command interactively, ignore-auto istif there is no numeric prefix argument; thus, the interactive default is not to check the auto-save file.Normally,
revert-bufferasks for confirmation before it changes the buffer; but if the argument noconfirm is non-nil,revert-bufferdoes not ask for confirmation.Reverting tries to preserve marker positions in the buffer by using the replacement feature of
insert-file-contents. If the buffer contents and the file contents are identical before the revert operation, reverting preserves all the markers. If they are not identical, reverting does change the buffer; in that case, it preserves the markers in the unchanged text (if any) at the beginning and end of the buffer. Preserving any additional markers would be problematical.
You can customize how revert-buffer does its work by setting
the variables described in the rest of this section.
This variable holds a list of files that should be reverted without query. The value is a list of regular expressions. If the visited file name matches one of these regular expressions, and the file has changed on disk but the buffer is not modified, then
revert-bufferreverts the file without asking the user for confirmation.
Some major modes customize revert-buffer by making
buffer-local bindings for these variables:
The value of this variable is the function to use to revert this buffer. If non-
nil, it is called as a function with no arguments to do the work of reverting. If the value isnil, reverting works the usual way.Modes such as Dired mode, in which the text being edited does not consist of a file's contents but can be regenerated in some other fashion, can give this variable a buffer-local value that is a function to regenerate the contents.
The value of this variable, if non-
nil, specifies the function to use to insert the updated contents when reverting this buffer. The function receives two arguments: first the file name to use; second,tif the user has asked to read the auto-save file.The reason for a mode to set this variable instead of
revert-buffer-functionis to avoid duplicating or replacing the rest of whatrevert-bufferdoes: asking for confirmation, clearing the undo list, deciding the proper major mode, and running the hooks listed below.
This normal hook is run by
revert-bufferbefore inserting the modified contents—but only ifrevert-buffer-functionisnil.
This normal hook is run by
revert-bufferafter inserting the modified contents—but only ifrevert-buffer-functionisnil.
A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents of files that are being visited; there may also be buffers that are not visiting files. While several buffers may exist at one time, only one buffer is designated the current buffer at any time. Most editing commands act on the contents of the current buffer. Each buffer, including the current buffer, may or may not be displayed in any windows.
A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents of files that are being visited; there may also be buffers that are not visiting files. Although several buffers normally exist, only one buffer is designated the current buffer at any time. Most editing commands act on the contents of the current buffer. Each buffer, including the current buffer, may or may not be displayed in any windows.
Buffers in Emacs editing are objects that have distinct names and hold text that can be edited. Buffers appear to Lisp programs as a special data type. You can think of the contents of a buffer as a string that you can extend; insertions and deletions may occur in any part of the buffer. See Text.
A Lisp buffer object contains numerous pieces of information. Some of this information is directly accessible to the programmer through variables, while other information is accessible only through special-purpose functions. For example, the visited file name is directly accessible through a variable, while the value of point is accessible only through a primitive function.
Buffer-specific information that is directly accessible is stored in
buffer-local variable bindings, which are variable values that are
effective only in a particular buffer. This feature allows each buffer
to override the values of certain variables. Most major modes override
variables such as fill-column or comment-column in this
way. For more information about buffer-local variables and functions
related to them, see Buffer-Local Variables.
For functions and variables related to visiting files in buffers, see Visiting Files and Saving Buffers. For functions and variables related to the display of buffers in windows, see Buffers and Windows.
There are, in general, many buffers in an Emacs session. At any time, one of them is designated as the current buffer. This is the buffer in which most editing takes place, because most of the primitives for examining or changing text in a buffer operate implicitly on the current buffer (see Text). Normally the buffer that is displayed on the screen in the selected window is the current buffer, but this is not always so: a Lisp program can temporarily designate any buffer as current in order to operate on its contents, without changing what is displayed on the screen.
The way to designate a current buffer in a Lisp program is by calling
set-buffer. The specified buffer remains current until a new one
is designated.
When an editing command returns to the editor command loop, the
command loop designates the buffer displayed in the selected window as
current, to prevent confusion: the buffer that the cursor is in when
Emacs reads a command is the buffer that the command will apply to.
(See Command Loop.) Therefore, set-buffer is not the way to
switch visibly to a different buffer so that the user can edit it. For
that, you must use the functions described in Displaying Buffers.
Note: Lisp functions that change to a different current buffer
should not depend on the command loop to set it back afterwards.
Editing commands written in Emacs Lisp can be called from other programs
as well as from the command loop; it is convenient for the caller if
the subroutine does not change which buffer is current (unless, of
course, that is the subroutine's purpose). Therefore, you should
normally use set-buffer within a save-current-buffer or
save-excursion (see Excursions) form that will restore the
current buffer when your function is done. Here is an example, the
code for the command append-to-buffer (with the documentation
string abridged):
(defun append-to-buffer (buffer start end)
"Append to specified buffer the text of the region.
..."
(interactive "BAppend to buffer: \nr")
(let ((oldbuf (current-buffer)))
(save-current-buffer
(set-buffer (get-buffer-create buffer))
(insert-buffer-substring oldbuf start end))))
This function binds a local variable to record the current buffer, and
then save-current-buffer arranges to make it current again.
Next, set-buffer makes the specified buffer current. Finally,
insert-buffer-substring copies the string from the original
current buffer to the specified (and now current) buffer.
If the buffer appended to happens to be displayed in some window, the next redisplay will show how its text has changed. Otherwise, you will not see the change immediately on the screen. The buffer becomes current temporarily during the execution of the command, but this does not cause it to be displayed.
If you make local bindings (with let or function arguments) for
a variable that may also have buffer-local bindings, make sure that the
same buffer is current at the beginning and at the end of the local
binding's scope. Otherwise you might bind it in one buffer and unbind
it in another! There are two ways to do this. In simple cases, you may
see that nothing ever changes the current buffer within the scope of the
binding. Otherwise, use save-current-buffer or
save-excursion to make sure that the buffer current at the
beginning is current again whenever the variable is unbound.
Do not rely on using set-buffer to change the current buffer
back, because that won't do the job if a quit happens while the wrong
buffer is current. Here is what not to do:
(let (buffer-read-only
(obuf (current-buffer)))
(set-buffer ...)
...
(set-buffer obuf))
Using save-current-buffer, as shown here, handles quitting,
errors, and throw, as well as ordinary evaluation.
(let (buffer-read-only)
(save-current-buffer
(set-buffer ...)
...))
This function returns the current buffer.
(current-buffer) => #<buffer buffers.texi>
This function makes buffer-or-name the current buffer. This does not display the buffer in any window, so the user cannot necessarily see the buffer. But Lisp programs will now operate on it.
This function returns the buffer identified by buffer-or-name. An error is signaled if buffer-or-name does not identify an existing buffer.
The
save-current-buffermacro saves the identity of the current buffer, evaluates the body forms, and finally restores that buffer as current. The return value is the value of the last form in body. The current buffer is restored even in case of an abnormal exit viathrowor error (see Nonlocal Exits).If the buffer that used to be current has been killed by the time of exit from
save-current-buffer, then it is not made current again, of course. Instead, whichever buffer was current just before exit remains current.
The
with-current-buffermacro saves the identity of the current buffer, makes buffer current, evaluates the body forms, and finally restores the buffer. The return value is the value of the last form in body. The current buffer is restored even in case of an abnormal exit viathrowor error (see Nonlocal Exits).
The
with-temp-buffermacro evaluates the body forms with a temporary buffer as the current buffer. It saves the identity of the current buffer, creates a temporary buffer and makes it current, evaluates the body forms, and finally restores the previous current buffer while killing the temporary buffer.The return value is the value of the last form in body. You can return the contents of the temporary buffer by using
(buffer-string)as the last form.The current buffer is restored even in case of an abnormal exit via
throwor error (see Nonlocal Exits).
See also with-temp-file in Writing to Files.
Each buffer has a unique name, which is a string. Many of the functions that work on buffers accept either a buffer or a buffer name as an argument. Any argument called buffer-or-name is of this sort, and an error is signaled if it is neither a string nor a buffer. Any argument called buffer must be an actual buffer object, not a name.
Buffers that are ephemeral and generally uninteresting to the user
have names starting with a space, so that the list-buffers and
buffer-menu commands don't mention them. A name starting with
space also initially disables recording undo information; see
Undo.
This function returns the name of buffer as a string. If buffer is not supplied, it defaults to the current buffer.
If
buffer-namereturnsnil, it means that buffer has been killed. See Killing Buffers.(buffer-name) => "buffers.texi" (setq foo (get-buffer "temp")) => #<buffer temp> (kill-buffer foo) => nil (buffer-name foo) => nil foo => #<killed buffer>
This function renames the current buffer to newname. An error is signaled if newname is not a string, or if there is already a buffer with that name. The function returns newname.
Ordinarily,
rename-buffersignals an error if newname is already in use. However, if unique is non-nil, it modifies newname to make a name that is not in use. Interactively, you can make unique non-nilwith a numeric prefix argument. (This is how the commandrename-uniquelyis implemented.)
This function returns the buffer specified by buffer-or-name. If buffer-or-name is a string and there is no buffer with that name, the value is
nil. If buffer-or-name is a buffer, it is returned as given; that is not very useful, so the argument is usually a name. For example:(setq b (get-buffer "lewis")) => #<buffer lewis> (get-buffer b) => #<buffer lewis> (get-buffer "Frazzle-nots") => nilSee also the function
get-buffer-createin Creating Buffers.
This function returns a name that would be unique for a new buffer—but does not create the buffer. It starts with starting-name, and produces a name not currently in use for any buffer by appending a number inside of ‘<...>’.
If the optional second argument ignore is non-
nil, it should be a string; it makes a difference if it is a name in the sequence of names to be tried. That name will be considered acceptable, if it is tried, even if a buffer with that name exists. Thus, if buffers named ‘foo’, ‘foo<2>’, ‘foo<3>’ and ‘foo<4>’ exist,(generate-new-buffer-name "foo") => "foo<5>" (generate-new-buffer-name "foo" "foo<3>") => "foo<3>" (generate-new-buffer-name "foo" "foo<6>") => "foo<5>"See the related function
generate-new-bufferin Creating Buffers.
The buffer file name is the name of the file that is visited in
that buffer. When a buffer is not visiting a file, its buffer file name
is nil. Most of the time, the buffer name is the same as the
nondirectory part of the buffer file name, but the buffer file name and
the buffer name are distinct and can be set independently.
See Visiting Files.
This function returns the absolute file name of the file that buffer is visiting. If buffer is not visiting any file,
buffer-file-namereturnsnil. If buffer is not supplied, it defaults to the current buffer.(buffer-file-name (other-buffer)) => "/usr/user/lewis/manual/files.texi"
This buffer-local variable contains the name of the file being visited in the current buffer, or
nilif it is not visiting a file. It is a permanent local variable, unaffected bykill-all-local-variables.buffer-file-name => "/usr/user/lewis/manual/buffers.texi"It is risky to change this variable's value without doing various other things. Normally it is better to use
set-visited-file-name(see below); some of the things done there, such as changing the buffer name, are not strictly necessary, but others are essential to avoid confusing Emacs.
This buffer-local variable holds the truename of the file visited in the current buffer, or
nilif no file is visited. It is a permanent local, unaffected bykill-all-local-variables. See Truenames.
This buffer-local variable holds the file number and directory device number of the file visited in the current buffer, or
nilif no file or a nonexistent file is visited. It is a permanent local, unaffected bykill-all-local-variables.The value is normally a list of the form
(filenum devnum). This pair of numbers uniquely identifies the file among all files accessible on the system. See the functionfile-attributes, in File Attributes, for more information about them.
This function returns the buffer visiting file filename. If there is no such buffer, it returns
nil. The argument filename, which must be a string, is expanded (see File Name Expansion), then compared against the visited file names of all live buffers.(get-file-buffer "buffers.texi") => #<buffer buffers.texi>In unusual circumstances, there can be more than one buffer visiting the same file name. In such cases, this function returns the first such buffer in the buffer list.
If filename is a non-empty string, this function changes the name of the file visited in the current buffer to filename. (If the buffer had no visited file, this gives it one.) The next time the buffer is saved it will go in the newly-specified file. This command marks the buffer as modified, since it does not (as far as Emacs knows) match the contents of filename, even if it matched the former visited file.
If filename is
nilor the empty string, that stands for “no visited file”. In this case,set-visited-file-namemarks the buffer as having no visited file.Normally, this function asks the user for confirmation if the specified file already exists. If no-query is non-
nil, that prevents asking this question.If along-with-file is non-
nil, that means to assume that the former visited file has been renamed to filename.When the function
set-visited-file-nameis called interactively, it prompts for filename in the minibuffer.
This buffer-local variable specifies a string to display in a buffer listing where the visited file name would go, for buffers that don't have a visited file name. Dired buffers use this variable.
Emacs keeps a flag called the modified flag for each buffer, to
record whether you have changed the text of the buffer. This flag is
set to t whenever you alter the contents of the buffer, and
cleared to nil when you save it. Thus, the flag shows whether
there are unsaved changes. The flag value is normally shown in the mode
line (see Mode Line Variables), and controls saving (see Saving Buffers) and auto-saving (see Auto-Saving).
Some Lisp programs set the flag explicitly. For example, the function
set-visited-file-name sets the flag to t, because the text
does not match the newly-visited file, even if it is unchanged from the
file formerly visited.
The functions that modify the contents of buffers are described in Text.
This function returns
tif the buffer buffer has been modified since it was last read in from a file or saved, ornilotherwise. If buffer is not supplied, the current buffer is tested.
This function marks the current buffer as modified if flag is non-
nil, or as unmodified if the flag isnil.Another effect of calling this function is to cause unconditional redisplay of the mode line for the current buffer. In fact, the function
force-mode-line-updateworks by doing this:(set-buffer-modified-p (buffer-modified-p))
This command marks the current buffer as unmodified, and not needing to be saved. With prefix arg, it marks the buffer as modified, so that it will be saved at the next suitable occasion.
Don't use this function in programs, since it prints a message in the echo area; use
set-buffer-modified-p(above) instead.
This function returns buffer's modification-count. This is a counter that increments every time the buffer is modified. If buffer is
nil(or omitted), the current buffer is used.
Suppose that you visit a file and make changes in its buffer, and meanwhile the file itself is changed on disk. At this point, saving the buffer would overwrite the changes in the file. Occasionally this may be what you want, but usually it would lose valuable information. Emacs therefore checks the file's modification time using the functions described below before saving the file.
This function compares what buffer has recorded for the modification time of its visited file against the actual modification time of the file as recorded by the operating system. The two should be the same unless some other process has written the file since Emacs visited or saved it.
The function returns
tif the last actual modification time and Emacs's recorded modification time are the same,nilotherwise.
This function clears out the record of the last modification time of the file being visited by the current buffer. As a result, the next attempt to save this buffer will not complain of a discrepancy in file modification times.
This function is called in
set-visited-file-nameand other exceptional places where the usual test to avoid overwriting a changed file should not be done.
This function returns the buffer's recorded last file modification time, as a list of the form
(high.low). (This is the same format thatfile-attributesuses to return time values; see File Attributes.)
This function updates the buffer's record of the last modification time of the visited file, to the value specified by time if time is not
nil, and otherwise to the last modification time of the visited file.If time is not
nil, it should have the form(high.low)or(high low), in either case containing two integers, each of which holds 16 bits of the time.This function is useful if the buffer was not read from the file normally, or if the file itself has been changed for some known benign reason.
This function is used to ask a user how to proceed after an attempt to modify an obsolete buffer visiting file filename. An obsolete buffer is an unmodified buffer for which the associated file on disk is newer than the last save-time of the buffer. This means some other program has probably altered the file.
Depending on the user's answer, the function may return normally, in which case the modification of the buffer proceeds, or it may signal a
file-supersessionerror with data(filename), in which case the proposed buffer modification is not allowed.This function is called automatically by Emacs on the proper occasions. It exists so you can customize Emacs by redefining it. See the file userlock.el for the standard definition.
See also the file locking mechanism in File Locks.
If a buffer is read-only, then you cannot change its contents, although you may change your view of the contents by scrolling and narrowing.
Read-only buffers are used in two kinds of situations:
Here, the purpose is to inform the user that editing the buffer with the aim of saving it in the file may be futile or undesirable. The user who wants to change the buffer text despite this can do so after clearing the read-only flag with C-x C-q.
The special commands of these modes bind buffer-read-only to
nil (with let) or bind inhibit-read-only to
t around the places where they themselves change the text.
This buffer-local variable specifies whether the buffer is read-only. The buffer is read-only if this variable is non-
nil.
If this variable is non-
nil, then read-only buffers and read-only characters may be modified. Read-only characters in a buffer are those that have non-nilread-onlyproperties (either text properties or overlay properties). See Special Properties, for more information about text properties. See Overlays, for more information about overlays and their properties.If
inhibit-read-onlyist, allread-onlycharacter properties have no effect. Ifinhibit-read-onlyis a list, thenread-onlycharacter properties have no effect if they are members of the list (comparison is done witheq).
This command changes whether the current buffer is read-only. It is intended for interactive use; do not use it in programs. At any given point in a program, you should know whether you want the read-only flag on or off; so you can set
buffer-read-onlyexplicitly to the proper value,tornil.
This function signals a
buffer-read-onlyerror if the current buffer is read-only. See Interactive Call, for another way to signal an error if the current buffer is read-only.
The buffer list is a list of all live buffers. Creating a
buffer adds it to this list, and killing a buffer excises it. The order
of the buffers in the list is based primarily on how recently each
buffer has been displayed in the selected window. Buffers move to the
front of the list when they are selected and to the end when they are
buried (see bury-buffer, below). Several functions, notably
other-buffer, use this ordering. A buffer list displayed for the
user also follows this order.
In addition to the fundamental Emacs buffer list, each frame has its
own version of the buffer list, in which the buffers that have been
selected in that frame come first, starting with the buffers most
recently selected in that frame. (This order is recorded in
frame's buffer-list frame parameter; see Window Frame Parameters.) The buffers that were never selected in frame come
afterward, ordered according to the fundamental Emacs buffer list.
This function returns the buffer list, including all buffers, even those whose names begin with a space. The elements are actual buffers, not their names.
If frame is a frame, this returns frame's buffer list. If frame is
nil, the fundamental Emacs buffer list is used: all the buffers appear in order of most recent selection, regardless of which frames they were selected in.(buffer-list) => (#<buffer buffers.texi> #<buffer *Minibuf-1*> #<buffer buffer.c> #<buffer *Help*> #<buffer TAGS>) ;; Note that the name of the minibuffer ;; begins with a space! (mapcar (function buffer-name) (buffer-list)) => ("buffers.texi" " *Minibuf-1*" "buffer.c" "*Help*" "TAGS")
The list that buffer-list returns is constructed specifically
by buffer-list; it is not an internal Emacs data structure, and
modifying it has no effect on the order of buffers. If you want to
change the order of buffers in the frame-independent buffer list, here
is an easy way:
(defun reorder-buffer-list (new-list)
(while new-list
(bury-buffer (car new-list))
(setq new-list (cdr new-list))))
With this method, you can specify any order for the list, but there is no danger of losing a buffer or adding something that is not a valid live buffer.
To change the order or value of a frame's buffer list, set the frame's
buffer-list frame parameter with modify-frame-parameters
(see Parameter Access).
This function returns the first buffer in the buffer list other than buffer. Usually this is the buffer selected most recently (in frame frame or else the currently selected frame, see Input Focus), aside from buffer. Buffers whose names start with a space are not considered at all.
If buffer is not supplied (or if it is not a buffer), then
other-bufferreturns the first buffer in the selected frame's buffer list that is not now visible in any window in a visible frame.If frame has a non-
nilbuffer-predicateparameter, thenother-bufferuses that predicate to decide which buffers to consider. It calls the predicate once for each buffer, and if the value isnil, that buffer is ignored. See Window Frame Parameters.If visible-ok is
nil,other-bufferavoids returning a buffer visible in any window on any visible frame, except as a last resort. If visible-ok is non-nil, then it does not matter whether a buffer is displayed somewhere or not.If no suitable buffer exists, the buffer ‘*scratch*’ is returned (and created, if necessary).
This function puts buffer-or-name at the end of the buffer list, without changing the order of any of the other buffers on the list. This buffer therefore becomes the least desirable candidate for
other-bufferto return.
bury-bufferoperates on each frame'sbuffer-listparameter as well as the frame-independent Emacs buffer list; therefore, the buffer that you bury will come last in the value of(buffer-listframe)and in the value of(buffer-list nil).If buffer-or-name is
nilor omitted, this means to bury the current buffer. In addition, if the buffer is displayed in the selected window, this switches to some other buffer (obtained usingother-buffer) in the selected window. But if the buffer is displayed in some other window, it remains displayed there.To replace a buffer in all the windows that display it, use
replace-buffer-in-windows. See Buffers and Windows.
This section describes the two primitives for creating buffers.
get-buffer-create creates a buffer if it finds no existing buffer
with the specified name; generate-new-buffer always creates a new
buffer and gives it a unique name.
Other functions you can use to create buffers include
with-output-to-temp-buffer (see Temporary Displays) and
create-file-buffer (see Visiting Files). Starting a
subprocess can also create a buffer (see Processes).
This function returns a buffer named name. It returns an existing buffer with that name, if one exists; otherwise, it creates a new buffer. The buffer does not become the current buffer—this function does not change which buffer is current.
An error is signaled if name is not a string.
(get-buffer-create "foo") => #<buffer foo>The major mode for the new buffer is set to Fundamental mode. The variable
default-major-modeis handled at a higher level. See Auto Major Mode.
This function returns a newly created, empty buffer, but does not make it current. If there is no buffer named name, then that is the name of the new buffer. If that name is in use, this function adds suffixes of the form ‘<n>’ to name, where n is an integer. It tries successive integers starting with 2 until it finds an available name.
An error is signaled if name is not a string.
(generate-new-buffer "bar") => #<buffer bar> (generate-new-buffer "bar") => #<buffer bar<2>> (generate-new-buffer "bar") => #<buffer bar<3>>The major mode for the new buffer is set to Fundamental mode. The variable
default-major-modeis handled at a higher level. See Auto Major Mode.See the related function
generate-new-buffer-namein Buffer Names.
Killing a buffer makes its name unknown to Emacs and makes its text space available for other use.
The buffer object for the buffer that has been killed remains in
existence as long as anything refers to it, but it is specially marked
so that you cannot make it current or display it. Killed buffers retain
their identity, however; if you kill two distinct buffers, they remain
distinct according to eq although both are dead.
If you kill a buffer that is current or displayed in a window, Emacs automatically selects or displays some other buffer instead. This means that killing a buffer can in general change the current buffer. Therefore, when you kill a buffer, you should also take the precautions associated with changing the current buffer (unless you happen to know that the buffer being killed isn't current). See Current Buffer.
If you kill a buffer that is the base buffer of one or more indirect buffers, the indirect buffers are automatically killed as well.
The buffer-name of a killed buffer is nil. You can use
this feature to test whether a buffer has been killed:
(defun buffer-killed-p (buffer)
"Return t if BUFFER is killed."
(not (buffer-name buffer)))
This function kills the buffer buffer-or-name, freeing all its memory for other uses or to be returned to the operating system. It returns
nil.Any processes that have this buffer as the
process-bufferare sent theSIGHUPsignal, which normally causes them to terminate. (The basic meaning ofSIGHUPis that a dialup line has been disconnected.) See Deleting Processes.If the buffer is visiting a file and contains unsaved changes,
kill-bufferasks the user to confirm before the buffer is killed. It does this even if not called interactively. To prevent the request for confirmation, clear the modified flag before callingkill-buffer. See Buffer Modification.Killing a buffer that is already dead has no effect.
(kill-buffer "foo.unchanged") => nil (kill-buffer "foo.changed") ---------- Buffer: Minibuffer ---------- Buffer foo.changed modified; kill anyway? (yes or no) yes ---------- Buffer: Minibuffer ---------- => nil
After confirming unsaved changes,
kill-buffercalls the functions in the listkill-buffer-query-functions, in order of appearance, with no arguments. The buffer being killed is the current buffer when they are called. The idea of this feature is that these functions will ask for confirmation from the user. If any of them returnsnil,kill-bufferspares the buffer's life.
This is a normal hook run by
kill-bufferafter asking all the questions it is going to ask, just before actually killing the buffer. The buffer to be killed is current when the hook functions run. See Hooks.
This variable, if non-
nilin a particular buffer, tellssave-buffers-kill-emacsandsave-some-buffersto offer to save that buffer, just as they offer to save file-visiting buffers. The variablebuffer-offer-saveautomatically becomes buffer-local when set for any reason. See Buffer-Local Variables.
An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link among files. The base buffer may not itself be an indirect buffer.
The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. This includes the text properties as well as the characters themselves.
In all other respects, the indirect buffer and its base buffer are completely separate. They have different names, different values of point, different narrowing, different markers and overlays (though inserting or deleting text in either buffer relocates the markers and overlays for both), different major modes, and different buffer-local variables.
An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually saves the base buffer.
Killing an indirect buffer has no effect on its base buffer. Killing the base buffer effectively kills the indirect buffer in that it cannot ever again be the current buffer.
This creates an indirect buffer named name whose base buffer is base-buffer. The argument base-buffer may be a buffer or a string.
If base-buffer is an indirect buffer, its base buffer is used as the base for the new buffer.
This function returns the base buffer of buffer. If buffer is not indirect, the value is
nil. Otherwise, the value is another buffer, which is never an indirect buffer.
Emacs buffers are implemented using an invisible gap to make insertion and deletion faster. Insertion works by filling in part of the gap, and deletion adds to the gap. Of course, this means that the gap must first be moved to the locus of the insertion or deletion. Emacs moves the gap only when you try to insert or delete. This is why your first editing command in one part of a large buffer, after previously editing in another far-away part, sometimes involves a noticeable delay.
This mechanism works invisibly, and Lisp code should never be affected by the gap's current location, but these functions are available for getting information about the gap status.
This chapter describes most of the functions and variables related to Emacs windows. See Display, for information on how text is displayed in windows.
A window in Emacs is the physical area of the screen in which a buffer is displayed. The term is also used to refer to a Lisp object that represents that screen area in Emacs Lisp. It should be clear from the context which is meant.
Emacs groups windows into frames. A frame represents an area of screen available for Emacs to use. Each frame always contains at least one window, but you can subdivide it vertically or horizontally into multiple nonoverlapping Emacs windows.
In each frame, at any time, one and only one window is designated as
selected within the frame. The frame's cursor appears in that
window. At any time, one frame is the selected frame; and the window
selected within that frame is the selected window. The selected
window's buffer is usually the current buffer (except when
set-buffer has been used). See Current Buffer.
For practical purposes, a window exists only while it is displayed in a frame. Once removed from the frame, the window is effectively deleted and should not be used, even though there may still be references to it from other Lisp objects. Restoring a saved window configuration is the only way for a window no longer on the screen to come back to life. (See Deleting Windows.)
Each window has the following attributes:
Users create multiple windows so they can look at several buffers at once. Lisp libraries use multiple windows for a variety of reasons, but most often to display related information. In Rmail, for example, you can move through a summary buffer in one window while the other window shows messages one at a time as they are reached.
The meaning of “window” in Emacs is similar to what it means in the context of general-purpose window systems such as X, but not identical. The X Window System places X windows on the screen; Emacs uses one or more X windows as frames, and subdivides them into Emacs windows. When you use Emacs on a character-only terminal, Emacs treats the whole terminal screen as one frame.
Most window systems support arbitrarily located overlapping windows. In contrast, Emacs windows are tiled; they never overlap, and together they fill the whole screen or frame. Because of the way in which Emacs creates new windows and resizes them, not all conceivable tilings of windows on an Emacs frame are actually possible. See Splitting Windows, and Size of Window.
See Display, for information on how the contents of the window's buffer are displayed in the window.
The functions described here are the primitives used to split a window
into two windows. Two higher level functions sometimes split a window,
but not always: pop-to-buffer and display-buffer
(see Displaying Buffers).
The functions described here do not accept a buffer as an argument. The two “halves” of the split window initially display the same buffer previously visible in the window that was split.
This function splits window into two windows. The original window window remains the selected window, but occupies only part of its former screen area. The rest is occupied by a newly created window which is returned as the value of this function.
If horizontal is non-
nil, then window splits into two side by side windows. The original window window keeps the leftmost size columns, and gives the rest of the columns to the new window. Otherwise, it splits into windows one above the other, and window keeps the upper size lines and gives the rest of the lines to the new window. The original window is therefore the left-hand or upper of the two, and the new window is the right-hand or lower.If window is omitted or
nil, then the selected window is split. If size is omitted ornil, then window is divided evenly into two parts. (If there is an odd line, it is allocated to the new window.) Whensplit-windowis called interactively, all its arguments arenil.The following example starts with one window on a screen that is 50 lines high by 80 columns wide; then the window is split.
(setq w (selected-window)) => #<window 8 on windows.texi> (window-edges) ; Edges in order: => (0 0 80 50) ; left--top--right--bottom ;; Returns window created (setq w2 (split-window w 15)) => #<window 28 on windows.texi> (window-edges w2) => (0 15 80 50) ; Bottom window; ; top is line 15 (window-edges w) => (0 0 80 15) ; Top windowThe screen looks like this:
__________ | | line 0 | w | |__________| | | line 15 | w2 | |__________| line 50 column 0 column 80Next, the top window is split horizontally:
(setq w3 (split-window w 35 t)) => #<window 32 on windows.texi> (window-edges w3) => (35 0 80 15) ; Left edge at column 35 (window-edges w) => (0 0 35 15) ; Right edge at column 35 (window-edges w2) => (0 15 80 50) ; Bottom window unchangedNow, the screen looks like this:
column 35 __________ | | | line 0 | w | w3 | |___|______| | | line 15 | w2 | |__________| line 50 column 0 column 80Normally, Emacs indicates the border between two side-by-side windows with a scroll bar (see Scroll Bars) or ‘|’ characters. The display table can specify alternative border characters; see Display Tables.
This function splits the selected window into two windows, one above the other, leaving the upper of the two windows selected, with size lines. (If size is negative, then the lower of the two windows gets − size lines and the upper window gets the rest, but the upper window is still the one selected.)
This function splits the selected window into two windows side-by-side, leaving the selected window with size columns.
This function is basically an interface to
split-window. You could define a simplified version of the function like this:(defun split-window-horizontally (&optional arg) "Split selected window into two windows, side by side..." (interactive "P") (let ((size (and arg (prefix-numeric-value arg)))) (and size (< size 0) (setq size (+ (window-width) size))) (split-window nil size t)))
This function returns non-
nilif there is only one window. The argument no-mini, if non-nil, means don't count the minibuffer even if it is active; otherwise, the minibuffer window is included, if active, in the total number of windows, which is compared against one.The argument all-frames specifies which frames to consider. Here are the possible values and their meanings:
nil- Count the windows in the selected frame, plus the minibuffer used by that frame even if it lies in some other frame.
t- Count all windows in all existing frames.
visible- Count all windows in all visible frames.
- 0
- Count all windows in all visible or iconified frames.
- anything else
- Count precisely the windows in the selected frame, and no others.
A window remains visible on its frame unless you delete it by calling certain functions that delete windows. A deleted window cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a window aside from restoring a saved window configuration (see Window Configurations). Restoring a window configuration also deletes any windows that aren't part of that configuration.
When you delete a window, the space it took up is given to one adjacent sibling.
This function returns
nilif window is deleted, andtotherwise.Warning: Erroneous information or fatal errors may result from using a deleted window as if it were live.
This function removes window from display, and returns
nil. If window is omitted, then the selected window is deleted. An error is signaled if there is only one window whendelete-windowis called.
This function makes window the only window on its frame, by deleting the other windows in that frame. If window is omitted or
nil, then the selected window is used by default.The return value is
nil.
This function deletes all windows showing buffer. If there are no windows showing buffer, it does nothing.
delete-windows-onoperates frame by frame. If a frame has several windows showing different buffers, then those showing buffer are removed, and the others expand to fill the space. If all windows in some frame are showing buffer (including the case where there is only one window), then the frame reverts to having a single window showing another buffer chosen withother-buffer. See The Buffer List.The argument frame controls which frames to operate on. This function does not use it in quite the same way as the other functions which scan all windows; specifically, the values
tandnilhave the opposite of their meanings in other functions. Here are the full details:
- If it is
nil, operate on all frames.- If it is
t, operate on the selected frame.- If it is
visible, operate on all visible frames.- If it is 0, operate on all visible or iconified frames.
- If it is a frame, operate on that frame.
This function always returns
nil.
When a window is selected, the buffer in the window becomes the current buffer, and the cursor will appear in it.
This function returns the selected window. This is the window in which the cursor appears and to which many commands apply.
This function makes window the selected window. The cursor then appears in window (on redisplay). The buffer being displayed in window is immediately designated the current buffer.
The return value is window.
(setq w (next-window)) (select-window w) => #<window 65 on windows.texi>
This macro records the selected window, executes forms in sequence, then restores the earlier selected window, unless it is no longer alive.
This macro does not save or restore anything about the sizes, arrangement or contents of windows; therefore, if the forms change them, the change persists.
Each frame, at any time, has a window selected within the frame. This macro saves only the selected window; it does not save anything about other frames. If the forms select some other frame and alter the window selected within it, the change persists.
The following functions choose one of the windows on the screen, offering various criteria for the choice.
This function returns the window least recently “used” (that is, selected). The selected window is always the most recently used window.
The selected window can be the least recently used window if it is the only window. A newly created window becomes the least recently used window until it is selected. A minibuffer window is never a candidate.
The argument frame controls which windows are considered.
- If it is
nil, consider windows on the selected frame.- If it is
t, consider windows on all frames.- If it is
visible, consider windows on all visible frames.- If it is 0, consider windows on all visible or iconified frames.
- If it is a frame, consider windows on that frame.
This function returns the window with the largest area (height times width). If there are no side-by-side windows, then this is the window with the most lines. A minibuffer window is never a candidate.
If there are two windows of the same size, then the function returns the window that is first in the cyclic ordering of windows (see following section), starting from the selected window.
The argument frame controls which set of windows to consider. See
get-lru-window, above.
This function returns a window satisfying predicate. It cycles through all visible windows using
walk-windows(see Cyclic Window Ordering), calling predicate on each one one of them with that window as its argument. The function returns the first window for which predicate returns a non-nilvalue; if that never happens, it returns default.The optional arguments minibuf and all-frames specify the set of windows to include in the scan. See the description of
next-windowin Cyclic Window Ordering, for details.
When you use the command C-x o (other-window) to select
the next window, it moves through all the windows on the screen in a
specific cyclic order. For any given configuration of windows, this
order never varies. It is called the cyclic ordering of windows.
This ordering generally goes from top to bottom, and from left to right. But it may go down first or go right first, depending on the order in which the windows were split.
If the first split was vertical (into windows one above each other), and then the subwindows were split horizontally, then the ordering is left to right in the top of the frame, and then left to right in the next lower part of the frame, and so on. If the first split was horizontal, the ordering is top to bottom in the left part, and so on. In general, within each set of siblings at any level in the window tree, the order is left to right, or top to bottom.
This function returns the window following window in the cyclic ordering of windows. This is the window that C-x o would select if typed when window is selected. If window is the only window visible, then this function returns window. If omitted, window defaults to the selected window.
The value of the argument minibuf determines whether the minibuffer is included in the window order. Normally, when minibuf is
nil, the minibuffer is included if it is currently active; this is the behavior of C-x o. (The minibuffer window is active while the minibuffer is in use. See Minibuffers.)If minibuf is
t, then the cyclic ordering includes the minibuffer window even if it is not active.If minibuf is neither
tnornil, then the minibuffer window is not included even if it is active.The argument all-frames specifies which frames to consider. Here are the possible values and their meanings:
nil- Consider all the windows in window's frame, plus the minibuffer used by that frame even if it lies in some other frame.
t- Consider all windows in all existing frames.
visible- Consider all windows in all visible frames. (To get useful results, you must ensure window is in a visible frame.)
- 0
- Consider all windows in all visible or iconified frames.
- anything else
- Consider precisely the windows in window's frame, and no others.
This example assumes there are two windows, both displaying the buffer ‘windows.texi’:
(selected-window) => #<window 56 on windows.texi> (next-window (selected-window)) => #<window 52 on windows.texi> (next-window (next-window (selected-window))) => #<window 56 on windows.texi>
This function returns the window preceding window in the cyclic ordering of windows. The other arguments specify which windows to include in the cycle, as in
next-window.
This function selects the countth following window in the cyclic order. If count is negative, then it moves back −count windows in the cycle, rather than forward. It returns
nil.The argument all-frames has the same meaning as in
next-window, but the minibuf argument ofnext-windowis always effectivelynil.In an interactive call, count is the numeric prefix argument.
This function cycles through all windows, calling
proconce for each window with the window as its sole argument.The optional arguments minibuf and all-frames specify the set of windows to include in the scan. See
next-window, above, for details.
This function returns a list of the windows on frame, starting with window. If frame is
nilor omitted, the selected frame is used instead; if window isnilor omitted, the selected window is used instead.The value of minibuf determines if the minibuffer window will be included in the result list. If minibuf is
t, the minibuffer window will be included, even if it isn't active. If minibuf isnilor omitted, the minibuffer window will only be included in the list if it is active. If minibuf is neithernilnort, the minibuffer window is not included, whether or not it is active.
This section describes low-level functions to examine windows or to display buffers in windows in a precisely controlled fashion. See Displaying Buffers, for related functions that find a window to use and specify a buffer for it. The functions described there are easier to use than these, but they employ heuristics in choosing or creating a window; use these functions when you need complete control.
This function makes window display buffer-or-name as its contents. It returns
nil. This is the fundamental primitive for changing which buffer is displayed in a window, and all ways of doing that call this function.(set-window-buffer (selected-window) "foo") => nil
This function returns the buffer that window is displaying. If window is omitted, this function returns the buffer for the selected window.
(window-buffer) => #<buffer windows.texi>
This function returns a window currently displaying buffer-or-name, or
nilif there is none. If there are several such windows, then the function returns the first one in the cyclic ordering of windows, starting from the selected window. See Cyclic Window Ordering.The argument all-frames controls which windows to consider.
- If it is
nil, consider windows on the selected frame.- If it is
t, consider windows on all frames.- If it is
visible, consider windows on all visible frames.- If it is 0, consider windows on all visible or iconified frames.
- If it is a frame, consider windows on that frame.
This function returns a list of all the windows currently displaying buffer-or-name.
The two optional arguments work like the optional arguments of
next-window(see Cyclic Window Ordering); they are not like the single optional argument ofget-buffer-window. Perhaps we should changeget-buffer-windowin the future to make it compatible with the other functions.The argument all-frames controls which windows to consider.
- If it is
nil, consider windows on the selected frame.- If it is
t, consider windows on all frames.- If it is
visible, consider windows on all visible frames.- If it is 0, consider windows on all visible or iconified frames.
- If it is a frame, consider windows on that frame.
This variable records the time at which a buffer was last made visible in a window. It is always local in each buffer; each time
set-window-bufferis called, it sets this variable to(current-time)in the specified buffer (see Time of Day). When a buffer is first created,buffer-display-timestarts out with the valuenil.
In this section we describe convenient functions that choose a window
automatically and use it to display a specified buffer. These functions
can also split an existing window in certain circumstances. We also
describe variables that parameterize the heuristics used for choosing a
window.
See Buffers and Windows, for
low-level functions that give you more precise control. All of these
functions work by calling set-window-buffer.
Do not use the functions in this section in order to make a buffer
current so that a Lisp program can access or modify it; they are too
drastic for that purpose, since they change the display of buffers in
windows, which would be gratuitous and surprise the user. Instead, use
set-buffer and save-current-buffer (see Current Buffer), which designate buffers as current for programmed access
without affecting the display of buffers in windows.
This function makes buffer-or-name the current buffer, and also displays the buffer in the selected window. This means that a human can see the buffer and subsequent keyboard commands will apply to it. Contrast this with
set-buffer, which makes buffer-or-name the current buffer but does not display it in the selected window. See Current Buffer.If buffer-or-name does not identify an existing buffer, then a new buffer by that name is created. The major mode for the new buffer is set according to the variable
default-major-mode. See Auto Major Mode.Normally the specified buffer is put at the front of the buffer list (both the selected frame's buffer list and the frame-independent buffer list). This affects the operation of
other-buffer. However, if norecord is non-nil, this is not done. See The Buffer List.The
switch-to-bufferfunction is often used interactively, as the binding of C-x b. It is also used frequently in programs. It always returnsnil.
This function makes buffer-or-name the current buffer and displays it in a window not currently selected. It then selects that window. The handling of the buffer is the same as in
switch-to-buffer.The currently selected window is absolutely never used to do the job. If it is the only window, then it is split to make a distinct window for this purpose. If the selected window is already displaying the buffer, then it continues to do so, but another window is nonetheless found to display it in as well.
This function updates the buffer list just like
switch-to-bufferunless norecord is non-nil.
This function makes buffer-or-name the current buffer and switches to it in some window, preferably not the window previously selected. The “popped-to” window becomes the selected window within its frame.
If the variable
pop-up-framesis non-nil,pop-to-bufferlooks for a window in any visible frame already displaying the buffer; if there is one, it returns that window and makes it be selected within its frame. If there is none, it creates a new frame and displays the buffer in it.If
pop-up-framesisnil, thenpop-to-bufferoperates entirely within the selected frame. (If the selected frame has just a minibuffer,pop-to-bufferoperates within the most recently selected frame that was not just a minibuffer.)If the variable
pop-up-windowsis non-nil, windows may be split to create a new window that is different from the original window. For details, see Choosing Window.If other-window is non-
nil,pop-to-bufferfinds or creates another window even if buffer-or-name is already visible in the selected window. Thus buffer-or-name could end up displayed in two windows. On the other hand, if buffer-or-name is already displayed in the selected window and other-window isnil, then the selected window is considered sufficient display for buffer-or-name, so that nothing needs to be done.All the variables that affect
display-bufferaffectpop-to-bufferas well. See Choosing Window.If buffer-or-name is a string that does not name an existing buffer, a buffer by that name is created. The major mode for the new buffer is set according to the variable
default-major-mode. See Auto Major Mode.This function updates the buffer list just like
switch-to-bufferunless norecord is non-nil.
This function replaces buffer with some other buffer in all windows displaying it. The other buffer used is chosen with
other-buffer. In the usual applications of this function, you don't care which other buffer is used; you just want to make sure that buffer is no longer displayed.This function returns
nil.
This section describes the basic facility that chooses a window to
display a buffer in—display-buffer. All the higher-level
functions and commands use this subroutine. Here we describe how to use
display-buffer and how to customize it.
This command makes buffer-or-name appear in some window, like
pop-to-buffer, but it does not select that window and does not make the buffer current. The identity of the selected window is unaltered by this function.If not-this-window is non-
nil, it means to display the specified buffer in a window other than the selected one, even if it is already on display in the selected window. This can cause the buffer to appear in two windows at once. Otherwise, if buffer-or-name is already being displayed in any window, that is good enough, so this function does nothing.
display-bufferreturns the window chosen to display buffer-or-name.If the argument frame is non-
nil, it specifies which frames to check when deciding whether the buffer is already displayed. If the buffer is already displayed in some window on one of these frames,display-buffersimply returns that window. Here are the possible values of frame:
- If it is
nil, consider windows on the selected frame.- If it is
t, consider windows on all frames.- If it is
visible, consider windows on all visible frames.- If it is 0, consider windows on all visible or iconified frames.
- If it is a frame, consider windows on that frame.
Precisely how
display-bufferfinds or creates a window depends on the variables described below.
If this variable is non-
nil,display-buffersearches existing frames for a window displaying the buffer. If the buffer is already displayed in a window in some frame,display-buffermakes the frame visible and raises it, to use that window. If the buffer is not already displayed, or ifdisplay-buffer-reuse-framesisnil,display-buffer's behavior is determined by other variables, described below.
This variable controls whether
display-buffermakes new windows. If it is non-niland there is only one window, then that window is split. If it isnil, thendisplay-bufferdoes not split the single window, but uses it whole.
This variable determines when
display-buffermay split a window, if there are multiple windows.display-bufferalways splits the largest window if it has at least this many lines. If the largest window is not this tall, it is split only if it is the sole window andpop-up-windowsis non-nil.
This variable determines if
display-buffershould even out window heights if the buffer gets displayed in an existing window, above or beneath another existing window. Ifeven-window-heightsist, the default, window heights will be evened out. Ifeven-window-heightsisnil, the orginal window heights will be left alone.
This variable controls whether
display-buffermakes new frames. If it is non-nil,display-bufferlooks for an existing window already displaying the desired buffer, on any visible frame. If it finds one, it returns that window. Otherwise it makes a new frame. The variablespop-up-windowsandsplit-height-thresholddo not matter ifpop-up-framesis non-nil.If
pop-up-framesisnil, thendisplay-buffereither splits a window or reuses one.See Frames, for more information.
This variable specifies how to make a new frame if
pop-up-framesis non-nil.Its value should be a function of no arguments. When
display-buffermakes a new frame, it does so by calling that function, which should return a frame. The default value of the variable is a function that creates a frame using parameters frompop-up-frame-alist.
This variable holds an alist specifying frame parameters used when
display-buffermakes a new frame. See Frame Parameters, for more information about frame parameters.
A list of buffer names for buffers that should be displayed specially. If the buffer's name is in this list,
display-bufferhandles the buffer specially.By default, special display means to give the buffer a dedicated frame.
If an element is a list, instead of a string, then the car of the list is the buffer name, and the rest of the list says how to create the frame. There are two possibilities for the rest of the list. It can be an alist, specifying frame parameters, or it can contain a function and arguments to give to it. (The function's first argument is always the buffer to be displayed; the arguments from the list come after that.)
A list of regular expressions that specify buffers that should be displayed specially. If the buffer's name matches any of the regular expressions in this list,
display-bufferhandles the buffer specially.By default, special display means to give the buffer a dedicated frame.
If an element is a list, instead of a string, then the car of the list is the regular expression, and the rest of the list says how to create the frame. See above, under
special-display-buffer-names.
This variable holds the function to call to display a buffer specially. It receives the buffer as an argument, and should return the window in which it is displayed.
The default value of this variable is
special-display-popup-frame.
This function makes buffer visible in a frame of its own. If buffer is already displayed in a window in some frame, it makes the frame visible and raises it, to use that window. Otherwise, it creates a frame that will be dedicated to buffer.
If args is an alist, it specifies frame parameters for the new frame.
If args is a list whose car is a symbol, then
(carargs)is called as a function to actually create and set up the frame; it is called with buffer as first argument, and(cdrargs)as additional arguments.This function always uses an existing window displaying buffer, whether or not it is in a frame of its own; but if you set up the above variables in your init file, before buffer was created, then presumably the window was previously made by this function.
This variable holds frame parameters for
special-display-popup-frameto use when it creates a frame.
A list of buffer names for buffers that should be displayed in the selected window. If the buffer's name is in this list,
display-bufferhandles the buffer by switching to it in the selected window.
A list of regular expressions that specify buffers that should be displayed in the selected window. If the buffer's name matches any of the regular expressions in this list,
display-bufferhandles the buffer by switching to it in the selected window.
This variable is the most flexible way to customize the behavior of
display-buffer. If it is non-nil, it should be a function thatdisplay-buffercalls to do the work. The function should accept two arguments, the same two arguments thatdisplay-bufferreceived. It should choose or create a window, display the specified buffer, and then return the window.This hook takes precedence over all the other options and hooks described above.
A window can be marked as “dedicated” to its buffer. Then
display-buffer will not try to use that window to display any
other buffer.
This function returns
tif window is marked as dedicated; otherwisenil.
This function marks window as dedicated if flag is non-
nil, and nondedicated otherwise.
Each window has its own value of point, independent of the value of point in other windows displaying the same buffer. This makes it useful to have multiple windows showing one buffer.
As far as the user is concerned, point is where the cursor is, and when the user switches to another buffer, the cursor jumps to the position of point in that buffer.
This function returns the current position of point in window. For a nonselected window, this is the value point would have (in that window's buffer) if that window were selected. If window is
nil, the selected window is used.When window is the selected window and its buffer is also the current buffer, the value returned is the same as point in that buffer.
Strictly speaking, it would be more correct to return the “top-level” value of point, outside of any
save-excursionforms. But that value is hard to find.
This function positions point in window at position position in window's buffer.
Each window contains a marker used to keep track of a buffer position that specifies where in the buffer display should start. This position is called the display-start position of the window (or just the start). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line.
This function returns the display-start position of window window. If window is
nil, the selected window is used. For example,(window-start) => 7058When you create a window, or display a different buffer in it, the display-start position is set to a display-start position recently used for the same buffer, or 1 if the buffer doesn't have any.
Redisplay updates the window-start position (if you have not specified it explicitly since the previous redisplay)—for example, to make sure point appears on the screen. Nothing except redisplay automatically changes the window-start position; if you move point, do not expect the window-start position to change in response until after the next redisplay.
For a realistic example of using
window-start, see the description ofcount-linesin Text Lines.
This function returns the position of the end of the display in window window. If window is
nil, the selected window is used.Simply changing the buffer text or moving point does not update the value that
window-endreturns. The value is updated only when Emacs redisplays and redisplay completes without being preempted.If the last redisplay of window was preempted, and did not finish, Emacs does not know the position of the end of display in that window. In that case, this function returns
nil.If update is non-
nil,window-endalways returns an up-to-date value for where the window ends, based on the currentwindow-startvalue. If the saved value is valid,window-endreturns that; otherwise it computes the correct value by scanning the buffer text.Even if update is non-
nil,window-enddoes not attempt to scroll the display if point has moved off the screen, the way real redisplay would do. It does not alter thewindow-startvalue. In effect, it reports where the displayed text will end if scrolling is not required.
This function sets the display-start position of window to position in window's buffer. It returns position.
The display routines insist that the position of point be visible when a buffer is displayed. Normally, they change the display-start position (that is, scroll the window) whenever necessary to make point visible. However, if you specify the start position with this function using
nilfor noforce, it means you want display to start at position even if that would put the location of point off the screen. If this does place point off screen, the display routines move point to the left margin on the middle line in the window.For example, if point is 1 and you set the start of the window to 2, then point would be “above” the top of the window. The display routines will automatically move point if it is still 1 when redisplay occurs. Here is an example:
;; Here is what ‘foo’ looks like before executing ;; theset-window-startexpression. ---------- Buffer: foo ---------- -!-This is the contents of buffer foo. 2 3 4 5 6 ---------- Buffer: foo ---------- (set-window-start (selected-window) (1+ (window-start))) => 2 ;; Here is what ‘foo’ looks like after executing ;; theset-window-startexpression. ---------- Buffer: foo ---------- his is the contents of buffer foo. 2 3 -!-4 5 6 ---------- Buffer: foo ----------If noforce is non-
nil, and position would place point off screen at the next redisplay, then redisplay computes a new window-start position that works well with point, and thus position is not used.
This function returns
tif position is within the range of text currently visible on the screen in window. It returnsnilif position is scrolled vertically or horizontally out of view. Locations that are partially obscured are not considered visible unless partially is non-nil. The argument position defaults to the current position of point in window; window, to the selected window.Here is an example:
(or (pos-visible-in-window-p (point) (selected-window)) (recenter 0))
Textual scrolling means moving the text up or down though a
window. It works by changing the value of the window's display-start
location. It may also change the value of window-point to keep
point on the screen.
Textual scrolling was formerly called “vertical scrolling,” but we changed its name to distinguish it from the new vertical fractional scrolling feature (see Vertical Scrolling).
In the commands scroll-up and scroll-down, the directions
“up” and “down” refer to the motion of the text in the buffer at which
you are looking through the window. Imagine that the text is
written on a long roll of paper and that the scrolling commands move the
paper up and down. Thus, if you are looking at text in the middle of a
buffer and repeatedly call scroll-down, you will eventually see
the beginning of the buffer.
Some people have urged that the opposite convention be used: they imagine that the window moves over text that remains in place. Then “down” commands would take you to the end of the buffer. This view is more consistent with the actual relationship between windows and the text in the buffer, but it is less like what the user sees. The position of a window on the terminal does not move, and short scrolling commands clearly move the text up or down on the screen. We have chosen names that fit the user's point of view.
The textual scrolling functions (aside from
scroll-other-window) have unpredictable results if the current
buffer is different from the buffer that is displayed in the selected
window. See Current Buffer.
This function scrolls the text in the selected window upward count lines. If count is negative, scrolling is actually downward.
If count is
nil(or omitted), then the length of scroll isnext-screen-context-lineslines less than the usable height of the window (not counting its mode line).
scroll-upreturnsnil.
This function scrolls the text in the selected window downward count lines. If count is negative, scrolling is actually upward.
If count is omitted or
nil, then the length of the scroll isnext-screen-context-lineslines less than the usable height of the window (not counting its mode line).
scroll-downreturnsnil.
This function scrolls the text in another window upward count lines. Negative values of count, or
nil, are handled as inscroll-up.You can specify which buffer to scroll by setting the variable
other-window-scroll-bufferto a buffer. If that buffer isn't already displayed,scroll-other-windowdisplays it in some window.When the selected window is the minibuffer, the next window is normally the one at the top left corner. You can specify a different window to scroll, when the minibuffer is selected, by setting the variable
minibuffer-scroll-window. This variable has no effect when any other window is selected. See Minibuffer Misc.When the minibuffer is active, it is the next window if the selected window is the one at the bottom right corner. In this case,
scroll-other-windowattempts to scroll the minibuffer. If the minibuffer contains just one line, it has nowhere to scroll to, so the line reappears after the echo area momentarily displays the message “Beginning of buffer”.
If this variable is non-
nil, it tellsscroll-other-windowwhich buffer to scroll.
This option specifies the size of the scroll margin—a minimum number of lines between point and the top or bottom of a window. Whenever point gets within this many lines of the top or bottom of the window, the window scrolls automatically (if possible) to move point out of the margin, closer to the center of the window.
This variable controls how scrolling is done automatically when point moves off the screen (or into the scroll margin). If the value is zero, then redisplay scrolls the text to center point vertically in the window. If the value is a positive integer n, then redisplay scrolls the window up to n lines in either direction, if that will bring point back into view. Otherwise, it centers point. The default value is zero.
The value of this variable should be either
nilor a fraction f between 0 and 1. If it is a fraction, that specifies where on the screen to put point when scrolling down. More precisely, when a window scrolls down because point is above the window start, the new start position is chosen to put point f part of the window height from the top. The larger f, the more aggressive the scrolling.A value of
nilis equivalent to .5, since its effect is to center point. This variable automatically becomes buffer-local when set in any fashion.
Likewise, for scrolling up. The value, f, specifies how far point should be placed from the bottom of the window; thus, as with
scroll-up-aggressively, a larger value scrolls more aggressively.
This variable is an older variant of
scroll-conservatively. The difference is that it if its value is n, that permits scrolling only by precisely n lines, not a smaller number. This feature does not work withscroll-margin. The default value is zero.
If this option is non-
nil, the scroll functions move point so that the vertical position of the cursor is unchanged, when that is possible.
The value of this variable is the number of lines of continuity to retain when scrolling by full screens. For example,
scroll-upwith an argument ofnilscrolls so that this many lines at the bottom of the window appear instead at the top. The default value is2.
This function scrolls the selected window to put the text where point is located at a specified vertical position within the window.
If count is a nonnegative number, it puts the line containing point count lines down from the top of the window. If count is a negative number, then it counts upward from the bottom of the window, so that −1 stands for the last usable line in the window. If count is a non-
nillist, then it stands for the line in the middle of the window.If count is
nil,recenterputs the line containing point in the middle of the window, then clears and redisplays the entire selected frame.When
recenteris called interactively, count is the raw prefix argument. Thus, typing C-u as the prefix sets the count to a non-nillist, while typing C-u 4 sets count to 4, which positions the current line four lines from the top.With an argument of zero,
recenterpositions the current line at the top of the window. This action is so handy that some people make a separate key binding to do this. For example,(defun line-to-top-of-window () "Scroll current line to top of window. Replaces three keystroke sequence C-u 0 C-l." (interactive) (recenter 0)) (global-set-key [kp-multiply] 'line-to-top-of-window)
Vertical fractional scrolling means shifting the image in the window up or down by a specified multiple or fraction of a line. Starting in Emacs 21, each window has a vertical scroll position, which is a number, never less than zero. It specifies how far to raise the contents of the window. Raising the window contents generally makes all or part of some lines disappear off the top, and all or part of some other lines appear at the bottom. The usual value is zero.
The vertical scroll position is measured in units of the normal line height, which is the height of the default font. Thus, if the value is .5, that means the window contents are scrolled up half the normal line height. If it is 3.3, that means the window contents are scrolled up somewhat over three times the normal line height.
What fraction of a line the vertical scrolling covers, or how many lines, depends on what the lines contain. A value of .5 could scroll a line whose height is very short off the screen, while a value of 3.3 could scroll just part of the way through a tall line or an image.
This function returns the current vertical scroll position of window, If window is
nil, the selected window is used.(window-vscroll) => 0
This function sets window's vertical scroll position to lines. The argument lines should be zero or positive; if not, it is taken as zero.
The actual vertical scroll position must always correspond to an integral number of pixels, so the value you specify is rounded accordingly.
The return value is the result of this rounding.
(set-window-vscroll (selected-window) 1.2) => 1.13
Horizontal scrolling means shifting the image in the window left or right by a specified multiple of the normal character width. Each window has a vertical scroll position, which is a number, never less than zero. It specifies how far to shift the contents left. Shifting the window contents left generally makes all or part of some characters disappear off the left, and all or part of some other characters appear at the right. The usual value is zero.
The horizontal scroll position is measured in units of the normal character width, which is the width of space in the default font. Thus, if the value is 5, that means the window contents are scrolled left by 5 times the normal character width. How many characters actually disappear off to the left depends on their width, and could vary from line to line.
Because we read from side to side in the “inner loop”, and from top to bottom in the “outer loop”, the effect of horizontal scrolling is not like that of textual or vertical scrolling. Textual scrolling involves selection of a portion of text to display, and vertical scrolling moves the window contents contiguously; but horizontal scrolling causes part of each line to go off screen.
Usually, no horizontal scrolling is in effect; then the leftmost column is at the left edge of the window. In this state, scrolling to the right is meaningless, since there is no data to the left of the edge to be revealed by it; so this is not allowed. Scrolling to the left is allowed; it scrolls the first columns of text off the edge of the window and can reveal additional columns on the right that were truncated before. Once a window has a nonzero amount of leftward horizontal scrolling, you can scroll it back to the right, but only so far as to reduce the net horizontal scroll to zero. There is no limit to how far left you can scroll, but eventually all the text will disappear off the left edge.
In Emacs 21, redisplay automatically alters the horizontal scrolling
of a window as necessary to ensure that point is always visible, if
automatic-hscrolling is set. However, you can still set the
horizontal scrolling value explicitly. The value you specify serves as
a lower bound for automatic scrolling, i.e. automatic scrolling
will not scroll a window to a column less than the specified one.
This function scrolls the selected window count columns to the left (or to the right if count is negative). The default for count is the window width, minus 2.
The return value is the total amount of leftward horizontal scrolling in effect after the change—just like the value returned by
window-hscroll(below).
This function scrolls the selected window count columns to the right (or to the left if count is negative). The default for count is the window width, minus 2.
The return value is the total amount of leftward horizontal scrolling in effect after the change—just like the value returned by
window-hscroll(below).Once you scroll a window as far right as it can go, back to its normal position where the total leftward scrolling is zero, attempts to scroll any farther right have no effect.
This function returns the total leftward horizontal scrolling of window—the number of columns by which the text in window is scrolled left past the left margin.
The value is never negative. It is zero when no horizontal scrolling has been done in window (which is usually the case).
If window is
nil, the selected window is used.(window-hscroll) => 0 (scroll-left 5) => 5 (window-hscroll) => 5
This function sets the number of columns from the left margin that window is scrolled from the value of columns. The argument columns should be zero or positive; if not, it is taken as zero. Fractional values of columns are not supported at present.
The value returned is columns.
(set-window-hscroll (selected-window) 10) => 10
Here is how you can determine whether a given position position is off the screen due to horizontal scrolling:
(defun hscroll-on-screen (window position)
(save-excursion
(goto-char position)
(and
(>= (- (current-column) (window-hscroll window)) 0)
(< (- (current-column) (window-hscroll window))
(window-width window)))))
An Emacs window is rectangular, and its size information consists of the height (the number of lines) and the width (the number of character positions in each line). The mode line is included in the height. But the width does not count the scroll bar or the column of ‘|’ characters that separates side-by-side windows.
The following three functions return size information about a window:
This function returns the number of lines in window, including its mode line. If window fills its entire frame, this is typically one less than the value of
frame-heighton that frame (since the last line is always reserved for the minibuffer).If window is
nil, the function uses the selected window.(window-height) => 23 (split-window-vertically) => #<window 4 on windows.texi> (window-height) => 11
This function returns the number of columns in window. If window fills its entire frame, this is the same as the value of
frame-widthon that frame. The width does not include the window's scroll bar or the column of ‘|’ characters that separates side-by-side windows.If window is
nil, the function uses the selected window.(window-width) => 80
This function returns a list of the edge coordinates of window. If window is
nil, the selected window is used.The order of the list is
(left top right bottom), all elements relative to 0, 0 at the top left corner of the frame. The element right of the value is one more than the rightmost column used by window, and bottom is one more than the bottommost row used by window and its mode-line.If a window has a scroll bar, the right edge value includes the width of the scroll bar. Otherwise, if the window has a neighbor on the right, its right edge value includes the width of the separator line between the window and that neighbor. Since the width of the window does not include this separator, the width does not usually equal the difference between the right and left edges.
Here is the result obtained on a typical 24-line terminal with just one window:
(window-edges (selected-window)) => (0 0 80 23)The bottom edge is at line 23 because the last line is the echo area.
If window is at the upper left corner of its frame, then bottom is the same as the value of
(window-height), right is almost the same as the value of(window-width), and top and left are zero. For example, the edges of the following window are ‘0 0 8 5’. Assuming that the frame has more than 8 columns, the last column of the window (column 7) holds a border rather than text. The last row (row 4) holds the mode line, shown here with ‘xxxxxxxxx’.0 _______ 0 | | | | | | | | xxxxxxxxx 4 7In the following example, let's suppose that the frame is 7 columns wide. Then the edges of the left window are ‘0 0 4 3’ and the edges of the right window are ‘4 0 8 3’.
___ ___ | | | | | | xxxxxxxxx 0 34 7
The window size functions fall into two classes: high-level commands that change the size of windows and low-level functions that access window size. Emacs does not permit overlapping windows or gaps between windows, so resizing one window affects other windows.
This function makes the selected window size lines taller, stealing lines from neighboring windows. It takes the lines from one window at a time until that window is used up, then takes from another. If a window from which lines are stolen shrinks below
window-min-heightlines, that window disappears.If horizontal is non-
nil, this function makes window wider by size columns, stealing columns instead of lines. If a window from which columns are stolen shrinks belowwindow-min-widthcolumns, that window disappears.If the requested size would exceed that of the window's frame, then the function makes the window occupy the entire height (or width) of the frame.
If there are various other windows from which lines or columns can be stolen, and some of them specify fixed size (using
window-size-fixed, see below), they are left untouched while other windows are “robbed.” If it would be necessary to alter the size of a fixed-size window,enlarge-windowgets an error instead.If size is negative, this function shrinks the window by −size lines or columns. If that makes the window smaller than the minimum size (
window-min-heightandwindow-min-width),enlarge-windowdeletes the window.
enlarge-windowreturnsnil.
This function makes the selected window columns wider. It could be defined as follows:
(defun enlarge-window-horizontally (columns) (enlarge-window columns t))
This function is like
enlarge-windowbut negates the argument size, making the selected window smaller by giving lines (or columns) to the other windows. If the window shrinks belowwindow-min-heightorwindow-min-width, then it disappears.If size is negative, the window is enlarged by −size lines or columns.
This function makes the selected window columns narrower. It could be defined as follows:
(defun shrink-window-horizontally (columns) (shrink-window columns t))
This command shrinks window to be as small as possible while still showing the full contents of its buffer—but not less than
window-min-heightlines. If window is not given, it defaults to the selected window.However, the command does nothing if the window is already too small to display the whole text of the buffer, or if part of the contents are currently scrolled off screen, or if the window is not the full width of its frame, or if the window is the only window in its frame.
If this variable is non-
nil, in any given buffer, then the size of any window displaying the buffer remains fixed unless you explicitly change it or Emacs has no other choice. (This feature is new in Emacs 21.)If the value is
height, then only the window's height is fixed; if the value iswidth, then only the window's width is fixed. Any other non-nilvalue fixes both the width and the height.The usual way to use this variable is to give it a buffer-local value in a particular buffer. That way, the windows (but usually there is only one) displaying that buffer have fixed size.
Explicit size-change functions such as
enlarge-windowget an error if they would have to change a window size which is fixed. Therefore, when you want to change the size of such a window, you should bindwindow-size-fixedtonil, like this:(let ((window-size-fixed nil)) (enlarge-window 10))Note that changing the frame size will change the size of a fixed-size window, if there is no other alternative.
The following two variables constrain the window-size-changing functions to a minimum height and width.
The value of this variable determines how short a window may become before it is automatically deleted. Making a window smaller than
window-min-heightautomatically deletes it, and no window may be created shorter than this. The absolute minimum height is two (allowing one line for the mode line, and one line for the buffer display). Actions that change window sizes reset this variable to two if it is less than two. The default value is 4.
The value of this variable determines how narrow a window may become before it is automatically deleted. Making a window smaller than
window-min-widthautomatically deletes it, and no window may be created narrower than this. The absolute minimum width is one; any value below that is ignored. The default value is 10.
This section describes how to relate screen coordinates to windows.
This function returns the window containing the specified cursor position in the frame frame. The coordinates x and y are measured in characters and count from the top left corner of the frame. If they are out of range,
window-atreturnsnil.If you omit frame, the selected frame is used.
This function checks whether a particular frame position falls within the window window.
The argument coordinates is a cons cell of the form
(x.y). The coordinates x and y are measured in characters, and count from the top left corner of the screen or frame.The value returned by
coordinates-in-window-pis non-nilif the coordinates are inside window. The value also indicates what part of the window the position is in, as follows:
(relx.rely)- The coordinates are inside window. The numbers relx and rely are the equivalent window-relative coordinates for the specified position, counting from 0 at the top left corner of the window.
mode-line- The coordinates are in the mode line of window.
header-line- The coordinates are in the header line of window.
vertical-line- The coordinates are in the vertical line between window and its neighbor to the right. This value occurs only if the window doesn't have a scroll bar; positions in a scroll bar are considered outside the window for these purposes.
nil- The coordinates are not in any part of window.
The function
coordinates-in-window-pdoes not require a frame as argument because it always uses the frame that window is on.
A window configuration records the entire layout of one frame—all windows, their sizes, which buffers they contain, what part of each buffer is displayed, and the values of point and the mark. You can bring back an entire previous layout by restoring a window configuration previously saved.
If you want to record all frames instead of just one, use a frame configuration instead of a window configuration. See Frame Configurations.
This function returns a new object representing frame's current window configuration, including the number of windows, their sizes and current buffers, which window is the selected window, and for each window the displayed buffer, the display-start position, and the positions of point and the mark. It also includes the values of
window-min-height,window-min-widthandminibuffer-scroll-window. An exception is made for point in the current buffer, whose value is not saved.If frame is omitted, the selected frame is used.
This function restores the configuration of windows and buffers as specified by configuration, for the frame that configuration was created for.
The argument configuration must be a value that was previously returned by
current-window-configuration. This configuration is restored in the frame from which configuration was made, whether that frame is selected or not. This always counts as a window size change and triggers execution of thewindow-size-change-functions(see Window Hooks), becauseset-window-configurationdoesn't know how to tell whether the new configuration actually differs from the old one.If the frame which configuration was saved from is dead, all this function does is restore the three variables
window-min-height,window-min-widthandminibuffer-scroll-window.Here is a way of using this function to get the same effect as
save-window-excursion:(let ((config (current-window-configuration))) (unwind-protect (progn (split-window-vertically nil) ...) (set-window-configuration config)))
This special form records the window configuration, executes forms in sequence, then restores the earlier window configuration. The window configuration includes the value of point and the portion of the buffer that is visible. It also includes the choice of selected window. However, it does not include the value of point in the current buffer; use
save-excursionalso, if you wish to preserve that.Don't use this construct when
save-selected-windowis all you need.Exit from
save-window-excursionalways triggers execution of thewindow-size-change-functions. (It doesn't know how to tell whether the restored configuration actually differs from the one in effect at the end of the forms.)The return value is the value of the final form in forms. For example:
(split-window) => #<window 25 on control.texi> (setq w (selected-window)) => #<window 19 on control.texi> (save-window-excursion (delete-other-windows w) (switch-to-buffer "foo") 'do-something) => do-something ;; The screen is now split again.
This function returns
tif object is a window configuration.
This function compares two window configurations as regards the structure of windows, but ignores the values of point and mark and the saved scrolling positions—it can return
teven if those aspects differ.The function
equalcan also compare two window configurations; it regards configurations as unequal if they differ in any respect, even a saved point or mark.
Primitives to look inside of window configurations would make sense, but none are implemented. It is not clear they are useful enough to be worth implementing.
This section describes how a Lisp program can take action whenever a
window displays a different part of its buffer or a different buffer.
There are three actions that can change this: scrolling the window,
switching buffers in the window, and changing the size of the window.
The first two actions run window-scroll-functions; the last runs
window-size-change-functions. The paradigmatic use of these
hooks is in the implementation of Lazy Lock mode; see Lazy Lock.
This variable holds a list of functions that Emacs should call before redisplaying a window with scrolling. It is not a normal hook, because each function is called with two arguments: the window, and its new display-start position.
Displaying a different buffer in the window also runs these functions.
These functions must be careful in using
window-end(see Window Start); if you need an up-to-date value, you must use the update argument to ensure you get it.
This variable holds a list of functions to be called if the size of any window changes for any reason. The functions are called just once per redisplay, and just once for each frame on which size changes have occurred.
Each function receives the frame as its sole argument. There is no direct way to find out which windows on that frame have changed size, or precisely how. However, if a size-change function records, at each call, the existing windows and their sizes, it can also compare the present sizes and the previous sizes.
Creating or deleting windows counts as a size change, and therefore causes these functions to be called. Changing the frame size also counts, because it changes the sizes of the existing windows.
It is not a good idea to use
save-window-excursion(see Window Configurations) in these functions, because that always counts as a size change, and it would cause these functions to be called over and over. In most cases,save-selected-window(see Selecting Windows) is what you need here.
This abnormal hook is run whenever redisplay in a window uses text that extends past a specified end trigger position. You set the end trigger position with the function
set-window-redisplay-end-trigger. The functions are called with two arguments: the window, and the end trigger position. Storingnilfor the end trigger position turns off the feature, and the trigger value is automatically reset toniljust after the hook is run.
This function sets window's end trigger position at position.
This function returns window's current end trigger position.
A normal hook that is run every time you change the window configuration of an existing frame. This includes splitting or deleting windows, changing the sizes of windows, or displaying a different buffer in a window. The frame whose window configuration has changed is the selected frame when this hook runs.
A frame is a rectangle on the screen that contains one or more Emacs windows. A frame initially contains a single main window (plus perhaps a minibuffer window), which you can subdivide vertically or horizontally into smaller windows.
When Emacs runs on a text-only terminal, it starts with one terminal frame. If you create additional ones, Emacs displays one and only one at any given time—on the terminal screen, of course.
When Emacs communicates directly with a supported window system, such as X, it does not have a terminal frame; instead, it starts with a single window frame, but you can create more, and Emacs can display several such frames at once as is usual for window systems.
This predicate returns a non-
nilvalue if object is a frame, andnilotherwise. For a frame, the value indicates which kind of display the frame uses:
x- The frame is displayed in an X window.
t- A terminal frame on a character display.
mac- The frame is displayed on a Macintosh.
w32- The frame is displayed on MS-Windows 9X/NT.
pc- The frame is displayed on an MS-DOS terminal.
See Display, for information about the related topic of controlling Emacs redisplay.
To create a new frame, call the function make-frame.
This function creates a new frame. If you are using a supported window system, it makes a window frame; otherwise, it makes a terminal frame.
The argument is an alist specifying frame parameters. Any parameters not mentioned in alist default according to the value of the variable
default-frame-alist; parameters not specified even there default from the standard X resources or whatever is used instead on your system.The set of possible parameters depends in principle on what kind of window system Emacs uses to display its frames. See Window Frame Parameters, for documentation of individual parameters you can specify.
A normal hook run by
make-framebefore it actually creates the frame.
An abnormal hook run by
make-frameafter it creates the frame. Each function inafter-make-frame-functionsreceives one argument, the frame just created.
A single Emacs can talk to more than one X display.
Initially, Emacs uses just one display—the one chosen with the
DISPLAY environment variable or with the ‘--display’ option
(see Initial Options). To connect to
another display, use the command make-frame-on-display or specify
the display frame parameter when you create the frame.
Emacs treats each X server as a separate terminal, giving each one its own selected frame and its own minibuffer windows. However, only one of those frames is “the selected frame” at any given moment, see Input Focus.
A few Lisp variables are terminal-local; that is, they have a
separate binding for each terminal. The binding in effect at any time
is the one for the terminal that the currently selected frame belongs
to. These variables include default-minibuffer-frame,
defining-kbd-macro, last-kbd-macro, and
system-key-alist. They are always terminal-local, and can never
be buffer-local (see Buffer-Local Variables) or frame-local.
A single X server can handle more than one screen. A display name ‘host:server.screen’ has three parts; the last part specifies the screen number for a given server. When you use two screens belonging to one server, Emacs knows by the similarity in their names that they share a single keyboard, and it treats them as a single terminal.
This creates a new frame on display display, taking the other frame parameters from parameters. Aside from the display argument, it is like
make-frame(see Creating Frames).
This returns a list that indicates which X displays Emacs has a connection to. The elements of the list are strings, and each one is a display name.
This function opens a connection to the X display display. It does not create a frame on that display, but it permits you to check that communication can be established with that display.
The optional argument xrm-string, if not
nil, is a string of resource names and values, in the same format used in the .Xresources file. The values you specify override the resource values recorded in the X server itself; they apply to all Emacs frames created on this display. Here's an example of what this string might look like:"*BorderWidth: 3\n*InternalBorder: 2\n"See Resources.
If must-succeed is non-
nil, failure to open the connection terminates Emacs. Otherwise, it is an ordinary Lisp error.
This function closes the connection to display display. Before you can do this, you must first delete all the frames that were open on that display (see Deleting Frames).
A frame has many parameters that control its appearance and behavior. Just what parameters a frame has depends on what display mechanism it uses.
Frame parameters exist mostly for the sake of window systems. A
terminal frame has a few parameters, mostly for compatibility's sake;
only the height, width, name, title,
menu-bar-lines, buffer-list and buffer-predicate
parameters do something special. If the terminal supports colors, the
parameters foreground-color, background-color,
background-mode and display-type are also meaningful.
These functions let you read and change the parameter values of a frame.
This function returns the value of the parameter named parameter of frame. If frame is
nil, it returns the selected frame's parameter.
The function
frame-parametersreturns an alist listing all the parameters of frame and their values.
This function alters the parameters of frame frame based on the elements of alist. Each element of alist has the form
(parm.value), where parm is a symbol naming a parameter. If you don't mention a parameter in alist, its value doesn't change.
You can specify the parameters for the initial startup frame
by setting initial-frame-alist in your init file (see Init File).
This variable's value is an alist of parameter values used when creating the initial window frame. You can set this variable to specify the appearance of the initial frame without altering subsequent frames. Each element has the form:
(parameter . value)Emacs creates the initial frame before it reads your init file. After reading that file, Emacs checks
initial-frame-alist, and applies the parameter settings in the altered value to the already created initial frame.If these settings affect the frame geometry and appearance, you'll see the frame appear with the wrong ones and then change to the specified ones. If that bothers you, you can specify the same geometry and appearance with X resources; those do take effect before the frame is created. See X Resources.
X resource settings typically apply to all frames. If you want to specify some X resources solely for the sake of the initial frame, and you don't want them to apply to subsequent frames, here's how to achieve this. Specify parameters in
default-frame-alistto override the X resources for subsequent frames; then, to prevent these from affecting the initial frame, specify the same parameters ininitial-frame-alistwith values that match the X resources.
If these parameters specify a separate minibuffer-only frame with
(minibuffer . nil), and you have not created one, Emacs creates
one for you.
This variable's value is an alist of parameter values used when creating an initial minibuffer-only frame—if such a frame is needed, according to the parameters for the main initial frame.
This is an alist specifying default values of frame parameters for all Emacs frames—the first frame, and subsequent frames. When using the X Window System, you can get the same results by means of X resources in many cases.
See also special-display-frame-alist, in Choosing Window.
If you use options that specify window appearance when you invoke Emacs,
they take effect by adding elements to default-frame-alist. One
exception is ‘-geometry’, which adds the specified position to
initial-frame-alist instead. See Command Arguments.
Just what parameters a frame has depends on what display mechanism it
uses. Here is a table of the parameters that have special meanings in a
window frame; of these, name, title, height,
width, buffer-list and buffer-predicate provide
meaningful information in terminal frames.
display"host:dpy.screen", just like the
DISPLAY environment variable.
titlenil title, it appears in the window system's
border for the frame, and also in the mode line of windows in that frame
if mode-line-frame-identification uses ‘%F’
(see %-Constructs). This is normally the case when Emacs is not
using a window system, and can only display one frame at a time.
See Frame Titles.
nametitle parameter is unspecified or nil. If
you don't specify a name, Emacs sets the frame name automatically
(see Frame Titles).
If you specify the frame name explicitly when you create the frame, the
name is also used (instead of the name of the Emacs executable) when
looking up X resources for the frame.
left(+ pos) which permits specifying a
negative pos value.
A negative number −pos, or a list of the form (-
pos), actually specifies the position of the right edge of the
window with respect to the right edge of the screen. A positive value
of pos counts toward the left. Reminder: if the
parameter is a negative integer −pos, then pos is
positive.
Some window managers ignore program-specified positions. If you want to
be sure the position you specify is not ignored, specify a
non-nil value for the user-position parameter as well.
top(+ pos) which permits specifying a
negative pos value.
A negative number −pos, or a list of the form (-
pos), actually specifies the position of the bottom edge of the
window with respect to the bottom edge of the screen. A positive value
of pos counts toward the top. Reminder: if the
parameter is a negative integer −pos, then pos is
positive.
Some window managers ignore program-specified positions. If you want to
be sure the position you specify is not ignored, specify a
non-nil value for the user-position parameter as well.
icon-lefticon-topuser-positionleft and top parameters, use this parameter to say whether
the specified position was user-specified (explicitly requested in some
way by a human user) or merely program-specified (chosen by a program).
A non-nil value says the position was user-specified.
Window managers generally heed user-specified positions, and some heed
program-specified positions too. But many ignore program-specified
positions, placing the window in a default fashion or letting the user
place it with the mouse. Some window managers, including twm,
let the user specify whether to obey program-specified positions or
ignore them.
When you call make-frame, you should specify a non-nil
value for this parameter if the values of the left and top
parameters represent the user's stated preference; otherwise, use
nil.
heightframe-pixel-height; see Size and Position.)
widthframe-pixel-width; see Size and Position.)
window-idouter-window-idminibuffert means
yes, nil means no, only means this frame is just a
minibuffer. If the value is a minibuffer window (in some other frame),
the new frame uses that minibuffer.
buffer-predicateother-buffer uses this predicate (from the selected frame) to
decide which buffers it should consider, if the predicate is not
nil. It calls the predicate with one argument, a buffer, once for
each buffer; if the predicate returns a non-nil value, it
considers that buffer.
buffer-listfontauto-raisenil means yes).
auto-lowernil means yes).
vertical-scroll-barsleft,
right, and nil for no scroll bars.
horizontal-scroll-barsnil means yes). (Horizontal scroll bars are not currently
implemented.)
scroll-bar-widthicon-typenil value specifies the default bitmap icon (a
picture of a gnu); nil specifies a text icon.
icon-namenil, the frame's title is used.
foreground-colordefault on the frame in question.
background-colordefault on the frame in question.
background-modedark or light, according
to whether the background color is a light one or a dark one.
mouse-colormouse.
cursor-colorcursor.
border-colorborder.
scroll-bar-foregroundnil, the color for the foreground of scroll bars.
Changing this parameter is equivalent to setting the foreground color of
face scroll-bar.
scroll-bar-backgroundnil, the color for the background of scroll bars.
Changing this parameter is equivalent to setting the foreground color of
face scroll-bar.
display-typecolor, grayscale or
mono.
cursor-typebar,
box, and (bar . width). The symbol box
specifies an ordinary black box overlaying the character after point;
that is the default. The symbol bar specifies a vertical bar
between characters as the cursor. (bar . width) specifies
a bar width pixels wide.
The buffer-local variable cursor-type overrides the value of
the cursor-type frame parameter, and can in addition have
values t (use the cursor specified for the frame) and
nil (don't display a cursor).
border-widthinternal-border-widthunsplittablenil, this frame's window is never split automatically.
visibilitynil for invisible, t for visible, and icon for
iconified. See Visibility of Frames.
menu-bar-linesscreen-gammatool-bar-linesnil means
don't display a tool bar.
line-spacing
You can read or change the size and position of a frame using the
frame parameters left, top, height, and
width. Whatever geometry parameters you don't specify are chosen
by the window manager in its usual fashion.
Here are some special features for working with sizes and positions. (For the precise meaning of “selected frame” used by these functions, see Input Focus.)
This function sets the position of the top left corner of frame to left and top. These arguments are measured in pixels, and normally count from the top left corner of the screen.
Negative parameter values position the bottom edge of the window up from the bottom edge of the screen, or the right window edge to the left of the right edge of the screen. It would probably be better if the values were always counted from the left and top, so that negative arguments would position the frame partly off the top or left edge of the screen, but it seems inadvisable to change that now.
These functions return the height and width of frame, measured in lines and columns. If you don't supply frame, they use the selected frame.
These functions are old aliases for
frame-heightandframe-width. When you are using a non-window terminal, the size of the frame is normally the same as the size of the terminal screen.
These functions return the height and width of frame, measured in pixels. If you don't supply frame, they use the selected frame.
These functions return the height and width of a character in frame, measured in pixels. The values depend on the choice of font. If you don't supply frame, these functions use the selected frame.
This function sets the size of frame, measured in characters; cols and rows specify the new width and height.
To set the size based on values measured in pixels, use
frame-char-heightandframe-char-widthto convert them to units of characters.
This function resizes frame to a height of lines lines. The sizes of existing windows in frame are altered proportionally to fit.
If pretend is non-
nil, then Emacs displays lines lines of output in frame, but does not change its value for the actual height of the frame. This is only useful for a terminal frame. Using a smaller height than the terminal actually implements may be useful to reproduce behavior observed on a smaller screen, or if the terminal malfunctions when using its whole screen. Setting the frame height “for real” does not always work, because knowing the correct actual size may be necessary for correct cursor positioning on a terminal frame.
This function sets the width of frame, measured in characters. The argument pretend has the same meaning as in
set-frame-height.
The older functions set-screen-height and
set-screen-width were used to specify the height and width of the
screen, in Emacs versions that did not support multiple frames. They
are semi-obsolete, but still work; they apply to the selected frame.
The function
x-parse-geometryconverts a standard X window geometry string to an alist that you can use as part of the argument tomake-frame.The alist describes which parameters were specified in geom, and gives the values specified for them. Each element looks like
(parameter.value). The possible parameter values areleft,top,width, andheight.For the size parameters, the value must be an integer. The position parameter names
leftandtopare not totally accurate, because some values indicate the position of the right or bottom edges instead. These are the value possibilities for the position parameters:
- an integer
- A positive integer relates the left edge or top edge of the window to the left or top edge of the screen. A negative integer relates the right or bottom edge of the window to the right or bottom edge of the screen.
(+position)- This specifies the position of the left or top edge of the window relative to the left or top edge of the screen. The integer position may be positive or negative; a negative value specifies a position outside the screen.
(-position)- This specifies the position of the right or bottom edge of the window relative to the right or bottom edge of the screen. The integer position may be positive or negative; a negative value specifies a position outside the screen.
Here is an example:
(x-parse-geometry "35x70+0-0") => ((height . 70) (width . 35) (top - 0) (left . 0))
Every frame has a name parameter; this serves as the default
for the frame title which window systems typically display at the top of
the frame. You can specify a name explicitly by setting the name
frame property.
Normally you don't specify the name explicitly, and Emacs computes the
frame name automatically based on a template stored in the variable
frame-title-format. Emacs recomputes the name each time the
frame is redisplayed.
This variable specifies how to compute a name for a frame when you have not explicitly specified one. The variable's value is actually a mode line construct, just like
mode-line-format. See Mode Line Data.
This variable specifies how to compute the name for an iconified frame, when you have not explicitly specified the frame title. This title appears in the icon itself.
This variable is set automatically by Emacs. Its value is
twhen there are two or more frames (not counting minibuffer-only frames or invisible frames). The default value offrame-title-formatusesmultiple-framesso as to put the buffer name in the frame title only when there is more than one frame.
Frames remain potentially visible until you explicitly delete them. A deleted frame cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a frame aside from restoring a saved frame configuration (see Frame Configurations); this is similar to the way windows behave.
This function deletes the frame frame after running the hook
delete-frame-hook. By default, frame is the selected frame.A frame cannot be deleted if its minibuffer is used by other frames. Normally, you cannot delete a frame if all other frames are invisible, but if the force is non-
nil, then you are allowed to do so.
The function
frame-live-preturns non-nilif the frame frame has not been deleted.
Some window managers provide a command to delete a window. These work
by sending a special message to the program that operates the window.
When Emacs gets one of these commands, it generates a
delete-frame event, whose normal definition is a command that
calls the function delete-frame. See Misc Events.
The function
frame-listreturns a list of all the frames that have not been deleted. It is analogous tobuffer-listfor buffers, and includes frames on all terminals. The list that you get is newly created, so modifying the list doesn't have any effect on the internals of Emacs.
This function returns a list of just the currently visible frames. See Visibility of Frames. (Terminal frames always count as “visible”, even though only the selected one is actually displayed.)
The function
next-framelets you cycle conveniently through all the frames on the current display from an arbitrary starting point. It returns the “next” frame after frame in the cycle. If frame is omitted ornil, it defaults to the selected frame (see Input Focus).The second argument, minibuf, says which frames to consider:
nil- Exclude minibuffer-only frames.
visible- Consider all visible frames.
- 0
- Consider all visible or iconified frames.
- a window
- Consider only the frames using that particular window as their minibuffer.
- anything else
- Consider all frames.
Like
next-frame, but cycles through all frames in the opposite direction.
See also next-window and previous-window, in Cyclic Window Ordering.
Each window is part of one and only one frame; you can get the frame
with window-frame.
All the non-minibuffer windows in a frame are arranged in a cyclic order. The order runs from the frame's top window, which is at the upper left corner, down and to the right, until it reaches the window at the lower right corner (always the minibuffer window, if the frame has one), and then it moves back to the top. See Cyclic Window Ordering.
At any time, exactly one window on any frame is selected within the
frame. The significance of this designation is that selecting the
frame also selects this window. You can get the frame's current
selected window with frame-selected-window.
This function returns the window on frame that is selected within frame.
Conversely, selecting a window for Emacs with select-window also
makes that window selected within its frame. See Selecting Windows.
Another function that (usually) returns one of the windows in a given
frame is minibuffer-window. See Minibuffer Misc.
Normally, each frame has its own minibuffer window at the bottom, which
is used whenever that frame is selected. If the frame has a minibuffer,
you can get it with minibuffer-window (see Minibuffer Misc).
However, you can also create a frame with no minibuffer. Such a frame
must use the minibuffer window of some other frame. When you create the
frame, you can specify explicitly the minibuffer window to use (in some
other frame). If you don't, then the minibuffer is found in the frame
which is the value of the variable default-minibuffer-frame. Its
value should be a frame that does have a minibuffer.
If you use a minibuffer-only frame, you might want that frame to raise
when you enter the minibuffer. If so, set the variable
minibuffer-auto-raise to t. See Raising and Lowering.
This variable specifies the frame to use for the minibuffer window, by default. It is always local to the current terminal and cannot be buffer-local. See Multiple Displays.
At any time, one frame in Emacs is the selected frame. The selected window always resides on the selected frame.
When Emacs displays its frames on several terminals (see Multiple Displays), each terminal has its own selected frame. But only one of these is “the selected frame”: it's the frame that belongs to the terminal from which the most recent input came. That is, when Emacs runs a command that came from a certain terminal, the selected frame is the one of that terminal. Since Emacs runs only a single command at any given time, it needs to consider only one selected frame at a time; this frame is what we call the selected frame in this manual. The display on which the selected frame is displayed is the selected frame's display.
Some window systems and window managers direct keyboard input to the window object that the mouse is in; others require explicit clicks or commands to shift the focus to various window objects. Either way, Emacs automatically keeps track of which frame has the focus.
Lisp programs can also switch frames “temporarily” by calling the
function select-frame. This does not alter the window system's
concept of focus; rather, it escapes from the window manager's control
until that control is somehow reasserted.
When using a text-only terminal, only the selected terminal frame is
actually displayed on the terminal. switch-frame is the only way
to switch frames, and the change lasts until overridden by a subsequent
call to switch-frame. Each terminal screen except for the
initial one has a number, and the number of the selected frame appears
in the mode line before the buffer name (see Mode Line Variables).
This function selects frame frame, temporarily disregarding the focus of the X server if any. The selection of frame lasts until the next time the user does something to select a different frame, or until the next time this function is called. The specified frame becomes the selected frame, as explained above, and the terminal that frame is on becomes the selected terminal.
In general, you should never use
select-framein a way that could switch to a different terminal without switching back when you're done.
Emacs cooperates with the window system by arranging to select frames as
the server and window manager request. It does so by generating a
special kind of input event, called a focus event, when
appropriate. The command loop handles a focus event by calling
handle-switch-frame. See Focus Events.
This function handles a focus event by selecting frame frame.
Focus events normally do their job by invoking this command. Don't call it for any other reason.
This function redirects focus from frame to focus-frame. This means that focus-frame will receive subsequent keystrokes and events intended for frame. After such an event, the value of
last-event-framewill be focus-frame. Also, switch-frame events specifying frame will instead select focus-frame.If focus-frame is
nil, that cancels any existing redirection for frame, which therefore once again receives its own events.One use of focus redirection is for frames that don't have minibuffers. These frames use minibuffers on other frames. Activating a minibuffer on another frame redirects focus to that frame. This puts the focus on the minibuffer's frame, where it belongs, even though the mouse remains in the frame that activated the minibuffer.
Selecting a frame can also change focus redirections. Selecting frame
bar, whenfoohad been selected, changes any redirections pointing tofooso that they point tobarinstead. This allows focus redirection to work properly when the user switches from one frame to another usingselect-window.This means that a frame whose focus is redirected to itself is treated differently from a frame whose focus is not redirected.
select-frameaffects the former but not the latter.The redirection lasts until
redirect-frame-focusis called to change it.
This option is how you inform Emacs whether the window manager transfers focus when the user moves the mouse. Non-
nilsays that it does. When this is so, the commandother-framemoves the mouse to a position consistent with the new selected frame.
A window frame may be visible, invisible, or iconified. If it is visible, you can see its contents. If it is iconified, the frame's contents do not appear on the screen, but an icon does. If the frame is invisible, it doesn't show on the screen, not even as an icon.
Visibility is meaningless for terminal frames, since only the selected one is actually displayed in any case.
This function makes frame frame visible. If you omit frame, it makes the selected frame visible.
This function makes frame frame invisible. If you omit frame, it makes the selected frame invisible.
This function iconifies frame frame. If you omit frame, it iconifies the selected frame.
This returns the visibility status of frame frame. The value is
tif frame is visible,nilif it is invisible, andiconif it is iconified.
The visibility status of a frame is also available as a frame parameter. You can read or change it as such. See Window Frame Parameters.
The user can iconify and deiconify frames with the window manager. This happens below the level at which Emacs can exert any control, but Emacs does provide events that you can use to keep track of such changes. See Misc Events.
Most window systems use a desktop metaphor. Part of this metaphor is the idea that windows are stacked in a notional third dimension perpendicular to the screen surface, and thus ordered from “highest” to “lowest”. Where two windows overlap, the one higher up covers the one underneath. Even a window at the bottom of the stack can be seen if no other window overlaps it.
A window's place in this ordering is not fixed; in fact, users tend to change the order frequently. Raising a window means moving it “up”, to the top of the stack. Lowering a window means moving it to the bottom of the stack. This motion is in the notional third dimension only, and does not change the position of the window on the screen.
You can raise and lower Emacs frame Windows with these functions:
This function raises frame frame (default, the selected frame).
This function lowers frame frame (default, the selected frame).
If this is non-
nil, activation of the minibuffer raises the frame that the minibuffer window is in.
You can also enable auto-raise (raising automatically when a frame is selected) or auto-lower (lowering automatically when it is deselected) for any frame using frame parameters. See Window Frame Parameters.
A frame configuration records the current arrangement of frames, all their properties, and the window configuration of each one. (See Window Configurations.)
This function returns a frame configuration list that describes the current arrangement of frames and their contents.
This function restores the state of frames described in configuration.
Ordinarily, this function deletes all existing frames not listed in configuration. But if nodelete is non-
nil, the unwanted frames are iconified instead.
Sometimes it is useful to track the mouse, which means to display something to indicate where the mouse is and move the indicator as the mouse moves. For efficient mouse tracking, you need a way to wait until the mouse actually moves.
The convenient way to track the mouse is to ask for events to represent mouse motion. Then you can wait for motion by waiting for an event. In addition, you can easily handle any other sorts of events that may occur. That is useful, because normally you don't want to track the mouse forever—only until some other event, such as the release of a button.
This special form executes body, with generation of mouse motion events enabled. Typically body would use
read-eventto read the motion events and modify the display accordingly. See Motion Events, for the format of mouse motion events.The value of
track-mouseis that of the last form in body. You should design body to return when it sees the up-event that indicates the release of the button, or whatever kind of event means it is time to stop tracking.
The usual purpose of tracking mouse motion is to indicate on the screen the consequences of pushing or releasing a button at the current position.
In many cases, you can avoid the need to track the mouse by using
the mouse-face text property (see Special Properties).
That works at a much lower level and runs more smoothly than
Lisp-level mouse tracking.
The functions mouse-position and set-mouse-position
give access to the current position of the mouse.
This function returns a description of the position of the mouse. The value looks like
(frame x.y), where x and y are integers giving the position in characters relative to the top left corner of the inside of frame.
If non-
nil, the value of this variable is a function formouse-positionto call.mouse-positioncalls this function just before returning, with its normal return value as the sole argument, and it returns whatever this function returns to it.This abnormal hook exists for the benefit of packages like xt-mouse.el that need to do mouse handling at the Lisp level.
This function warps the mouse to position x, y in frame frame. The arguments x and y are integers, giving the position in characters relative to the top left corner of the inside of frame. If frame is not visible, this function does nothing. The return value is not significant.
This function is like
mouse-positionexcept that it returns coordinates in units of pixels rather than units of characters.
This function warps the mouse like
set-mouse-positionexcept that x and y are in units of pixels rather than units of characters. These coordinates are not required to be within the frame.If frame is not visible, this function does nothing. The return value is not significant.
When using a window system, a Lisp program can pop up a menu so that the user can choose an alternative with the mouse.
This function displays a pop-up menu and returns an indication of what selection the user makes.
The argument position specifies where on the screen to put the menu. It can be either a mouse button event (which says to put the menu where the user actuated the button) or a list of this form:
((xoffset yoffset) window)where xoffset and yoffset are coordinates, measured in pixels, counting from the top left corner of window's frame.
If position is
t, it means to use the current mouse position. If position isnil, it means to precompute the key binding equivalents for the keymaps specified in menu, without actually displaying or popping up the menu.The argument menu says what to display in the menu. It can be a keymap or a list of keymaps (see Menu Keymaps). Alternatively, it can have the following form:
(title pane1 pane2...)where each pane is a list of form
(title (line . item)...)Each line should be a string, and each item should be the value to return if that line is chosen.
Usage note: Don't use x-popup-menu to display a menu
if you could do the job with a prefix key defined with a menu keymap.
If you use a menu keymap to implement a menu, C-h c and C-h
a can see the individual items in that menu and provide help for them.
If instead you implement the menu by defining a command that calls
x-popup-menu, the help facilities cannot know what happens inside
that command, so they cannot give any help for the menu's items.
The menu bar mechanism, which lets you switch between submenus by
moving the mouse, cannot look within the definition of a command to see
that it calls x-popup-menu. Therefore, if you try to implement a
submenu using x-popup-menu, it cannot work with the menu bar in
an integrated fashion. This is why all menu bar submenus are
implemented with menu keymaps within the parent menu, and never with
x-popup-menu. See Menu Bar,
If you want a menu bar submenu to have contents that vary, you should
still use a menu keymap to implement it. To make the contents vary, add
a hook function to menu-bar-update-hook to update the contents of
the menu keymap as necessary.
A dialog box is a variant of a pop-up menu—it looks a little
different, it always appears in the center of a frame, and it has just
one level and one pane. The main use of dialog boxes is for asking
questions that the user can answer with “yes”, “no”, and a few other
alternatives. The functions y-or-n-p and yes-or-no-p use
dialog boxes instead of the keyboard, when called from commands invoked
by mouse clicks.
This function displays a pop-up dialog box and returns an indication of what selection the user makes. The argument contents specifies the alternatives to offer; it has this format:
(title (string . value)...)which looks like the list that specifies a single pane for
x-popup-menu.The return value is value from the chosen alternative.
An element of the list may be just a string instead of a cons cell
(string.value). That makes a box that cannot be selected.If
nilappears in the list, it separates the left-hand items from the right-hand items; items that precede thenilappear on the left, and items that follow thenilappear on the right. If you don't include anilin the list, then approximately half the items appear on each side.Dialog boxes always appear in the center of a frame; the argument position specifies which frame. The possible values are as in
x-popup-menu, but the precise coordinates don't matter; only the frame matters.In some configurations, Emacs cannot display a real dialog box; so instead it displays the same items in a pop-up menu in the center of the frame.
These variables specify which shape to use for the mouse pointer in various situations, when using the X Window System:
x-pointer-shapex-sensitive-text-pointer-shapeThese variables affect newly created frames. They do not normally affect existing frames; however, if you set the mouse color of a frame, that also updates its pointer shapes based on the current values of these variables. See Window Frame Parameters.
The values you can use, to specify either of these pointer shapes, are defined in the file lisp/term/x-win.el. Use M-x apropos <RET> x-pointer <RET> to see a list of them.
The X server records a set of selections which permit transfer of data between application programs. The various selections are distinguished by selection types, represented in Emacs by symbols. X clients including Emacs can read or set the selection for any given type.
This function sets a “selection” in the X server. It takes two arguments: a selection type type, and the value to assign to it, data. If data is
nil, it means to clear out the selection. Otherwise, data may be a string, a symbol, an integer (or a cons of two integers or list of two integers), an overlay, or a cons of two markers pointing to the same buffer. An overlay or a pair of markers stands for text in the overlay or between the markers.The argument data may also be a vector of valid non-vector selection values.
Each possible type has its own selection value, which changes independently. The usual values of type are
PRIMARYandSECONDARY; these are symbols with upper-case names, in accord with X Window System conventions. The default isPRIMARY.
This function accesses selections set up by Emacs or by other X clients. It takes two optional arguments, type and data-type. The default for type, the selection type, is
PRIMARY.The data-type argument specifies the form of data conversion to use, to convert the raw data obtained from another X client into Lisp data. Meaningful values include
TEXT,STRING,TARGETS,LENGTH,DELETE,FILE_NAME,CHARACTER_POSITION,LINE_NUMBER,COLUMN_NUMBER,OWNER_OS,HOST_NAME,USER,CLASS,NAME,ATOM, andINTEGER. (These are symbols with upper-case names in accord with X conventions.) The default for data-type isSTRING.
The X server also has a set of numbered cut buffers which can store text or other data being moved between applications. Cut buffers are considered obsolete, but Emacs supports them for the sake of X clients that still use them.
This function stores string into the first cut buffer (cut buffer 0). If push is
nil, only the first cut buffer is changed. If push is non-nil, that says to move the values down through the series of cut buffers, much like the way successive kills in Emacs move down the kill ring. In other words, the previous value of the first cut buffer moves into the second cut buffer, and the second to the third, and so on through all eight cut buffers.
This variable specifies the coding system to use when reading and writing selections, the clipboard, or a cut buffer. See Coding Systems. The default is
compound-text, which converts to the text representation that X11 normally uses.
When Emacs runs on MS-Windows, it does not implement X selections in
general, but it does support the clipboard. x-get-selection
and x-set-selection on MS-Windows support the text data type
only; if the clipboard holds other types of data, Emacs treats the
clipboard as empty.
If this is non-
nil, the Emacs yank functions consult the clipboard before the primary selection, and the kill functions store in the clipboard as well as the primary selection. Otherwise they do not access the clipboard at all. The default isnilon most systems, button MS-Windows.
These functions provide a way to determine which color names are valid, and what they look like. In some cases, the value depends on the selected frame, as described below; see Input Focus, for the meaning of the term “selected frame”.
This function reports whether a color name is meaningful. It returns
tif so; otherwise,nil. The argument frame says which frame's display to ask about; if frame is omitted ornil, the selected frame is used.Note that this does not tell you whether the display you are using really supports that color. When using X, you can ask for any defined color on any kind of display, and you will get some result—typically, the closest it can do. To determine whether a frame can really display a certain color, use
color-supported-p(see below).This function used to be called
x-color-defined-p, and that name is still supported as an alias.
This function returns a list of the color names that are defined and supported on frame frame (default, the selected frame).
This function used to be called
x-defined-colors, and that name is still supported as an alias.
This returns
tif frame can really display the color color (or at least something close to it). If frame is omitted ornil, the question applies to the selected frame.Some terminals support a different set of colors for foreground and background. If background-p is non-
nil, that means you are asking whether color can be used as a background; otherwise you are asking whether it can be used as a foreground.The argument color must be a valid color name.
This returns
tif color is a shade of gray, as defined on frame's display. If frame is omitted ornil, the question applies to the selected frame. The argument color must be a valid color name.
This function returns a value that describes what color should ideally look like. If color is defined, the value is a list of three integers, which give the amount of red, the amount of green, and the amount of blue. Each integer ranges in principle from 0 to 65535, but in practice no value seems to be above 65280. This kind of three-element list is called an rgb value.
If color is not defined, the value is
nil.(color-values "black") => (0 0 0) (color-values "white") => (65280 65280 65280) (color-values "red") => (65280 0 0) (color-values "pink") => (65280 49152 51968) (color-values "hungry") => nilThe color values are returned for frame's display. If frame is omitted or
nil, the information is returned for the selected frame's display.This function used to be called
x-color-values, and that name is still supported as an alias.
Emacs can display color on text-only terminals, starting with version 21. These terminals support only a small number of colors, and the computer uses small integers to select colors on the terminal. This means that the computer cannot reliably tell what the selected color looks like; instead, you have to inform your application which small integers correspond to which colors. However, Emacs does know the standard set of colors and will try to use them automatically.
Several of these functions use or return rgb values. An rgb value is a list of three integers, which give the amount of red, the amount of green, and the amount of blue. Each integer ranges in principle from 0 to 65535, but in practice the largest value used is 65280.
These functions accept a display (either a frame or the name of a terminal) as an optional argument. We hope in the future to make Emacs support more than one text-only terminal at one time; then this argument will specify which terminal to operate on (the default being the selected frame's terminal; see Input Focus). At present, though, the display argument has no effect.
This function associates the color name name with color number number on the terminal.
The optional argument rgb, if specified, is an rgb value; it says what the color actually looks like. If you do not specify rgb, then this color cannot be used by
tty-color-approximateto approximate other colors, because Emacs does not know what it looks like.
This function clears the table of defined colors for a text-only terminal.
This function returns an alist recording the known colors supported by a text-only terminal.
Each element has the form
(name number.rgb)or(name number). Here, name is the color name, number is the number used to specify it to the terminal. If present, rgb is an rgb value that says what the color actually looks like.
This function finds the closest color, among the known colors supported for display, to that described by the rgb value rgb.
This function finds the closest color to color among the known colors supported for display. If the name color is not defined, the value is
nil.color can be an X-style
"#xxxyyyzzz"specification instead of an actual name. The format"RGB:xx/yy/zz"is also supported.
The function
x-get-resourceretrieves a resource value from the X Windows defaults database.Resources are indexed by a combination of a key and a class. This function searches using a key of the form ‘instance.attribute’ (where instance is the name under which Emacs was invoked), and using ‘Emacs.class’ as the class.
The optional arguments component and subclass add to the key and the class, respectively. You must specify both of them or neither. If you specify them, the key is ‘instance.component.attribute’, and the class is ‘Emacs.class.subclass’.
This variable specifies the application name that
x-get-resourceshould look up. The default value is"Emacs". You can examine X resources for application names other than “Emacs” by binding this variable to some other string, around a call tox-get-resource.
See X Resources.
The functions in this section describe the basic capabilities of a particular display. Lisp programs can use them to adapt their behavior to what the display can do. For example, a program that ordinarly uses a popup menu could use the minibuffer if popup menus are not supported.
The optional argument display in these functions specifies which
display to ask the question about. It can be a display name, a frame
(which designates the display that frame is on), or nil (which
refers to the selected frame's display, see Input Focus).
See Color Names, Text Terminal Colors, for other functions to obtain information about displays.
This function returns
tif popup menus are supported on display,nilif not. Support for popup menus requires that the mouse be available, since the user cannot choose menu items without a mouse.
This function returns
tif display is a graphic display capable of displaying several frames and several different fonts at once. This is true for displays that use a window system such as X, and false for text-only terminals.
This function returns
tif display has a mouse available,nilif not.
This function returns
tif the screen is a color screen. It used to be calledx-display-color-p, and that name is still supported as an alias.
This function returns
tif the screen can display shades of gray. (All color displays can do this.)
This function returns
tif display supports selections. Windowed displays normally support selections, but they may also be supported in some other cases.
This function returns
tif display can display images. Windowed displays ought in principle to handle images, but some systems lack the support for that. On a display that does not support images, Emacs cannot display a tool bar.
This function returns the number of screens associated with the display.
This function returns the height of the screen in millimeters, or
nilif Emacs cannot get that information.
This function returns the width of the screen in millimeters, or
nilif Emacs cannot get that information.
This function returns the backing store capability of the display. Backing store means recording the pixels of windows (and parts of windows) that are not exposed, so that when exposed they can be displayed very quickly.
Values can be the symbols
always,when-mapped, ornot-useful. The function can also returnnilwhen the question is inapplicable to a certain kind of display.
This function returns non-
nilif the display supports the SaveUnder feature. That feature is used by pop-up windows to save the pixels they obscure, so that they can pop down quickly.
This function returns the number of planes the display supports. This is typically the number of bits per pixel. For a tty display, it is log to base two of the number of colours supported.
This function returns the visual class for the screen. The value is one of the symbols
static-gray,gray-scale,static-color,pseudo-color,true-color, anddirect-color.
This function returns the number of color cells the screen supports.
These functions obtain additional information specifically about X displays.
This function returns the list of version numbers of the X server running the display.
This function returns the vendor that provided the X server software.
A position is the index of a character in the text of a buffer. More precisely, a position identifies the place between two characters (or before the first character, or after the last character), so we can speak of the character before or after a given position. However, we often speak of the character “at” a position, meaning the character after that position.
Positions are usually represented as integers starting from 1, but can also be represented as markers—special objects that relocate automatically when text is inserted or deleted so they stay with the surrounding characters. See Markers.
See also the “field” feature (see Fields), which provides functions that are used by many cursur-motion commands.
Point is a special buffer position used by many editing commands, including the self-inserting typed characters and text insertion functions. Other commands move point through the text to allow editing and insertion at different places.
Like other positions, point designates a place between two characters (or before the first character, or after the last character), rather than a particular character. Usually terminals display the cursor over the character that immediately follows point; point is actually before the character on which the cursor sits.
The value of point is a number no less than 1, and no greater than the buffer size plus 1. If narrowing is in effect (see Narrowing), then point is constrained to fall within the accessible portion of the buffer (possibly at one end of it).
Each buffer has its own value of point, which is independent of the value of point in other buffers. Each window also has a value of point, which is independent of the value of point in other windows on the same buffer. This is why point can have different values in various windows that display the same buffer. When a buffer appears in only one window, the buffer's point and the window's point normally have the same value, so the distinction is rarely important. See Window Point, for more details.
This function returns the value of point in the current buffer, as an integer.
(point) => 175
This function returns the minimum accessible value of point in the current buffer. This is normally 1, but if narrowing is in effect, it is the position of the start of the region that you narrowed to. (See Narrowing.)
This function returns the maximum accessible value of point in the current buffer. This is
(1+ (buffer-size)), unless narrowing is in effect, in which case it is the position of the end of the region that you narrowed to. (See Narrowing.)
This function returns
(point-min)if flag is less than 1,(point-max)otherwise. The argument flag must be a number.
This function returns the total number of characters in the current buffer. In the absence of any narrowing (see Narrowing),
point-maxreturns a value one larger than this.If you specify a buffer, buffer, then the value is the size of buffer.
(buffer-size) => 35 (point-max) => 36
Motion functions change the value of point, either relative to the current value of point, relative to the beginning or end of the buffer, or relative to the edges of the selected window. See Point.
These functions move point based on a count of characters.
goto-char is the fundamental primitive; the other functions use
that.
This function sets point in the current buffer to the value position. If position is less than 1, it moves point to the beginning of the buffer. If position is greater than the length of the buffer, it moves point to the end.
If narrowing is in effect, position still counts from the beginning of the buffer, but point cannot go outside the accessible portion. If position is out of range,
goto-charmoves point to the beginning or the end of the accessible portion.When this function is called interactively, position is the numeric prefix argument, if provided; otherwise it is read from the minibuffer.
goto-charreturns position.
This function moves point count characters forward, towards the end of the buffer (or backward, towards the beginning of the buffer, if count is negative). If the function attempts to move point past the beginning or end of the buffer (or the limits of the accessible portion, when narrowing is in effect), an error is signaled with error code
beginning-of-bufferorend-of-buffer.In an interactive call, count is the numeric prefix argument.
This function moves point count characters backward, towards the beginning of the buffer (or forward, towards the end of the buffer, if count is negative). If the function attempts to move point past the beginning or end of the buffer (or the limits of the accessible portion, when narrowing is in effect), an error is signaled with error code
beginning-of-bufferorend-of-buffer.In an interactive call, count is the numeric prefix argument.
These functions for parsing words use the syntax table to decide whether a given character is part of a word. See Syntax Tables.
This function moves point forward count words (or backward if count is negative). “Moving one word” means moving until point crosses a word-constituent character and then encounters a word-separator character. However, this function cannot move point past the boundary of the accessible portion of the buffer, or across a field boundary (see Fields). The most common case of a field boundary is the end of the prompt in the minibuffer.
If it is possible to move count words, without being stopped prematurely by the buffer boundary or a field boundary, the value is
t. Otherwise, the return value isniland point stops at the buffer boundary or field boundary.If
inhibit-field-text-motionis non-nil, this function ignores field boundaries.In an interactive call, count is specified by the numeric prefix argument.
This function is just like
forward-word, except that it moves backward until encountering the front of a word, rather than forward.In an interactive call, count is set to the numeric prefix argument.
This variable affects the behavior of
forward-wordand everything that uses it. If it is non-nil, then characters in the “escape” and “character quote” syntax classes count as part of words. Otherwise, they do not.
If this variable is non-
nil, certain motion functions includingforward-word,forward-sentence, andforward-paragraphignore field boundaries.
To move point to the beginning of the buffer, write:
(goto-char (point-min))
Likewise, to move to the end of the buffer, use:
(goto-char (point-max))
Here are two commands that users use to do these things. They are documented here to warn you not to use them in Lisp programs, because they set the mark and display messages in the echo area.
This function moves point to the beginning of the buffer (or the limits of the accessible portion, when narrowing is in effect), setting the mark at the previous position. If n is non-
nil, then it puts point n tenths of the way from the beginning of the accessible portion of the buffer.In an interactive call, n is the numeric prefix argument, if provided; otherwise n defaults to
nil.Warning: Don't use this function in Lisp programs!
This function moves point to the end of the buffer (or the limits of the accessible portion, when narrowing is in effect), setting the mark at the previous position. If n is non-
nil, then it puts point n tenths of the way from the end of the accessible portion of the buffer.In an interactive call, n is the numeric prefix argument, if provided; otherwise n defaults to
nil.Warning: Don't use this function in Lisp programs!
Text lines are portions of the buffer delimited by newline characters, which are regarded as part of the previous line. The first text line begins at the beginning of the buffer, and the last text line ends at the end of the buffer whether or not the last character is a newline. The division of the buffer into text lines is not affected by the width of the window, by line continuation in display, or by how tabs and control characters are displayed.
This function moves point to the front of the lineth line, counting from line 1 at beginning of the buffer. If line is less than 1, it moves point to the beginning of the buffer. If line is greater than the number of lines in the buffer, it moves point to the end of the buffer—that is, the end of the last line of the buffer. This is the only case in which
goto-linedoes not necessarily move to the beginning of a line.If narrowing is in effect, then line still counts from the beginning of the buffer, but point cannot go outside the accessible portion. So
goto-linemoves point to the beginning or end of the accessible portion, if the line number specifies an inaccessible position.The return value of
goto-lineis the difference between line and the line number of the line to which point actually was able to move (in the full buffer, before taking account of narrowing). Thus, the value is positive if the scan encounters the real end of the buffer before finding the specified line. The value is zero if scan encounters the end of the accessible portion but not the real end of the buffer.In an interactive call, line is the numeric prefix argument if one has been provided. Otherwise line is read in the minibuffer.
This function moves point to the beginning of the current line. With an argument count not
nilor 1, it moves forward count−1 lines and then to the beginning of the line.This function does not move point across a field boundary (see Fields) unless doing so would move beyond there to a different line; therefore, if count is
nilor 1, and point starts at a field boundary, point does not move. To ignore field boundaries, either bindinhibit-field-text-motiontot, or use theforward-linefunction instead. For instance,(forward-line 0)does the same thing as(beginning-of-line), except that it ignores field boundaries.If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled.
Return the position that
(beginning-of-linecount)would move to.
This function moves point to the end of the current line. With an argument count not
nilor 1, it moves forward count−1 lines and then to the end of the line.This function does not move point across a field boundary (see Fields) unless doing so would move beyond there to a different line; therefore, if count is
nilor 1, and point starts at a field boundary, point does not move. To ignore field boundaries, bindinhibit-field-text-motiontot.If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled.
This function moves point forward count lines, to the beginning of the line. If count is negative, it moves point −count lines backward, to the beginning of a line. If count is zero, it moves point to the beginning of the current line.
If
forward-lineencounters the beginning or end of the buffer (or of the accessible portion) before finding that many lines, it sets point there. No error is signaled.
forward-linereturns the difference between count and the number of lines actually moved. If you attempt to move down five lines from the beginning of a buffer that has only three lines, point stops at the end of the last line, and the value will be 2.In an interactive call, count is the numeric prefix argument.
This function returns the number of lines between the positions start and end in the current buffer. If start and end are equal, then it returns 0. Otherwise it returns at least 1, even if start and end are on the same line. This is because the text between them, considered in isolation, must contain at least one line unless it is empty.
Here is an example of using
count-lines:(defun current-line () "Return the vertical position of point..." (+ (count-lines (window-start) (point)) (if (= (current-column) 0) 1 0) -1))
Also see the functions bolp and eolp in Near Point.
These functions do not move point, but test whether it is already at the
beginning or end of a line.
The line functions in the previous section count text lines, delimited only by newline characters. By contrast, these functions count screen lines, which are defined by the way the text appears on the screen. A text line is a single screen line if it is short enough to fit the width of the selected window, but otherwise it may occupy several screen lines.
In some cases, text lines are truncated on the screen rather than
continued onto additional screen lines. In these cases,
vertical-motion moves point much like forward-line.
See Truncation.
Because the width of a given string depends on the flags that control
the appearance of certain characters, vertical-motion behaves
differently, for a given piece of text, depending on the buffer it is
in, and even on the selected window (because the width, the truncation
flag, and display table may vary between windows). See Usual Display.
These functions scan text to determine where screen lines break, and thus take time proportional to the distance scanned. If you intend to use them heavily, Emacs provides caches which may improve the performance of your code. See cache-long-line-scans.
This function moves point to the start of the screen line count screen lines down from the screen line containing point. If count is negative, it moves up instead.
vertical-motionreturns the number of screen lines over which it moved point. The value may be less in absolute value than count if the beginning or end of the buffer was reached.The window window is used for obtaining parameters such as the width, the horizontal scrolling, and the display table. But
vertical-motionalways operates on the current buffer, even if window currently displays some other buffer.
This function returns the number of screen lines in the text from beg to end. The number of screen lines may be different from the number of actual lines, due to line continuation, the display table, etc. If beg and end are
nilor omitted, they default to the beginning and end of the accessible portion of the buffer.If the region ends with a newline, that is ignored unless the optional third argument count-final-newline is non-
nil.The optional fourth argument window specifies the window for obtaining parameters such as width, horizontal scrolling, and so on. The default is to use the selected window's parameters.
Like
vertical-motion,count-screen-linesalways uses the current buffer, regardless of which buffer is displayed in window. This makes possible to usecount-screen-linesin any buffer, whether or not it is currently displayed in some window.
This function moves point with respect to the text currently displayed in the selected window. It moves point to the beginning of the screen line count screen lines from the top of the window. If count is negative, that specifies a position −count lines from the bottom (or the last line of the buffer, if the buffer ends above the specified screen position).
If count is
nil, then point moves to the beginning of the line in the middle of the window. If the absolute value of count is greater than the size of the window, then point moves to the place that would appear on that screen line if the window were tall enough. This will probably cause the next redisplay to scroll to bring that location onto the screen.In an interactive call, count is the numeric prefix argument.
The value returned is the window line number point has moved to, with the top line in the window numbered 0.
This function scans the current buffer, calculating screen positions. It scans the buffer forward from position from, assuming that is at screen coordinates frompos, to position to or coordinates topos, whichever comes first. It returns the ending buffer position and screen coordinates.
The coordinate arguments frompos and topos are cons cells of the form
(hpos.vpos).The argument width is the number of columns available to display text; this affects handling of continuation lines. Use the value returned by
window-widthfor the window of your choice; normally, use(window-widthwindow).The argument offsets is either
nilor a cons cell of the form(hscroll.tab-offset). Here hscroll is the number of columns not being displayed at the left margin; most callers get this by callingwindow-hscroll. Meanwhile, tab-offset is the offset between column numbers on the screen and column numbers in the buffer. This can be nonzero in a continuation line, when the previous screen lines' widths do not add up to a multiple oftab-width. It is always zero in a non-continuation line.The window window serves only to specify which display table to use.
compute-motionalways operates on the current buffer, regardless of what buffer is displayed in window.The return value is a list of five elements:
(pos vpos hpos prevhpos contin)Here pos is the buffer position where the scan stopped, vpos is the vertical screen position, and hpos is the horizontal screen position.
The result prevhpos is the horizontal position one character back from pos. The result contin is
tif the last line was continued after (or within) the previous character.For example, to find the buffer position of column col of screen line line of a certain window, pass the window's display start location as from and the window's upper-left coordinates as frompos. Pass the buffer's
(point-max)as to, to limit the scan to the end of the accessible portion of the buffer, and pass line and col as topos. Here's a function that does this:(defun coordinates-of-position (col line) (car (compute-motion (window-start) '(0 . 0) (point-max) (cons col line) (window-width) (cons (window-hscroll) 0) (selected-window))))When you use
compute-motionfor the minibuffer, you need to useminibuffer-prompt-widthto get the horizontal position of the beginning of the first screen line. See Minibuffer Misc.
Here are several functions concerned with balanced-parenthesis expressions (also called sexps in connection with moving across them in Emacs). The syntax table controls how these functions interpret various characters; see Syntax Tables. See Parsing Expressions, for lower-level primitives for scanning sexps or parts of sexps. For user-level commands, see Lists Commands.
This function moves forward across arg (default 1) balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.)
This function moves backward across arg (default 1) balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.)
This function moves forward out of arg (default 1) levels of parentheses. A negative argument means move backward but still to a less deep spot.
This function moves forward into arg (default 1) levels of parentheses. A negative argument means move backward but still go deeper in parentheses (−arg levels).
This function moves forward across arg (default 1) balanced expressions. Balanced expressions include both those delimited by parentheses and other kinds, such as words and string constants. For example,
---------- Buffer: foo ---------- (concat-!- "foo " (car x) y z) ---------- Buffer: foo ---------- (forward-sexp 3) => nil ---------- Buffer: foo ---------- (concat "foo " (car x) y-!- z) ---------- Buffer: foo ----------
This function moves backward across arg (default 1) balanced expressions.
This function moves back to the argth beginning of a defun. If arg is negative, this actually moves forward, but it still moves to the beginning of a defun, not to the end of one.
This function moves forward to the argth end of a defun. If arg is negative, this actually moves backward, but it still moves to the end of a defun, not to the beginning of one.
If non-
nil, this variable holds a regular expression that specifies what text can appear before the open-parenthesis that starts a defun. That is to say, a defun begins on a line that starts with a match for this regular expression, followed by a character with open-parenthesis syntax.
If this variable's value is non-
nil, an open parenthesis in column 0 is considered to be the start of a defun. If it isnil, an open parenthesis in column 0 has no special meaning. The default ist.
If non-
nil, this variable holds a function for finding the beginning of a defun. The functionbeginning-of-defuncalls this function instead of using its normal method.
If non-
nil, this variable holds a function for finding the end of a defun. The functionend-of-defuncalls this function instead of using its normal method.
The following two functions move point over a specified set of characters. For example, they are often used to skip whitespace. For related functions, see Motion and Syntax.
This function moves point in the current buffer forward, skipping over a given set of characters. It examines the character following point, then advances point if the character matches character-set. This continues until it reaches a character that does not match. The function returns the number of characters moved over.
The argument character-set is like the inside of a ‘[...]’ in a regular expression except that ‘]’ is never special and ‘\’ quotes ‘^’, ‘-’ or ‘\’. Thus,
"a-zA-Z"skips over all letters, stopping before the first nonletter, and"^a-zA-Z"skips nonletters stopping before the first letter. See Regular Expressions.If limit is supplied (it must be a number or a marker), it specifies the maximum position in the buffer that point can be skipped to. Point will stop at or before limit.
In the following example, point is initially located directly before the ‘T’. After the form is evaluated, point is located at the end of that line (between the ‘t’ of ‘hat’ and the newline). The function skips all letters and spaces, but not newlines.
---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (skip-chars-forward "a-zA-Z ") => nil ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ----------
This function moves point backward, skipping characters that match character-set, until limit. It is just like
skip-chars-forwardexcept for the direction of motion.The return value indicates the distance traveled. It is an integer that is zero or less.
It is often useful to move point “temporarily” within a localized
portion of the program, or to switch buffers temporarily. This is
called an excursion, and it is done with the save-excursion
special form. This construct initially remembers the identity of the
current buffer, and its values of point and the mark, and restores them
after the completion of the excursion.
The forms for saving and restoring the configuration of windows are described elsewhere (see Window Configurations, and see Frame Configurations).
The
save-excursionspecial form saves the identity of the current buffer and the values of point and the mark in it, evaluates forms, and finally restores the buffer and its saved values of point and the mark. All three saved values are restored even in case of an abnormal exit viathrowor error (see Nonlocal Exits).The
save-excursionspecial form is the standard way to switch buffers or move point within one part of a program and avoid affecting the rest of the program. It is used more than 4000 times in the Lisp sources of Emacs.
save-excursiondoes not save the values of point and the mark for other buffers, so changes in other buffers remain in effect aftersave-excursionexits.Likewise,
save-excursiondoes not restore window-buffer correspondences altered by functions such asswitch-to-buffer. One way to restore these correspondences, and the selected window, is to usesave-window-excursioninsidesave-excursion(see Window Configurations).The value returned by
save-excursionis the result of the last of forms, ornilif no forms are given.(save-excursion forms) == (let ((old-buf (current-buffer)) (old-pnt (point-marker)) (old-mark (copy-marker (mark-marker)))) (unwind-protect (progn forms) (set-buffer old-buf) (goto-char old-pnt) (set-marker (mark-marker) old-mark)))
Warning: Ordinary insertion of text adjacent to the saved point value relocates the saved value, just as it relocates all markers. Therefore, when the saved point value is restored, it normally comes before the inserted text.
Although save-excursion saves the location of the mark, it does
not prevent functions which modify the buffer from setting
deactivate-mark, and thus causing the deactivation of the mark
after the command finishes. See The Mark.
Narrowing means limiting the text addressable by Emacs editing commands to a limited range of characters in a buffer. The text that remains addressable is called the accessible portion of the buffer.
Narrowing is specified with two buffer positions which become the beginning and end of the accessible portion. For most editing commands and most Emacs primitives, these positions replace the values of the beginning and end of the buffer. While narrowing is in effect, no text outside the accessible portion is displayed, and point cannot move outside the accessible portion.
Values such as positions or line numbers, which usually count from the beginning of the buffer, do so despite narrowing, but the functions which use them refuse to operate on text that is inaccessible.
The commands for saving buffers are unaffected by narrowing; they save the entire buffer regardless of any narrowing.
This function sets the accessible portion of the current buffer to start at start and end at end. Both arguments should be character positions.
In an interactive call, start and end are set to the bounds of the current region (point and the mark, with the smallest first).
This function sets the accessible portion of the current buffer to include just the current page. An optional first argument move-count non-
nilmeans to move forward or backward by move-count pages and then narrow to one page. The variablepage-delimiterspecifies where pages start and end (see Standard Regexps).In an interactive call, move-count is set to the numeric prefix argument.
This function cancels any narrowing in the current buffer, so that the entire contents are accessible. This is called widening. It is equivalent to the following expression:
(narrow-to-region 1 (1+ (buffer-size)))
This special form saves the current bounds of the accessible portion, evaluates the body forms, and finally restores the saved bounds, thus restoring the same state of narrowing (or absence thereof) formerly in effect. The state of narrowing is restored even in the event of an abnormal exit via
throwor error (see Nonlocal Exits). Therefore, this construct is a clean way to narrow a buffer temporarily.The value returned by
save-restrictionis that returned by the last form in body, ornilif no body forms were given.Caution: it is easy to make a mistake when using the
save-restrictionconstruct. Read the entire description here before you try it.If body changes the current buffer,
save-restrictionstill restores the restrictions on the original buffer (the buffer whose restrictions it saved from), but it does not restore the identity of the current buffer.
save-restrictiondoes not restore point and the mark; usesave-excursionfor that. If you use bothsave-restrictionandsave-excursiontogether,save-excursionshould come first (on the outside). Otherwise, the old point value would be restored with temporary narrowing still in effect. If the old point value were outside the limits of the temporary narrowing, this would fail to restore it accurately.Here is a simple example of correct use of
save-restriction:---------- Buffer: foo ---------- This is the contents of foo This is the contents of foo This is the contents of foo-!- ---------- Buffer: foo ---------- (save-excursion (save-restriction (goto-char 1) (forward-line 2) (narrow-to-region 1 (point)) (goto-char (point-min)) (replace-string "foo" "bar"))) ---------- Buffer: foo ---------- This is the contents of bar This is the contents of bar This is the contents of foo-!- ---------- Buffer: foo ----------
A marker is a Lisp object used to specify a position in a buffer relative to the surrounding text. A marker changes its offset from the beginning of the buffer automatically whenever text is inserted or deleted, so that it stays with the two characters on either side of it.
A marker specifies a buffer and a position in that buffer. The marker can be used to represent a position in the functions that require one, just as an integer could be used. See Positions, for a complete description of positions.
A marker has two attributes: the marker position, and the marker buffer. The marker position is an integer that is equivalent (at a given time) to the marker as a position in that buffer. But the marker's position value can change often during the life of the marker. Insertion and deletion of text in the buffer relocate the marker. The idea is that a marker positioned between two characters remains between those two characters despite insertion and deletion elsewhere in the buffer. Relocation changes the integer equivalent of the marker.
Deleting text around a marker's position leaves the marker between the
characters immediately before and after the deleted text. Inserting
text at the position of a marker normally leaves the marker either in
front of or after the new text, depending on the marker's insertion
type (see Marker Insertion Types)—unless the insertion is done
with insert-before-markers (see Insertion).
Insertion and deletion in a buffer must check all the markers and relocate them if necessary. This slows processing in a buffer with a large number of markers. For this reason, it is a good idea to make a marker point nowhere if you are sure you don't need it any more. Unreferenced markers are garbage collected eventually, but until then will continue to use time if they do point somewhere.
Because it is common to perform arithmetic operations on a marker
position, most of the arithmetic operations (including + and
-) accept markers as arguments. In such cases, the marker
stands for its current position.
Here are examples of creating markers, setting markers, and moving point to markers:
;; Make a new marker that initially does not point anywhere: (setq m1 (make-marker)) => #<marker in no buffer> ;; Setm1to point between the 99th and 100th characters ;; in the current buffer: (set-marker m1 100) => #<marker at 100 in markers.texi> ;; Now insert one character at the beginning of the buffer: (goto-char (point-min)) => 1 (insert "Q") => nil ;;m1is updated appropriately. m1 => #<marker at 101 in markers.texi> ;; Two markers that point to the same position ;; are noteq, but they areequal. (setq m2 (copy-marker m1)) => #<marker at 101 in markers.texi> (eq m1 m2) => nil (equal m1 m2) => t ;; When you are finished using a marker, make it point nowhere. (set-marker m1 nil) => #<marker in no buffer>
You can test an object to see whether it is a marker, or whether it is either an integer or a marker. The latter test is useful in connection with the arithmetic functions that work with both markers and integers.
This function returns
tif object is a marker,nilotherwise. Note that integers are not markers, even though many functions will accept either a marker or an integer.
This function returns
tif object is an integer or a marker,nilotherwise.
This function returns
tif object is a number (either integer or floating point) or a marker,nilotherwise.
When you create a new marker, you can make it point nowhere, or point to the present position of point, or to the beginning or end of the accessible portion of the buffer, or to the same place as another given marker.
This function returns a newly created marker that does not point anywhere.
(make-marker) => #<marker in no buffer>
This function returns a new marker that points to the present position of point in the current buffer. See Point. For an example, see
copy-marker, below.
This function returns a new marker that points to the beginning of the accessible portion of the buffer. This will be the beginning of the buffer unless narrowing is in effect. See Narrowing.
This function returns a new marker that points to the end of the accessible portion of the buffer. This will be the end of the buffer unless narrowing is in effect. See Narrowing.
Here are examples of this function and
point-min-marker, shown in a buffer containing a version of the source file for the text of this chapter.(point-min-marker) => #<marker at 1 in markers.texi> (point-max-marker) => #<marker at 15573 in markers.texi> (narrow-to-region 100 200) => nil (point-min-marker) => #<marker at 100 in markers.texi> (point-max-marker) => #<marker at 200 in markers.texi>
If passed a marker as its argument,
copy-markerreturns a new marker that points to the same place and the same buffer as does marker-or-integer. If passed an integer as its argument,copy-markerreturns a new marker that points to position marker-or-integer in the current buffer.The new marker's insertion type is specified by the argument insertion-type. See Marker Insertion Types.
If passed an integer argument less than 1,
copy-markerreturns a new marker that points to the beginning of the current buffer. If passed an integer argument greater than the length of the buffer,copy-markerreturns a new marker that points to the end of the buffer.(copy-marker 0) => #<marker at 1 in markers.texi> (copy-marker 20000) => #<marker at 7572 in markers.texi>An error is signaled if marker is neither a marker nor an integer.
Two distinct markers are considered equal (even though not
eq) to each other if they have the same position and buffer, or
if they both point nowhere.
(setq p (point-marker))
=> #<marker at 2139 in markers.texi>
(setq q (copy-marker p))
=> #<marker at 2139 in markers.texi>
(eq p q)
=> nil
(equal p q)
=> t
This section describes the functions for accessing the components of a marker object.
This function returns the position that marker points to, or
nilif it points nowhere.
This function returns the buffer that marker points into, or
nilif it points nowhere.(setq m (make-marker)) => #<marker in no buffer> (marker-position m) => nil (marker-buffer m) => nil (set-marker m 3770 (current-buffer)) => #<marker at 3770 in markers.texi> (marker-buffer m) => #<buffer markers.texi> (marker-position m) => 3770
This function returns
tif one or more markers point at position position in the current buffer.
When you insert text directly at the place where a marker points,
there are two possible ways to relocate that marker: it can point before
the inserted text, or point after it. You can specify which one a given
marker should do by setting its insertion type. Note that use of
insert-before-markers ignores markers' insertion types, always
relocating a marker to point after the inserted text.
This function sets the insertion type of marker marker to type. If type is
t, marker will advance when text is inserted at its position. If type isnil, marker does not advance when text is inserted there.
This function reports the current insertion type of marker.
This section describes how to change the position of an existing marker. When you do this, be sure you know whether the marker is used outside of your program, and, if so, what effects will result from moving it—otherwise, confusing things may happen in other parts of Emacs.
This function moves marker to position in buffer. If buffer is not provided, it defaults to the current buffer.
If position is less than 1,
set-markermoves marker to the beginning of the buffer. If position is greater than the size of the buffer,set-markermoves marker to the end of the buffer. If position isnilor a marker that points nowhere, then marker is set to point nowhere.The value returned is marker.
(setq m (point-marker)) => #<marker at 4714 in markers.texi> (set-marker m 55) => #<marker at 55 in markers.texi> (setq b (get-buffer "foo")) => #<buffer foo> (set-marker m 0 b) => #<marker at 1 in foo>
One special marker in each buffer is designated the mark. It
records a position for the user for the sake of commands such as
kill-region and indent-rigidly. Lisp programs should set
the mark only to values that have a potential use to the user, and never
for their own internal purposes. For example, the replace-regexp
command sets the mark to the value of point before doing any
replacements, because this enables the user to move back there
conveniently after the replace is finished.
Many commands are designed so that when called interactively they
operate on the text between point and the mark. If you are writing such
a command, don't examine the mark directly; instead, use
interactive with the ‘r’ specification. This provides the
values of point and the mark as arguments to the command in an
interactive call, but permits other Lisp programs to specify arguments
explicitly. See Interactive Codes.
Each buffer has its own value of the mark that is independent of the value of the mark in other buffers. When a buffer is created, the mark exists but does not point anywhere. We consider this state as “the absence of a mark in that buffer.”
Once the mark “exists” in a buffer, it normally never ceases to
exist. However, it may become inactive, if Transient Mark mode is
enabled. The variable mark-active, which is always buffer-local
in all buffers, indicates whether the mark is active: non-nil
means yes. A command can request deactivation of the mark upon return
to the editor command loop by setting deactivate-mark to a
non-nil value (but this causes deactivation only if Transient
Mark mode is enabled).
The main motivation for using Transient Mark mode is that this mode also enables highlighting of the region when the mark is active. See Display.
In addition to the mark, each buffer has a mark ring which is a
list of markers containing previous values of the mark. When editing
commands change the mark, they should normally save the old value of the
mark on the mark ring. The variable mark-ring-max specifies the
maximum number of entries in the mark ring; once the list becomes this
long, adding a new element deletes the last element.
There is also a separate global mark ring, but that is used only in a few particular user-level commands, and is not relevant to Lisp programming. So we do not describe it here.
This function returns the current buffer's mark position as an integer.
If the mark is inactive,
marknormally signals an error. However, if force is non-nil, thenmarkreturns the mark position anyway—ornil, if the mark is not yet set for this buffer.
This function returns the current buffer's mark. This is the very marker that records the mark location inside Emacs, not a copy. Therefore, changing this marker's position will directly affect the position of the mark. Don't do it unless that is the effect you want.
(setq m (mark-marker)) => #<marker at 3420 in markers.texi> (set-marker m 100) => #<marker at 100 in markers.texi> (mark-marker) => #<marker at 100 in markers.texi>Like any marker, this marker can be set to point at any buffer you like. We don't recommend that you make it point at any buffer other than the one of which it is the mark. If you do, it will yield perfectly consistent, but rather odd, results.
This function sets the mark to position, and activates the mark. The old value of the mark is not pushed onto the mark ring.
Please note: Use this function only if you want the user to see that the mark has moved, and you want the previous mark position to be lost. Normally, when a new mark is set, the old one should go on the
mark-ring. For this reason, most applications should usepush-markandpop-mark, notset-mark.Novice Emacs Lisp programmers often try to use the mark for the wrong purposes. The mark saves a location for the user's convenience. An editing command should not alter the mark unless altering the mark is part of the user-level functionality of the command. (And, in that case, this effect should be documented.) To remember a location for internal use in the Lisp program, store it in a Lisp variable. For example:
(let ((beg (point))) (forward-line 1) (delete-region beg (point))).
This function sets the current buffer's mark to position, and pushes a copy of the previous mark onto
mark-ring. If position isnil, then the value of point is used.push-markreturnsnil.The function
push-marknormally does not activate the mark. To do that, specifytfor the argument activate.A ‘Mark set’ message is displayed unless nomsg is non-
nil.
This function pops off the top element of
mark-ringand makes that mark become the buffer's actual mark. This does not move point in the buffer, and it does nothing ifmark-ringis empty. It deactivates the mark.The return value is not meaningful.
This variable if non-
nilenables Transient Mark mode, in which every buffer-modifying primitive setsdeactivate-mark. The consequence of this is that commands that modify the buffer normally make the mark inactive.
If this is non-
nil, Lisp programs and the Emacs user can use the mark even when it is inactive. This option affects the behavior of Transient Mark mode. When the option is non-nil, deactivation of the mark turns off region highlighting, but commands that use the mark behave as if the mark were still active.
If an editor command sets this variable non-
nil, then the editor command loop deactivates the mark after the command returns (if Transient Mark mode is enabled). All the primitives that change the buffer setdeactivate-mark, to deactivate the mark when the command is finished.
This function deactivates the mark, if Transient Mark mode is enabled. Otherwise it does nothing.
The mark is active when this variable is non-
nil. This variable is always buffer-local in each buffer.
These normal hooks are run, respectively, when the mark becomes active and when it becomes inactive. The hook
activate-mark-hookis also run at the end of a command if the mark is active and it is possible that the region may have changed.
The value of this buffer-local variable is the list of saved former marks of the current buffer, most recent first.
mark-ring => (#<marker at 11050 in markers.texi> #<marker at 10832 in markers.texi> ...)
The value of this variable is the maximum size of
mark-ring. If more marks than this are pushed onto themark-ring,push-markdiscards an old mark when it adds a new one.
The text between point and the mark is known as the region. Various functions operate on text delimited by point and the mark, but only those functions specifically related to the region itself are described here.
This function returns the position of the beginning of the region (as an integer). This is the position of either point or the mark, whichever is smaller.
If the mark does not point anywhere, an error is signaled.
This function returns the position of the end of the region (as an integer). This is the position of either point or the mark, whichever is larger.
If the mark does not point anywhere, an error is signaled.
Few programs need to use the region-beginning and
region-end functions. A command designed to operate on a region
should normally use interactive with the ‘r’ specification
to find the beginning and end of the region. This lets other Lisp
programs specify the bounds explicitly as arguments. (See Interactive Codes.)
This chapter describes the functions that deal with the text in a buffer. Most examine, insert, or delete text in the current buffer, often operating at point or on text adjacent to point. Many are interactive. All the functions that change the text provide for undoing the changes (see Undo).
Many text-related functions operate on a region of text defined by two
buffer positions passed in arguments named start and end.
These arguments should be either markers (see Markers) or numeric
character positions (see Positions). The order of these arguments
does not matter; it is all right for start to be the end of the
region and end the beginning. For example, (delete-region 1
10) and (delete-region 10 1) are equivalent. An
args-out-of-range error is signaled if either start or
end is outside the accessible portion of the buffer. In an
interactive call, point and the mark are used for these arguments.
Throughout this chapter, “text” refers to the characters in the buffer, together with their properties (when relevant). Keep in mind that point is always between two characters, and the cursor appears on the character after point.
Many functions are provided to look at the characters around point.
Several simple functions are described here. See also looking-at
in Regexp Search.
This function returns the character in the current buffer at (i.e., immediately after) position position. If position is out of range for this purpose, either before the beginning of the buffer, or at or beyond the end, then the value is
nil. The default for position is point.In the following example, assume that the first character in the buffer is ‘@’:
(char-to-string (char-after 1)) => "@"
This function returns the character in the current buffer immediately before position position. If position is out of range for this purpose, either before the beginning of the buffer, or at or beyond the end, then the value is
nil. The default for position is point.
This function returns the character following point in the current buffer. This is similar to
(char-after (point)). However, if point is at the end of the buffer, thenfollowing-charreturns 0.Remember that point is always between characters, and the terminal cursor normally appears over the character following point. Therefore, the character returned by
following-charis the character the cursor is over.In this example, point is between the ‘a’ and the ‘c’.
---------- Buffer: foo ---------- Gentlemen may cry ``Pea-!-ce! Peace!,'' but there is no peace. ---------- Buffer: foo ---------- (char-to-string (preceding-char)) => "a" (char-to-string (following-char)) => "c"
This function returns the character preceding point in the current buffer. See above, under
following-char, for an example. If point is at the beginning of the buffer,preceding-charreturns 0.
This function returns
tif point is at the beginning of the buffer. If narrowing is in effect, this means the beginning of the accessible portion of the text. See alsopoint-minin Point.
This function returns
tif point is at the end of the buffer. If narrowing is in effect, this means the end of accessible portion of the text. See alsopoint-maxin See Point.
This function returns
tif point is at the beginning of a line. See Text Lines. The beginning of the buffer (or of its accessible portion) always counts as the beginning of a line.
This function returns
tif point is at the end of a line. The end of the buffer (or of its accessible portion) is always considered the end of a line.
This section describes two functions that allow a Lisp program to convert any portion of the text in the buffer into a string.
This function returns a string containing a copy of the text of the region defined by positions start and end in the current buffer. If the arguments are not positions in the accessible portion of the buffer,
buffer-substringsignals anargs-out-of-rangeerror.It is not necessary for start to be less than end; the arguments can be given in either order. But most often the smaller argument is written first.
If the text being copied has any text properties, these are copied into the string along with the characters they belong to. See Text Properties. However, overlays (see Overlays) in the buffer and their properties are ignored, not copied.
---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-substring 1 10) => "This is t" (buffer-substring (point-max) 10) => "he contents of buffer foo "
This is like
buffer-substring, except that it does not copy text properties, just the characters themselves. See Text Properties.
This function returns the contents of the entire accessible portion of the current buffer as a string. It is equivalent to
(buffer-substring (point-min) (point-max))---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-string) => "This is the contents of buffer foo "
Return the thing around or next to point, as a string.
The argument thing is a symbol which specifies a kind of syntactic entity. Possibilities include
symbol,list,sexp,defun,filename,url,word,sentence,whitespace,line,page, and others.---------- Buffer: foo ---------- Gentlemen may cry ``Pea-!-ce! Peace!,'' but there is no peace. ---------- Buffer: foo ---------- (thing-at-point 'word) => "Peace" (thing-at-point 'line) => "Gentlemen may cry ``Peace! Peace!,''\n" (thing-at-point 'whitespace) => nil
This function lets you compare portions of the text in a buffer, without copying them into strings first.
This function lets you compare two substrings of the same buffer or two different buffers. The first three arguments specify one substring, giving a buffer and two positions within the buffer. The last three arguments specify the other substring in the same way. You can use
nilfor buffer1, buffer2, or both to stand for the current buffer.The value is negative if the first substring is less, positive if the first is greater, and zero if they are equal. The absolute value of the result is one plus the index of the first differing characters within the substrings.
This function ignores case when comparing characters if
case-fold-searchis non-nil. It always ignores text properties.Suppose the current buffer contains the text ‘foobarbar haha!rara!’; then in this example the two substrings are ‘rbar ’ and ‘rara!’. The value is 2 because the first substring is greater at the second character.
(compare-buffer-substrings nil 6 11 nil 16 21) => 2
Insertion means adding new text to a buffer. The inserted text goes at point—between the character before point and the character after point. Some insertion functions leave point before the inserted text, while other functions leave it after. We call the former insertion after point and the latter insertion before point.
Insertion relocates markers that point at positions after the
insertion point, so that they stay with the surrounding text
(see Markers). When a marker points at the place of insertion,
insertion may or may not relocate the marker, depending on the marker's
insertion type (see Marker Insertion Types). Certain special
functions such as insert-before-markers relocate all such markers
to point after the inserted text, regardless of the markers' insertion
type.
Insertion functions signal an error if the current buffer is read-only or if they insert within read-only text.
These functions copy text characters from strings and buffers along with their properties. The inserted characters have exactly the same properties as the characters they were copied from. By contrast, characters specified as separate arguments, not part of a string or buffer, inherit their text properties from the neighboring text.
The insertion functions convert text from unibyte to multibyte in order to insert in a multibyte buffer, and vice versa—if the text comes from a string or from a buffer. However, they do not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. See Converting Representations.
This function inserts the strings and/or characters args into the current buffer, at point, moving point forward. In other words, it inserts the text before point. An error is signaled unless all args are either strings or characters. The value is
nil.
This function inserts the strings and/or characters args into the current buffer, at point, moving point forward. An error is signaled unless all args are either strings or characters. The value is
nil.This function is unlike the other insertion functions in that it relocates markers initially pointing at the insertion point, to point after the inserted text. If an overlay begins the insertion point, the inserted text falls outside the overlay; if a nonempty overlay ends at the insertion point, the inserted text falls inside that overlay.
This function inserts count instances of character into the current buffer before point. The argument count should be a number (
nilmeans 1), and character must be a character. The value isnil.This function does not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. See Converting Representations.
If inherit is non-
nil, then the inserted characters inherit sticky text properties from the two characters before and after the insertion point. See Sticky Properties.
This function inserts a portion of buffer from-buffer-or-name (which must already exist) into the current buffer before point. The text inserted is the region from start and end. (These arguments default to the beginning and end of the accessible portion of that buffer.) This function returns
nil.In this example, the form is executed with buffer ‘bar’ as the current buffer. We assume that buffer ‘bar’ is initially empty.
---------- Buffer: foo ---------- We hold these truths to be self-evident, that all ---------- Buffer: foo ---------- (insert-buffer-substring "foo" 1 20) => nil ---------- Buffer: bar ---------- We hold these truth-!- ---------- Buffer: bar ----------
See Sticky Properties, for other insertion functions that inherit text properties from the nearby text in addition to inserting it. Whitespace inserted by indentation functions also inherits text properties.
This section describes higher-level commands for inserting text, commands intended primarily for the user but useful also in Lisp programs.
This command inserts the entire contents of from-buffer-or-name (which must exist) into the current buffer after point. It leaves the mark after the inserted text. The value is
nil.
This command inserts the last character typed; it does so count times, before point, and returns
nil. Most printing characters are bound to this command. In routine use,self-insert-commandis the most frequently called function in Emacs, but programs rarely use it except to install it on a keymap.In an interactive call, count is the numeric prefix argument.
This command calls
auto-fill-functionwhenever that is non-niland the character inserted is in the tableauto-fill-chars(see Auto Filling).This command performs abbrev expansion if Abbrev mode is enabled and the inserted character does not have word-constituent syntax. (See Abbrevs, and Syntax Class Table.)
This is also responsible for calling
blink-paren-functionwhen the inserted character has close parenthesis syntax (see Blinking).Do not try substituting your own definition of
self-insert-commandfor the standard one. The editor command loop handles this function specially.
This command inserts newlines into the current buffer before point. If number-of-newlines is supplied, that many newline characters are inserted.
This function calls
auto-fill-functionif the current column number is greater than the value offill-columnand number-of-newlines isnil. Typically whatauto-fill-functiondoes is insert a newline; thus, the overall result in this case is to insert two newlines at different places: one at point, and another earlier in the line.newlinedoes not auto-fill if number-of-newlines is non-nil.This command indents to the left margin if that is not zero. See Margins.
The value returned is
nil. In an interactive call, count is the numeric prefix argument.
This command splits the current line, moving the portion of the line after point down vertically so that it is on the next line directly below where it was before. Whitespace is inserted as needed at the beginning of the lower line, using the
indent-tofunction.split-linereturns the position of point.Programs hardly ever use this function.
This variable controls whether overwrite mode is in effect. The value should be
overwrite-mode-textual,overwrite-mode-binary, ornil.overwrite-mode-textualspecifies textual overwrite mode (treats newlines and tabs specially), andoverwrite-mode-binaryspecifies binary overwrite mode (treats newlines and tabs like any other characters).
Deletion means removing part of the text in a buffer, without saving it in the kill ring (see The Kill Ring). Deleted text can't be yanked, but can be reinserted using the undo mechanism (see Undo). Some deletion functions do save text in the kill ring in some special cases.
All of the deletion functions operate on the current buffer, and all
return a value of nil.
This function deletes the entire text of the current buffer, leaving it empty. If the buffer is read-only, it signals a
buffer-read-onlyerror; if some of the text in it is read-only, it signals atext-read-onlyerror. Otherwise, it deletes the text without asking for any confirmation. It returnsnil.Normally, deleting a large amount of text from a buffer inhibits further auto-saving of that buffer “because it has shrunk”. However,
erase-bufferdoes not do this, the idea being that the future text is not really related to the former text, and its size should not be compared with that of the former text.
This command deletes the text between positions start and end in the current buffer, and returns
nil. If point was inside the deleted region, its value afterward is start. Otherwise, point relocates with the surrounding text, as markers do.
This function deletes the text between positions start and end in the current buffer, and returns a string containing the text just deleted.
If point was inside the deleted region, its value afterward is start. Otherwise, point relocates with the surrounding text, as markers do.
This command deletes count characters directly after point, or before point if count is negative. If killp is non-
nil, then it saves the deleted characters in the kill ring.In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always
nil.
This command deletes count characters directly before point, or after point if count is negative. If killp is non-
nil, then it saves the deleted characters in the kill ring.In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always
nil.
This command deletes count characters backward, changing tabs into spaces. When the next character to be deleted is a tab, it is first replaced with the proper number of spaces to preserve alignment and then one of those spaces is deleted instead of the tab. If killp is non-
nil, then the command saves the deleted characters in the kill ring.Conversion of tabs to spaces happens only if count is positive. If it is negative, exactly −count characters after point are deleted.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always
nil.
This option specifies how
backward-delete-char-untabifyshould deal with whitespace. Possible values includeuntabify, the default, meaning convert a tab to many spaces and delete one;hungry, meaning delete all the whitespace characters before point with one command, andnil, meaning do nothing special for whitespace characters.
This section describes higher-level commands for deleting text, commands intended primarily for the user but useful also in Lisp programs.
This function deletes all spaces and tabs around point. It returns
nil.In the following examples, we call
delete-horizontal-spacefour times, once on each line, with point between the second and third characters on the line each time.---------- Buffer: foo ---------- I -!-thought I -!- thought We-!- thought Yo-!-u thought ---------- Buffer: foo ---------- (delete-horizontal-space) ; Four times. => nil ---------- Buffer: foo ---------- Ithought Ithought Wethought You thought ---------- Buffer: foo ----------
This function joins the line point is on to the previous line, deleting any whitespace at the join and in some cases replacing it with one space. If join-following-p is non-
nil,delete-indentationjoins this line to the following line instead. The function returnsnil.If there is a fill prefix, and the second of the lines being joined starts with the prefix, then
delete-indentationdeletes the fill prefix before joining the lines. See Margins.In the example below, point is located on the line starting ‘events’, and it makes no difference if there are trailing spaces in the preceding line.
---------- Buffer: foo ---------- When in the course of human -!- events, it becomes necessary ---------- Buffer: foo ---------- (delete-indentation) => nil ---------- Buffer: foo ---------- When in the course of human-!- events, it becomes necessary ---------- Buffer: foo ----------After the lines are joined, the function
fixup-whitespaceis responsible for deciding whether to leave a space at the junction.
This function replaces all the whitespace surrounding point with either one space or no space, according to the context. It returns
nil.At the beginning or end of a line, the appropriate amount of space is none. Before a character with close parenthesis syntax, or after a character with open parenthesis or expression-prefix syntax, no space is also appropriate. Otherwise, one space is appropriate. See Syntax Class Table.
In the example below,
fixup-whitespaceis called the first time with point before the word ‘spaces’ in the first line. For the second invocation, point is directly after the ‘(’.---------- Buffer: foo ---------- This has too many -!-spaces This has too many spaces at the start of (-!- this list) ---------- Buffer: foo ---------- (fixup-whitespace) => nil (fixup-whitespace) => nil ---------- Buffer: foo ---------- This has too many spaces This has too many spaces at the start of (this list) ---------- Buffer: foo ----------
This command replaces any spaces and tabs around point with a single space. It returns
nil.
This function deletes blank lines surrounding point. If point is on a blank line with one or more blank lines before or after it, then all but one of them are deleted. If point is on an isolated blank line, then it is deleted. If point is on a nonblank line, the command deletes all blank lines following it.
A blank line is defined as a line containing only tabs and spaces.
delete-blank-linesreturnsnil.
Kill functions delete text like the deletion functions, but save it so that the user can reinsert it by yanking. Most of these functions have ‘kill-’ in their name. By contrast, the functions whose names start with ‘delete-’ normally do not save text for yanking (though they can still be undone); these are “deletion” functions.
Most of the kill commands are primarily for interactive use, and are not described here. What we do describe are the functions provided for use in writing such commands. You can use these functions to write commands for killing text. When you need to delete text for internal purposes within a Lisp function, you should normally use deletion functions, so as not to disturb the kill ring contents. See Deletion.
Killed text is saved for later yanking in the kill ring. This
is a list that holds a number of recent kills, not just the last text
kill. We call this a “ring” because yanking treats it as having
elements in a cyclic order. The list is kept in the variable
kill-ring, and can be operated on with the usual functions for
lists; there are also specialized functions, described in this section,
that treat it as a ring.
Some people think this use of the word “kill” is unfortunate, since it refers to operations that specifically do not destroy the entities “killed”. This is in sharp contrast to ordinary life, in which death is permanent and “killed” entities do not come back to life. Therefore, other metaphors have been proposed. For example, the term “cut ring” makes sense to people who, in pre-computer days, used scissors and paste to cut up and rearrange manuscripts. However, it would be difficult to change the terminology now.
The kill ring records killed text as strings in a list, most recent first. A short kill ring, for example, might look like this:
("some text" "a different piece of text" "even older text")
When the list reaches kill-ring-max entries in length, adding a
new entry automatically deletes the last entry.
When kill commands are interwoven with other commands, each kill command makes a new entry in the kill ring. Multiple kill commands in succession build up a single kill-ring entry, which would be yanked as a unit; the second and subsequent consecutive kill commands add text to the entry made by the first one.
For yanking, one entry in the kill ring is designated the “front” of the ring. Some yank commands “rotate” the ring by designating a different element as the “front.” But this virtual rotation doesn't change the list itself—the most recent entry always comes first in the list.
kill-region is the usual subroutine for killing text. Any
command that calls this function is a “kill command” (and should
probably have ‘kill’ in its name). kill-region puts the
newly killed text in a new element at the beginning of the kill ring or
adds it to the most recent element. It determines automatically (using
last-command) whether the previous command was a kill command,
and if so appends the killed text to the most recent entry.
This function kills the text in the region defined by start and end. The text is deleted but saved in the kill ring, along with its text properties. The value is always
nil.In an interactive call, start and end are point and the mark.
If the buffer or text is read-only,
kill-regionmodifies the kill ring just the same, then signals an error without modifying the buffer. This is convenient because it lets the user use a series of kill commands to copy text from a read-only buffer into the kill ring.
If this option is non-
nil,kill-regiondoes not signal an error if the buffer or text is read-only. Instead, it simply returns, updating the kill ring but not changing the buffer.
This command saves the region defined by start and end on the kill ring (including text properties), but does not delete the text from the buffer. It returns
nil. It also indicates the extent of the text copied by moving the cursor momentarily, or by displaying a message in the echo area.The command does not set
this-commandtokill-region, so a subsequent kill command does not append to the same kill ring entry.Don't call
copy-region-as-killin Lisp programs unless you aim to support Emacs 18. For newer Emacs versions, it is better to usekill-neworkill-appendinstead. See Low-Level Kill Ring.
Yanking means reinserting an entry of previously killed text from the kill ring. The text properties are copied too.
This command inserts before point the text in the first entry in the kill ring. It positions the mark at the beginning of that text, and point at the end.
If arg is a list (which occurs interactively when the user types C-u with no digits), then
yankinserts the text as described above, but puts point before the yanked text and puts the mark after it.If arg is a number, then
yankinserts the argth most recently killed text—the argth element of the kill ring list.
yankdoes not alter the contents of the kill ring or rotate it. It returnsnil.
This command replaces the just-yanked entry from the kill ring with a different entry from the kill ring.
This is allowed only immediately after a
yankor anotheryank-pop. At such a time, the region contains text that was just inserted by yanking.yank-popdeletes that text and inserts in its place a different piece of killed text. It does not add the deleted text to the kill ring, since it is already in the kill ring somewhere.If arg is
nil, then the replacement text is the previous element of the kill ring. If arg is numeric, the replacement is the argth previous kill. If arg is negative, a more recent kill is the replacement.The sequence of kills in the kill ring wraps around, so that after the oldest one comes the newest one, and before the newest one goes the oldest.
The return value is always
nil.
These functions and variables provide access to the kill ring at a lower level, but still convenient for use in Lisp programs, because they take care of interaction with window system selections (see Window System Selections).
The function
current-killrotates the yanking pointer, which designates the “front” of the kill ring, by n places (from newer kills to older ones), and returns the text at that place in the ring.If the optional second argument do-not-move is non-
nil, thencurrent-killdoesn't alter the yanking pointer; it just returns the nth kill, counting from the current yanking pointer.If n is zero, indicating a request for the latest kill,
current-killcalls the value ofinterprogram-paste-function(documented below) before consulting the kill ring.
This function puts the text string into the kill ring as a new entry at the front of the ring. It discards the oldest entry if appropriate. It also invokes the value of
interprogram-cut-function(see below).
This function appends the text string to the first entry in the kill ring. Normally string goes at the end of the entry, but if before-p is non-
nil, it goes at the beginning. This function also invokes the value ofinterprogram-cut-function(see below).
This variable provides a way of transferring killed text from other programs, when you are using a window system. Its value should be
nilor a function of no arguments.If the value is a function,
current-killcalls it to get the “most recent kill”. If the function returns a non-nilvalue, then that value is used as the “most recent kill”. If it returnsnil, then the first element ofkill-ringis used.The normal use of this hook is to get the window system's primary selection as the most recent kill, even if the selection belongs to another application. See Window System Selections.
This variable provides a way of communicating killed text to other programs, when you are using a window system. Its value should be
nilor a function of one argument.If the value is a function,
kill-newandkill-appendcall it with the new first element of the kill ring as an argument.The normal use of this hook is to set the window system's primary selection from the newly killed text. See Window System Selections.
The variable kill-ring holds the kill ring contents, in the
form of a list of strings. The most recent kill is always at the front
of the list.
The kill-ring-yank-pointer variable points to a link in the
kill ring list, whose car is the text to yank next. We say it
identifies the “front” of the ring. Moving
kill-ring-yank-pointer to a different link is called
rotating the kill ring. We call the kill ring a “ring” because
the functions that move the yank pointer wrap around from the end of the
list to the beginning, or vice-versa. Rotation of the kill ring is
virtual; it does not change the value of kill-ring.
Both kill-ring and kill-ring-yank-pointer are Lisp
variables whose values are normally lists. The word “pointer” in the
name of the kill-ring-yank-pointer indicates that the variable's
purpose is to identify one element of the list for use by the next yank
command.
The value of kill-ring-yank-pointer is always eq to one
of the links in the kill ring list. The element it identifies is the
car of that link. Kill commands, which change the kill ring, also
set this variable to the value of kill-ring. The effect is to
rotate the ring so that the newly killed text is at the front.
Here is a diagram that shows the variable kill-ring-yank-pointer
pointing to the second entry in the kill ring ("some text" "a
different piece of text" "yet older text").
kill-ring ---- kill-ring-yank-pointer
| |
| v
| --- --- --- --- --- ---
--> | | |------> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
| | -->"yet older text"
| |
| --> "a different piece of text"
|
--> "some text"
This state of affairs might occur after C-y (yank)
immediately followed by M-y (yank-pop).
This variable holds the list of killed text sequences, most recently killed first.
This variable's value indicates which element of the kill ring is at the “front” of the ring for yanking. More precisely, the value is a tail of the value of
kill-ring, and its car is the kill string that C-y should yank.
The value of this variable is the maximum length to which the kill ring can grow, before elements are thrown away at the end. The default value for
kill-ring-maxis 30.
Most buffers have an undo list, which records all changes made
to the buffer's text so that they can be undone. (The buffers that
don't have one are usually special-purpose buffers for which Emacs
assumes that undoing is not useful.) All the primitives that modify the
text in the buffer automatically add elements to the front of the undo
list, which is in the variable buffer-undo-list.
This variable's value is the undo list of the current buffer. A value of
tdisables the recording of undo information.
Here are the kinds of elements an undo list can have:
(beg . end)(text . position)(abs position).
(t high . low)primitive-undo uses those
values to determine whether to mark the buffer as unmodified once again;
it does so only if the file's modification time matches those numbers.
(nil property value beg . end) (put-text-property beg end property value)
(marker . adjustment)nilThis function places a boundary element in the undo list. The undo command stops at such a boundary, and successive undo commands undo to earlier and earlier boundaries. This function returns
nil.The editor command loop automatically creates an undo boundary before each key sequence is executed. Thus, each undo normally undoes the effects of one command. Self-inserting input characters are an exception. The command loop makes a boundary for the first such character; the next 19 consecutive self-inserting input characters do not make boundaries, and then the 20th does, and so on as long as self-inserting characters continue.
All buffer modifications add a boundary whenever the previous undoable change was made in some other buffer. This is to ensure that each command makes a boundary in each buffer where it makes changes.
Calling this function explicitly is useful for splitting the effects of a command into more than one unit. For example,
query-replacecallsundo-boundaryafter each replacement, so that the user can undo individual replacements one by one.
This is the basic function for undoing elements of an undo list. It undoes the first count elements of list, returning the rest of list. You could write this function in Lisp, but it is convenient to have it in C.
primitive-undoadds elements to the buffer's undo list when it changes the buffer. Undo commands avoid confusion by saving the undo list value at the beginning of a sequence of undo operations. Then the undo operations use and update the saved value. The new elements added by undoing are not part of this saved value, so they don't interfere with continuing to undo.
This section describes how to enable and disable undo information for a given buffer. It also explains how the undo list is truncated automatically so it doesn't get too big.
Recording of undo information in a newly created buffer is normally
enabled to start with; but if the buffer name starts with a space, the
undo recording is initially disabled. You can explicitly enable or
disable undo recording with the following two functions, or by setting
buffer-undo-list yourself.
This command enables recording undo information for buffer buffer-or-name, so that subsequent changes can be undone. If no argument is supplied, then the current buffer is used. This function does nothing if undo recording is already enabled in the buffer. It returns
nil.In an interactive call, buffer-or-name is the current buffer. You cannot specify any other buffer.
This function discards the undo list of buffer, and disables further recording of undo information. As a result, it is no longer possible to undo either previous changes or any subsequent changes. If the undo list of buffer is already disabled, this function has no effect.
This function returns
nil.The name
buffer-flush-undois not considered obsolete, but the preferred name isbuffer-disable-undo.
As editing continues, undo lists get longer and longer. To prevent
them from using up all available memory space, garbage collection trims
them back to size limits you can set. (For this purpose, the “size”
of an undo list measures the cons cells that make up the list, plus the
strings of deleted text.) Two variables control the range of acceptable
sizes: undo-limit and undo-strong-limit.
This is the soft limit for the acceptable size of an undo list. The change group at which this size is exceeded is the last one kept.
This is the upper limit for the acceptable size of an undo list. The change group at which this size is exceeded is discarded itself (along with all older change groups). There is one exception: the very latest change group is never discarded no matter how big it is.
Filling means adjusting the lengths of lines (by moving the line
breaks) so that they are nearly (but no greater than) a specified
maximum width. Additionally, lines can be justified, which means
inserting spaces to make the left and/or right margins line up
precisely. The width is controlled by the variable fill-column.
For ease of reading, lines should be no longer than 70 or so columns.
You can use Auto Fill mode (see Auto Filling) to fill text automatically as you insert it, but changes to existing text may leave it improperly filled. Then you must fill the text explicitly.
Most of the commands in this section return values that are not
meaningful. All the functions that do filling take note of the current
left margin, current right margin, and current justification style
(see Margins). If the current justification style is
none, the filling functions don't actually do anything.
Several of the filling functions have an argument justify.
If it is non-nil, that requests some kind of justification. It
can be left, right, full, or center, to
request a specific style of justification. If it is t, that
means to use the current justification style for this part of the text
(see current-justification, below). Any other value is treated
as full.
When you call the filling functions interactively, using a prefix
argument implies the value full for justify.
This command fills the paragraph at or after point. If justify is non-
nil, each line is justified as well. It uses the ordinary paragraph motion commands to find paragraph boundaries. See Paragraphs.
This command fills each of the paragraphs in the region from start to end. It justifies as well if justify is non-
nil.If nosqueeze is non-
nil, that means to leave whitespace other than line breaks untouched. If to-eop is non-nil, that means to keep filling to the end of the paragraph—or the next hard newline, ifuse-hard-newlinesis enabled (see below).The variable
paragraph-separatecontrols how to distinguish paragraphs. See Standard Regexps.
This command fills each paragraph in the region according to its individual fill prefix. Thus, if the lines of a paragraph were indented with spaces, the filled paragraph will remain indented in the same fashion.
The first two arguments, start and end, are the beginning and end of the region to be filled. The third and fourth arguments, justify and citation-regexp, are optional. If justify is non-
nil, the paragraphs are justified as well as filled. If citation-regexp is non-nil, it means the function is operating on a mail message and therefore should not fill the header lines. If citation-regexp is a string, it is used as a regular expression; if it matches the beginning of a line, that line is treated as a citation marker.Ordinarily,
fill-individual-paragraphsregards each change in indentation as starting a new paragraph. Iffill-individual-varying-indentis non-nil, then only separator lines separate paragraphs. That mode can handle indented paragraphs with additional indentation on the first line.
This variable alters the action of
fill-individual-paragraphsas described above.
This command considers a region of text as a single paragraph and fills it. If the region was made up of many paragraphs, the blank lines between paragraphs are removed. This function justifies as well as filling when justify is non-
nil.In an interactive call, any prefix argument requests justification.
If nosqueeze is non-
nil, that means to leave whitespace other than line breaks untouched. If squeeze-after is non-nil, it specifies a position in the region, and means don't canonicalize spaces before that position.In Adaptive Fill mode, this command calls
fill-context-prefixto choose a fill prefix by default. See Adaptive Fill.
This command inserts spaces between the words of the current line so that the line ends exactly at
fill-column. It returnsnil.The argument how, if non-
nilspecifies explicitly the style of justification. It can beleft,right,full,center, ornone. If it ist, that means to do follow specified justification style (seecurrent-justification, below).nilmeans to do full justification.If eop is non-
nil, that means do left-justification ifcurrent-justificationspecifies full justification. This is used for the last line of a paragraph; even if the paragraph as a whole is fully justified, the last line should not be.If nosqueeze is non-
nil, that means do not change interior whitespace.
This variable's value specifies the style of justification to use for text that doesn't specify a style with a text property. The possible values are
left,right,full,center, ornone. The default value isleft.
This function returns the proper justification style to use for filling the text around point.
If this variable is non-
nil, a period followed by just one space does not count as the end of a sentence, and the filling functions avoid breaking the line at such a place.
This variable provides a way for major modes to override the filling of paragraphs. If the value is non-
nil,fill-paragraphcalls this function to do the work. If the function returns a non-nilvalue,fill-paragraphassumes the job is done, and immediately returns that value.The usual use of this feature is to fill comments in programming language modes. If the function needs to fill a paragraph in the usual way, it can do so as follows:
(let ((fill-paragraph-function nil)) (fill-paragraph arg))
If this variable is non-
nil, the filling functions do not delete newlines that have thehardtext property. These “hard newlines” act as paragraph separators.
This buffer-local variable specifies a string of text that appears at the beginning of normal text lines and should be disregarded when filling them. Any line that fails to start with the fill prefix is considered the start of a paragraph; so is any line that starts with the fill prefix followed by additional whitespace. Lines that start with the fill prefix but no additional whitespace are ordinary text lines that can be filled together. The resulting filled lines also start with the fill prefix.
The fill prefix follows the left margin whitespace, if any.
This buffer-local variable specifies the maximum width of filled lines. Its value should be an integer, which is a number of columns. All the filling, justification, and centering commands are affected by this variable, including Auto Fill mode (see Auto Filling).
As a practical matter, if you are writing text for other people to read, you should set
fill-columnto no more than 70. Otherwise the line will be too long for people to read comfortably, and this can make the text seem clumsy.
The value of this variable is the default value for
fill-columnin buffers that do not override it. This is the same as(default-value 'fill-column).The default value for
default-fill-columnis 70.
This sets the
left-marginproperty on the text from from to to to the value margin. If Auto Fill mode is enabled, this command also refills the region to fit the new margin.
This sets the
right-marginproperty on the text from from to to to the value margin. If Auto Fill mode is enabled, this command also refills the region to fit the new margin.
This function returns the proper left margin value to use for filling the text around point. The value is the sum of the
left-marginproperty of the character at the start of the current line (or zero if none), and the value of the variableleft-margin.
This function returns the proper fill column value to use for filling the text around point. The value is the value of the
fill-columnvariable, minus the value of theright-marginproperty of the character after point.
This function moves point to the left margin of the current line. The column moved to is determined by calling the function
current-left-margin. If the argument n is non-nil,move-to-left-marginmoves forward n−1 lines first.If force is non-
nil, that says to fix the line's indentation if that doesn't match the left margin value.
This function removes left margin indentation from the text between from and to. The amount of indentation to delete is determined by calling
current-left-margin. In no case does this function delete non-whitespace. If from and to are omitted, they default to the whole buffer.
This is the default
indent-line-function, used in Fundamental mode, Text mode, etc. Its effect is to adjust the indentation at the beginning of the current line to the value specified by the variableleft-margin. This may involve either inserting or deleting whitespace.
This variable specifies the base left margin column. In Fundamental mode, C-j indents to this column. This variable automatically becomes buffer-local when set in any fashion.
This variable gives major modes a way to specify not to break a line at certain places. Its value should be a function. This function is called during filling, with no arguments and with point located at the place where a break is being considered. If the function returns non-
nil, then the line won't be broken there.
Adaptive Fill mode chooses a fill prefix automatically from the text in each paragraph being filled.
Adaptive Fill mode is enabled when this variable is non-
nil. It istby default.
This function implements the heart of Adaptive Fill mode; it chooses a fill prefix based on the text between from and to. It does this by looking at the first two lines of the paragraph, based on the variables described below.
This variable holds a regular expression to control Adaptive Fill mode. Adaptive Fill mode matches this regular expression against the text starting after the left margin whitespace (if any) on a line; the characters it matches are that line's candidate for the fill prefix.
In a one-line paragraph, if the candidate fill prefix matches this regular expression, or if it matches
comment-start-skip, then it is used—otherwise, spaces amounting to the same width are used instead.However, the fill prefix is never taken from a one-line paragraph if it would act as a paragraph starter on subsequent lines.
You can specify more complex ways of choosing a fill prefix automatically by setting this variable to a function. The function is called when
adaptive-fill-regexpdoes not match, with point after the left margin of a line, and it should return the appropriate fill prefix based on that line. If it returnsnil, that means it sees no fill prefix in that line.
Auto Fill mode is a minor mode that fills lines automatically as text is inserted. This section describes the hook used by Auto Fill mode. For a description of functions that you can call explicitly to fill and justify existing text, see Filling.
Auto Fill mode also enables the functions that change the margins and justification style to refill portions of the text. See Margins.
The value of this variable should be a function (of no arguments) to be called after self-inserting a character from the table
auto-fill-chars. It may benil, in which case nothing special is done in that case.The value of
auto-fill-functionisdo-auto-fillwhen Auto-Fill mode is enabled. That is a function whose sole purpose is to implement the usual strategy for breaking a line.In older Emacs versions, this variable was namedauto-fill-hook, but since it is not called with the standard convention for hooks, it was renamed toauto-fill-functionin version 19.
This variable specifies the function to use for
auto-fill-function, if and when Auto Fill is turned on. Major modes can set buffer-local values for this variable to alter how Auto Fill works.
A char table of characters which invoke
auto-fill-functionwhen self-inserted—space and newline in most language environments. They have an entrytin the table.
The sorting functions described in this section all rearrange text in
a buffer. This is in contrast to the function sort, which
rearranges the order of the elements of a list (see Rearrangement).
The values returned by these functions are not meaningful.
This function is the general text-sorting routine that subdivides a buffer into records and then sorts them. Most of the commands in this section use this function.
To understand how
sort-subrworks, consider the whole accessible portion of the buffer as being divided into disjoint pieces called sort records. The records may or may not be contiguous, but they must not overlap. A portion of each sort record (perhaps all of it) is designated as the sort key. Sorting rearranges the records in order by their sort keys.Usually, the records are rearranged in order of ascending sort key. If the first argument to the
sort-subrfunction, reverse, is non-nil, the sort records are rearranged in order of descending sort key.The next four arguments to
sort-subrare functions that are called to move point across a sort record. They are called many times from withinsort-subr.
- nextrecfun is called with point at the end of a record. This function moves point to the start of the next record. The first record is assumed to start at the position of point when
sort-subris called. Therefore, you should usually move point to the beginning of the buffer before callingsort-subr.This function can indicate there are no more sort records by leaving point at the end of the buffer.
- endrecfun is called with point within a record. It moves point to the end of the record.
- startkeyfun is called to move point from the start of a record to the start of the sort key. This argument is optional; if it is omitted, the whole record is the sort key. If supplied, the function should either return a non-
nilvalue to be used as the sort key, or returnnilto indicate that the sort key is in the buffer starting at point. In the latter case, endkeyfun is called to find the end of the sort key.- endkeyfun is called to move point from the start of the sort key to the end of the sort key. This argument is optional. If startkeyfun returns
niland this argument is omitted (ornil), then the sort key extends to the end of the record. There is no need for endkeyfun if startkeyfun returns a non-nilvalue.As an example of
sort-subr, here is the complete function definition forsort-lines:;; Note that the first two lines of doc string ;; are effectively one line when viewed by a user. (defun sort-lines (reverse beg end) "Sort lines in region alphabetically;\ argument means descending order. Called from a program, there are three arguments: REVERSE (non-nil means reverse order),\ BEG and END (region to sort). The variable `sort-fold-case' determines\ whether alphabetic case affects the sort order. (interactive "P\nr") (save-excursion (save-restriction (narrow-to-region beg end) (goto-char (point-min)) (sort-subr reverse 'forward-line 'end-of-line))))Here
forward-linemoves point to the start of the next record, andend-of-linemoves point to the end of record. We do not pass the arguments startkeyfun and endkeyfun, because the entire record is used as the sort key.The
sort-paragraphsfunction is very much the same, except that itssort-subrcall looks like this:(sort-subr reverse (function (lambda () (while (and (not (eobp)) (looking-at paragraph-separate)) (forward-line 1)))) 'forward-paragraph)Markers pointing into any sort records are left with no useful position after
sort-subrreturns.
If this variable is non-
nil,sort-subrand the other buffer sorting functions ignore case when comparing strings.
This command sorts the region between start and end alphabetically as specified by record-regexp and key-regexp. If reverse is a negative integer, then sorting is in reverse order.
Alphabetical sorting means that two sort keys are compared by comparing the first characters of each, the second characters of each, and so on. If a mismatch is found, it means that the sort keys are unequal; the sort key whose character is less at the point of first mismatch is the lesser sort key. The individual characters are compared according to their numerical character codes in the Emacs character set.
The value of the record-regexp argument specifies how to divide the buffer into sort records. At the end of each record, a search is done for this regular expression, and the text that matches it is taken as the next record. For example, the regular expression ‘^.+$’, which matches lines with at least one character besides a newline, would make each such line into a sort record. See Regular Expressions, for a description of the syntax and meaning of regular expressions.
The value of the key-regexp argument specifies what part of each record is the sort key. The key-regexp could match the whole record, or only a part. In the latter case, the rest of the record has no effect on the sorted order of records, but it is carried along when the record moves to its new position.
The key-regexp argument can refer to the text matched by a subexpression of record-regexp, or it can be a regular expression on its own.
If key-regexp is:
- ‘\digit’
- then the text matched by the digitth ‘\(...\)’ parenthesis grouping in record-regexp is the sort key.
- ‘\&’
- then the whole record is the sort key.
- a regular expression
- then
sort-regexp-fieldssearches for a match for the regular expression within the record. If such a match is found, it is the sort key. If there is no match for key-regexp within a record then that record is ignored, which means its position in the buffer is not changed. (The other records may move around it.)For example, if you plan to sort all the lines in the region by the first word on each line starting with the letter ‘f’, you should set record-regexp to ‘^.*$’ and set key-regexp to ‘\<f\w*\>’. The resulting expression looks like this:
(sort-regexp-fields nil "^.*$" "\\<f\\w*\\>" (region-beginning) (region-end))If you call
sort-regexp-fieldsinteractively, it prompts for record-regexp and key-regexp in the minibuffer.
This command alphabetically sorts lines in the region between start and end. If reverse is non-
nil, the sort is in reverse order.
This command alphabetically sorts paragraphs in the region between start and end. If reverse is non-
nil, the sort is in reverse order.
This command alphabetically sorts pages in the region between start and end. If reverse is non-
nil, the sort is in reverse order.
This command sorts lines in the region between start and end, comparing them alphabetically by the fieldth field of each line. Fields are separated by whitespace and numbered starting from 1. If field is negative, sorting is by the −fieldth field from the end of the line. This command is useful for sorting tables.
This command sorts lines in the region between start and end, comparing them numerically by the fieldth field of each line. The specified field must contain a number in each line of the region. Fields are separated by whitespace and numbered starting from 1. If field is negative, sorting is by the −fieldth field from the end of the line. This command is useful for sorting tables.
This command sorts the lines in the region between beg and end, comparing them alphabetically by a certain range of columns. The column positions of beg and end bound the range of columns to sort on.
If reverse is non-
nil, the sort is in reverse order.One unusual thing about this command is that the entire line containing position beg, and the entire line containing position end, are included in the region sorted.
Note that
sort-columnsuses thesortutility program, and so cannot work properly on text containing tab characters. Use M-x untabify to convert tabs to spaces before sorting.
The column functions convert between a character position (counting characters from the beginning of the buffer) and a column position (counting screen characters from the beginning of a line).
These functions count each character according to the number of
columns it occupies on the screen. This means control characters count
as occupying 2 or 4 columns, depending upon the value of
ctl-arrow, and tabs count as occupying a number of columns that
depends on the value of tab-width and on the column where the tab
begins. See Usual Display.
Column number computations ignore the width of the window and the amount of horizontal scrolling. Consequently, a column value can be arbitrarily high. The first (or leftmost) column is numbered 0.
This function returns the horizontal position of point, measured in columns, counting from 0 at the left margin. The column position is the sum of the widths of all the displayed representations of the characters between the start of the current line and point.
For an example of using
current-column, see the description ofcount-linesin Text Lines.
This function moves point to column in the current line. The calculation of column takes into account the widths of the displayed representations of the characters between the start of the line and point.
If column column is beyond the end of the line, point moves to the end of the line. If column is negative, point moves to the beginning of the line.
If it is impossible to move to column column because that is in the middle of a multicolumn character such as a tab, point moves to the end of that character. However, if force is non-
nil, and column is in the middle of a tab, thenmove-to-columnconverts the tab into spaces so that it can move precisely to column column. Other multicolumn characters can cause anomalies despite force, since there is no way to split them.The argument force also has an effect if the line isn't long enough to reach column column; if it is
t, that means to add whitespace at the end of the line to reach that column.If column is not an integer, an error is signaled.
The return value is the column number actually moved to.
The indentation functions are used to examine, move to, and change whitespace that is at the beginning of a line. Some of the functions can also change whitespace elsewhere on a line. Columns and indentation count from zero at the left margin.
This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives. See Width, for related functions.
This function returns the indentation of the current line, which is the horizontal position of the first nonblank character. If the contents are entirely blank, then this is the horizontal position of the end of the line.
This function indents from point with tabs and spaces until column is reached. If minimum is specified and non-
nil, then at least that many spaces are inserted even if this requires going beyond column. Otherwise the function does nothing if point is already beyond column. The value is the column at which the inserted indentation ends.The inserted whitespace characters inherit text properties from the surrounding text (usually, from the preceding text only). See Sticky Properties.
If this variable is non-
nil, indentation functions can insert tabs as well as spaces. Otherwise, they insert only spaces. Setting this variable automatically makes it buffer-local in the current buffer.
An important function of each major mode is to customize the <TAB> key to indent properly for the language being edited. This section describes the mechanism of the <TAB> key and how to control it. The functions in this section return unpredictable values.
This variable's value is the function to be used by <TAB> (and various commands) to indent the current line. The command
indent-according-to-modedoes no more than call this function.In Lisp mode, the value is the symbol
lisp-indent-line; in C mode,c-indent-line; in Fortran mode,fortran-indent-line. In Fundamental mode, Text mode, and many other modes with no standard for indentation, the value isindent-to-left-margin(which is the default value).
This command calls the function in
indent-line-functionto indent the current line in a way appropriate for the current major mode.
This command calls the function in
indent-line-functionto indent the current line; however, if that function isindent-to-left-margin,insert-tabis called instead. (That is a trivial command that inserts a tab character.)
This function inserts a newline, then indents the new line (the one following the newline just inserted) according to the major mode.
It does indentation by calling the current
indent-line-function. In programming language modes, this is the same thing <TAB> does, but in some text modes, where <TAB> inserts a tab,newline-and-indentindents to the column specified byleft-margin.
This command reindents the current line, inserts a newline at point, and then indents the new line (the one following the newline just inserted).
This command does indentation on both lines according to the current major mode, by calling the current value of
indent-line-function. In programming language modes, this is the same thing <TAB> does, but in some text modes, where <TAB> inserts a tab,reindent-then-newline-and-indentindents to the column specified byleft-margin.
This section describes commands that indent all the lines in the region. They return unpredictable values.
This command indents each nonblank line starting between start (inclusive) and end (exclusive). If to-column is
nil,indent-regionindents each nonblank line by calling the current mode's indentation function, the value ofindent-line-function.If to-column is non-
nil, it should be an integer specifying the number of columns of indentation; then this function gives each line exactly that much indentation, by either adding or deleting whitespace.If there is a fill prefix,
indent-regionindents each line by making it start with the fill prefix.
The value of this variable is a function that can be used by
indent-regionas a short cut. It should take two arguments, the start and end of the region. You should design the function so that it will produce the same results as indenting the lines of the region one by one, but presumably faster.If the value is
nil, there is no short cut, andindent-regionactually works line by line.A short-cut function is useful in modes such as C mode and Lisp mode, where the
indent-line-functionmust scan from the beginning of the function definition: applying it to each line would be quadratic in time. The short cut can update the scan information as it moves through the lines indenting them; this takes linear time. In a mode where indenting a line individually is fast, there is no need for a short cut.
indent-regionwith a non-nilargument to-column has a different meaning and does not use this variable.
This command indents all lines starting between start (inclusive) and end (exclusive) sideways by count columns. This “preserves the shape” of the affected region, moving it as a rigid unit. Consequently, this command is useful not only for indenting regions of unindented text, but also for indenting regions of formatted code.
For example, if count is 3, this command adds 3 columns of indentation to each of the lines beginning in the region specified.
In Mail mode, C-c C-y (
mail-yank-original) usesindent-rigidlyto indent the text copied from the message being replied to.
This is like
indent-rigidly, except that it doesn't alter lines that start within strings or comments.In addition, it doesn't alter a line if nochange-regexp matches at the beginning of the line (if nochange-regexp is non-
nil).
This section describes two commands that indent the current line based on the contents of previous lines.
This command inserts whitespace at point, extending to the same column as the next indent point of the previous nonblank line. An indent point is a non-whitespace character following whitespace. The next indent point is the first one at a column greater than the current column of point. For example, if point is underneath and to the left of the first non-blank character of a line of text, it moves to that column by inserting whitespace.
If the previous nonblank line has no next indent point (i.e., none at a great enough column position),
indent-relativeeither does nothing (if unindented-ok is non-nil) or callstab-to-tab-stop. Thus, if point is underneath and to the right of the last column of a short line of text, this command ordinarily moves point to the next tab stop by inserting whitespace.The return value of
indent-relativeis unpredictable.In the following example, point is at the beginning of the second line:
This line is indented twelve spaces. -!-The quick brown fox jumped.Evaluation of the expression
(indent-relative nil)produces the following:This line is indented twelve spaces. -!-The quick brown fox jumped.In this next example, point is between the ‘m’ and ‘p’ of ‘jumped’:
This line is indented twelve spaces. The quick brown fox jum-!-ped.Evaluation of the expression
(indent-relative nil)produces the following:This line is indented twelve spaces. The quick brown fox jum -!-ped.
This command indents the current line like the previous nonblank line, by calling
indent-relativewithtas the unindented-ok argument. The return value is unpredictable.If the previous nonblank line has no indent points beyond the current column, this command does nothing.
This section explains the mechanism for user-specified “tab stops” and the mechanisms that use and set them. The name “tab stops” is used because the feature is similar to that of the tab stops on a typewriter. The feature works by inserting an appropriate number of spaces and tab characters to reach the next tab stop column; it does not affect the display of tab characters in the buffer (see Usual Display). Note that the <TAB> character as input uses this tab stop feature only in a few major modes, such as Text mode.
This command inserts spaces or tabs before point, up to the next tab stop column defined by
tab-stop-list. It searches the list for an element greater than the current column number, and uses that element as the column to indent to. It does nothing if no such element is found.
This variable is the list of tab stop columns used by
tab-to-tab-stops. The elements should be integers in increasing order. The tab stop columns need not be evenly spaced.Use M-x edit-tab-stops to edit the location of tab stops interactively.
These commands, primarily for interactive use, act based on the indentation in the text.
This command moves point to the first non-whitespace character in the current line (which is the line in which point is located). It returns
nil.
This command moves point backward arg lines and then to the first nonblank character on that line. It returns
nil.
This command moves point forward arg lines and then to the first nonblank character on that line. It returns
nil.
The case change commands described here work on text in the current buffer. See Case Conversion, for case conversion functions that work on strings and characters. See Case Tables, for how to customize which characters are upper or lower case and how to convert them.
This function capitalizes all words in the region defined by start and end. To capitalize means to convert each word's first character to upper case and convert the rest of each word to lower case. The function returns
nil.If one end of the region is in the middle of a word, the part of the word within the region is treated as an entire word.
When
capitalize-regionis called interactively, start and end are point and the mark, with the smallest first.---------- Buffer: foo ---------- This is the contents of the 5th foo. ---------- Buffer: foo ---------- (capitalize-region 1 44) => nil ---------- Buffer: foo ---------- This Is The Contents Of The 5th Foo. ---------- Buffer: foo ----------
This function converts all of the letters in the region defined by start and end to lower case. The function returns
nil.When
downcase-regionis called interactively, start and end are point and the mark, with the smallest first.
This function converts all of the letters in the region defined by start and end to upper case. The function returns
nil.When
upcase-regionis called interactively, start and end are point and the mark, with the smallest first.
This function capitalizes count words after point, moving point over as it does. To capitalize means to convert each word's first character to upper case and convert the rest of each word to lower case. If count is negative, the function capitalizes the −count previous words but does not move point. The value is
nil.If point is in the middle of a word, the part of the word before point is ignored when moving forward. The rest is treated as an entire word.
When
capitalize-wordis called interactively, count is set to the numeric prefix argument.
This function converts the count words after point to all lower case, moving point over as it does. If count is negative, it converts the −count previous words but does not move point. The value is
nil.When
downcase-wordis called interactively, count is set to the numeric prefix argument.
This function converts the count words after point to all upper case, moving point over as it does. If count is negative, it converts the −count previous words but does not move point. The value is
nil.When
upcase-wordis called interactively, count is set to the numeric prefix argument.
Each character position in a buffer or a string can have a text property list, much like the property list of a symbol (see Property Lists). The properties belong to a particular character at a particular place, such as, the letter ‘T’ at the beginning of this sentence or the first ‘o’ in ‘foo’—if the same character occurs in two different places, the two occurrences generally have different properties.
Each property has a name and a value. Both of these can be any Lisp object, but the name is normally a symbol. The usual way to access the property list is to specify a name and ask what value corresponds to it.
If a character has a category property, we call it the
category of the character. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the character.
Copying text between strings and buffers preserves the properties
along with the characters; this includes such diverse functions as
substring, insert, and buffer-substring.
The simplest way to examine text properties is to ask for the value of
a particular property of a particular character. For that, use
get-text-property. Use text-properties-at to get the
entire property list of a character. See Property Search, for
functions to examine the properties of a number of characters at once.
These functions handle both strings and buffers. Keep in mind that positions in a string start from 0, whereas positions in a buffer start from 1.
This function returns the value of the prop property of the character after position pos in object (a buffer or string). The argument object is optional and defaults to the current buffer.
If there is no prop property strictly speaking, but the character has a category that is a symbol, then
get-text-propertyreturns the prop property of that symbol.
This function is like
get-text-property, except that it checks overlays first and then text properties. See Overlays.The argument object may be a string, a buffer, or a window. If it is a window, then the buffer displayed in that window is used for text properties and overlays, but only the overlays active for that window are considered. If object is a buffer, then all overlays in that buffer are considered, as well as text properties. If object is a string, only text properties are considered, since strings never have overlays.
This function returns the entire property list of the character at position in the string or buffer object. If object is
nil, it defaults to the current buffer.
This variable holds a property list giving default values for text properties. Whenever a character does not specify a value for a property, neither directly nor through a category symbol, the value stored in this list is used instead. Here is an example:
(setq default-text-properties '(foo 69)) ;; Make sure character 1 has no properties of its own. (set-text-properties 1 2 nil) ;; What we get, when we ask, is the default value. (get-text-property 1 'foo) => 69
The primitives for changing properties apply to a specified range of
text in a buffer or string. The function set-text-properties
(see end of section) sets the entire property list of the text in that
range; more often, it is useful to add, change, or delete just certain
properties specified by name.
Since text properties are considered part of the contents of the buffer (or string), and can affect how a buffer looks on the screen, any change in buffer text properties marks the buffer as modified. Buffer text property changes are undoable also (see Undo).
This function sets the prop property to value for the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.
This function adds or overrides text properties for the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.The argument props specifies which properties to add. It should have the form of a property list (see Property Lists): a list whose elements include the property names followed alternately by the corresponding values.
The return value is
tif the function actually changed some property's value;nilotherwise (if props isnilor its values agree with those in the text).For example, here is how to set the
commentandfaceproperties of a range of text:(add-text-properties start end '(comment t face highlight))
This function deletes specified text properties from the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.The argument props specifies which properties to delete. It should have the form of a property list (see Property Lists): a list whose elements are property names alternating with corresponding values. But only the names matter—the values that accompany them are ignored. For example, here's how to remove the
faceproperty.(remove-text-properties start end '(face nil))The return value is
tif the function actually changed some property's value;nilotherwise (if props isnilor if no character in the specified text had any of those properties).To remove all text properties from certain text, use
set-text-propertiesand specifynilfor the new property list.
This function completely replaces the text property list for the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.The argument props is the new property list. It should be a list whose elements are property names alternating with corresponding values.
After
set-text-propertiesreturns, all the characters in the specified range have identical properties.If props is
nil, the effect is to get rid of all properties from the specified range of text. Here's an example:(set-text-properties start end nil)
The easiest way to make a string with text properties
is with propertize:
This function returns a copy of string which has the text properties properties. These properties apply to all the characters in the string that is returned. Here is an example that constructs a string with a
faceproperty and amouse-faceproperty:(propertize "foo" 'face 'italic 'mouse-face 'bold-italic) => #("foo" 0 3 (mouse-face bold-italic face italic))To put different properties on various parts of a string, you can construct each part with
propertizeand then combine them withconcat:(concat (propertize "foo" 'face 'italic 'mouse-face 'bold-italic) " and " (propertize "bar" 'face 'italic 'mouse-face 'bold-italic)) => #("foo and bar" 0 3 (face italic mouse-face bold-italic) 3 8 nil 8 11 (face italic mouse-face bold-italic))
See also the function buffer-substring-no-properties
(see Buffer Contents) which copies text from the buffer
but does not copy its properties.
In typical use of text properties, most of the time several or many consecutive characters have the same value for a property. Rather than writing your programs to examine characters one by one, it is much faster to process chunks of text that have the same property value.
Here are functions you can use to do this. They use eq for
comparing property values. In all cases, object defaults to the
current buffer.
For high performance, it's very important to use the limit argument to these functions, especially the ones that search for a single property—otherwise, they may spend a long time scanning to the end of the buffer, if the property you are interested in does not change.
These functions do not move point; instead, they return a position (or
nil). Remember that a position is always between two characters;
the position returned by these functions is between two characters with
different properties.
The function scans the text forward from position pos in the string or buffer object till it finds a change in some text property, then returns the position of the change. In other words, it returns the position of the first character beyond pos whose properties are not identical to those of the character just after pos.
If limit is non-
nil, then the scan ends at position limit. If there is no property change before that point,next-property-changereturns limit.The value is
nilif the properties remain unchanged all the way to the end of object and limit isnil. If the value is non-nil, it is a position greater than or equal to pos. The value equals pos only when limit equals pos.Here is an example of how to scan the buffer by chunks of text within which all properties are constant:
(while (not (eobp)) (let ((plist (text-properties-at (point))) (next-change (or (next-property-change (point) (current-buffer)) (point-max)))) Process text from point to next-change... (goto-char next-change)))
The function scans the text forward from position pos in the string or buffer object till it finds a change in the prop property, then returns the position of the change. In other words, it returns the position of the first character beyond pos whose prop property differs from that of the character just after pos.
If limit is non-
nil, then the scan ends at position limit. If there is no property change before that point,next-single-property-changereturns limit.The value is
nilif the property remains unchanged all the way to the end of object and limit isnil. If the value is non-nil, it is a position greater than or equal to pos; it equals pos only if limit equals pos.
This is like
next-property-change, but scans back from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.
This is like
next-single-property-change, but scans back from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.
This is like
next-property-changeexcept that it considers overlay properties as well as text properties, and if no change is found before the end of the buffer, it returns the maximum buffer position rather thannil(in this sense, it resembles the corresponding overlay functionnext-overlay-change, rather thannext-property-change). There is no object operand because this function operates only on the current buffer. It returns the next address at which either kind of property changes.
This is like
next-char-property-change, but scans back from pos instead of forward, and returns the minimum buffer position if no change is found.
This is like
next-single-property-changeexcept that it considers overlay properties as well as text properties, and if no change is found before the end of the object, it returns the maximum valid position in object rather thannil. Unlikenext-char-property-change, this function does have an object operand; if object is not a buffer, only text-properties are considered.
This is like
next-single-char-property-change, but scans back from pos instead of forward, and returns the minimum valid position in object if no change is found.
This function returns non-
nilif at least one character between start and end has a property prop whose value is value. More precisely, it returns the position of the first such character. Otherwise, it returnsnil.The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.
This function returns non-
nilif at least one character between start and end does not have a property prop with value value. More precisely, it returns the position of the first such character. Otherwise, it returnsnil.The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.
Here is a table of text property names that have special built-in meanings. The following sections list a few additional special property names that control filling and property inheritance. All other names have no standard meaning, and you can use them as you like.
categorycategory property, we call it the
category of the character. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the character.
faceface to control the font and color of
text. See Faces, for more information.
In the simplest case, the value is a face name. It can also be a list; then each element can be any of these possibilities;
(foreground-color . color-name) or
(background-color . color-name). These elements specify
just the foreground color or just the background color.
(foreground-color . color-name) is equivalent to
(:foreground color-name), and likewise for the background.
See Font Lock Mode, for information on how to update face
properties automatically based on the contents of the text.
mouse-facemouse-face is used instead of face when the
mouse is on or near the character. For this purpose, “near” means
that all text between the character and where the mouse is have the same
mouse-face property value.
fontifiednil, says that text in the buffer has
had faces assigned automatically by a feature such as Font-Lock mode.
See Auto Faces.
displayhelp-echohelp-echo property, then when you
move the mouse onto that text, Emacs displays that string in the echo
area, or in the tooltip window.
If the value of the help-echo property is a function, that
function is called with three arguments, window, object and
position and should return a help string or nil for
none. The first argument, window is the window in which
the help was found. The second, object, is the buffer, overlay or
string which had the help-echo property. The position
argument is as follows:
help-echo text property was found.
help-echo
property, and pos is the position in the overlay's buffer under
the mouse.
display property), pos is the position in that
string under the mouse.
If the value of the help-echo property is neither a function nor
a string, it is evaluated to obtain a help string.
You can alter the way help text is displayed by setting the variable
show-help-function (see Help display).
This feature is used in the mode line and for other active text. It is
available starting in Emacs 21.
local-maplocal-map property. The property's value for the
character after point, if non-nil, is used for key lookup instead
of the buffer's local map. If the property value is a symbol, the
symbol's function definition is used as the keymap. See Active Keymaps.
keymapkeymap property is similar to local-map but overrides the
buffer's local map (and the map specified by the local-map
property) rather than replacing it.
syntax-tablesyntax-table property overrides what the syntax table says
about this particular character. See Syntax Properties.
read-onlyread-only, then modifying that
character is not allowed. Any command that would do so gets an error,
text-read-only.
Insertion next to a read-only character is an error if inserting
ordinary text there would inherit the read-only property due to
stickiness. Thus, you can control permission to insert next to
read-only text by controlling the stickiness. See Sticky Properties.
Since changing properties counts as modifying the buffer, it is not
possible to remove a read-only property unless you know the
special trick: bind inhibit-read-only to a non-nil value
and then remove the property. See Read Only Buffers.
invisiblenil invisible property can make a character invisible
on the screen. See Invisible Text, for details.
intangiblenil
intangible properties, then you cannot place point between them.
If you try to move point forward into the group, point actually moves to
the end of the group. If you try to move point backward into the group,
point actually moves to the start of the group.
When the variable inhibit-point-motion-hooks is non-nil,
the intangible property is ignored.
fieldfield property constitute a
field. Some motion functions including forward-word and
beginning-of-line stop moving at a field boundary.
See Fields.
modification-hooksmodification-hooks, then its
value should be a list of functions; modifying that character calls all
of those functions. Each function receives two arguments: the beginning
and end of the part of the buffer being modified. Note that if a
particular modification hook function appears on several characters
being modified by a single primitive, you can't predict how many times
the function will be called.
insert-in-front-hooksinsert-behind-hooksinsert-in-front-hooks property of the following
character and in the insert-behind-hooks property of the
preceding character. These functions receive two arguments, the
beginning and end of the inserted text. The functions are called
after the actual insertion takes place.
See also Change Hooks, for other hooks that are called
when you change text in a buffer.
point-enteredpoint-leftpoint-entered and point-left
record hook functions that report motion of point. Each time point
moves, Emacs compares these two property values:
point-left property of the character after the old location,
and
point-entered property of the character after the new
location.
If these two values differ, each of them is called (if not nil)
with two arguments: the old value of point, and the new one.
The same comparison is made for the characters before the old and new
locations. The result may be to execute two point-left functions
(which may be the same function) and/or two point-entered
functions (which may be the same function). In any case, all the
point-left functions are called first, followed by all the
point-entered functions.
It is possible using char-after to examine characters at various
positions without moving point to those positions. Only an actual
change in the value of point runs these hook functions.
When this variable is non-
nil,point-leftandpoint-enteredhooks are not run, and theintangibleproperty has no effect. Do not set this variable globally; bind it withlet.
If this variable is non-
nil, it specifies a function called to display help strings. These may behelp-echoproperties, menu help strings (see Simple Menu Items, see Extended Menu Items), or tool bar help strings (see Tool Bar). The specified function is called with one argument, the help string to display. Tooltip mode (see Tooltips) provides an example.
These text properties affect the behavior of the fill commands. They are used for representing formatted text. See Filling, and Margins.
harduse-hard-newlines is non-nil.
right-marginleft-marginjustificationSelf-inserting characters normally take on the same properties as the preceding character. This is called inheritance of properties.
In a Lisp program, you can do insertion with inheritance or without,
depending on your choice of insertion primitive. The ordinary text
insertion functions such as insert do not inherit any properties.
They insert text with precisely the properties of the string being
inserted, and no others. This is correct for programs that copy text
from one context to another—for example, into or out of the kill ring.
To insert with inheritance, use the special primitives described in this
section. Self-inserting characters inherit properties because they work
using these primitives.
When you do insertion with inheritance, which properties are inherited, and from where, depends on which properties are sticky. Insertion after a character inherits those of its properties that are rear-sticky. Insertion before a character inherits those of its properties that are front-sticky. When both sides offer different sticky values for the same property, the previous character's value takes precedence.
By default, a text property is rear-sticky but not front-sticky; thus, the default is to inherit all the properties of the preceding character, and nothing from the following character.
You can control the stickiness of various text properties with two
specific text properties, front-sticky and rear-nonsticky,
and with the variable text-property-default-nonsticky. You can
use the variable to specify a different default for a given property.
You can use those two text properties to make any specific properties
sticky or nonsticky in any particular part of the text.
If a character's front-sticky property is t, then all
its properties are front-sticky. If the front-sticky property is
a list, then the sticky properties of the character are those whose
names are in the list. For example, if a character has a
front-sticky property whose value is (face read-only),
then insertion before the character can inherit its face property
and its read-only property, but no others.
The rear-nonsticky property works the opposite way. Most
properties are rear-sticky by default, so the rear-nonsticky
property says which properties are not rear-sticky. If a
character's rear-nonsticky property is t, then none of its
properties are rear-sticky. If the rear-nonsticky property is a
list, properties are rear-sticky unless their names are in the
list.
This variable holds an alist which defines the default rear-stickiness of various text properties. Each element has the form
(property.nonstickiness), and it defines the stickiness of a particular text property, property.If nonstickiness is non-
nil, this means that the property property is rear-nonsticky by default. Since all properties are front-nonsticky by default, this makes property nonsticky in both directions by default.The text properties
front-stickyandrear-nonsticky, when used, take precedence over the default nonstickiness specifed intext-property-default-nonsticky.
Here are the functions that insert text with inheritance of properties:
Insert the strings strings, just like the function
insert, but inherit any sticky properties from the adjoining text.
Insert the strings strings, just like the function
insert-before-markers, but inherit any sticky properties from the adjoining text.
See Insertion, for the ordinary insertion functions which do not inherit.
You can save text properties in files (along with the text itself), and restore the same text properties when visiting or inserting the files, using these two hooks:
This variable's value is a list of functions for
write-regionto run to encode text properties in some fashion as annotations to the text being written in the file. See Writing to Files.Each function in the list is called with two arguments: the start and end of the region to be written. These functions should not alter the contents of the buffer. Instead, they should return lists indicating annotations to write in the file in addition to the text in the buffer.
Each function should return a list of elements of the form
(position.string), where position is an integer specifying the relative position within the text to be written, and string is the annotation to add there.Each list returned by one of these functions must be already sorted in increasing order by position. If there is more than one function,
write-regionmerges the lists destructively into one sorted list.When
write-regionactually writes the text from the buffer to the file, it intermixes the specified annotations at the corresponding positions. All this takes place without modifying the buffer.
This variable holds a list of functions for
insert-file-contentsto call after inserting a file's contents. These functions should scan the inserted text for annotations, and convert them to the text properties they stand for.Each function receives one argument, the length of the inserted text; point indicates the start of that text. The function should scan that text for annotations, delete them, and create the text properties that the annotations specify. The function should return the updated length of the inserted text, as it stands after those changes. The value returned by one function becomes the argument to the next function.
These functions should always return with point at the beginning of the inserted text.
The intended use of
after-insert-file-functionsis for converting some sort of textual annotations into actual text properties. But other uses may be possible.
We invite users to write Lisp programs to store and retrieve text properties in files, using these hooks, and thus to experiment with various data formats and find good ones. Eventually we hope users will produce good, general extensions we can install in Emacs.
We suggest not trying to handle arbitrary Lisp objects as text property names or values—because a program that general is probably difficult to write, and slow. Instead, choose a set of possible data types that are reasonably flexible, and not too hard to encode.
See Format Conversion, for a related feature.
Instead of computing text properties for all the text in the buffer, you can arrange to compute the text properties for parts of the text when and if something depends on them.
The primitive that extracts text from the buffer along with its
properties is buffer-substring. Before examining the properties,
this function runs the abnormal hook buffer-access-fontify-functions.
This variable holds a list of functions for computing text properties. Before
buffer-substringcopies the text and text properties for a portion of the buffer, it calls all the functions in this list. Each of the functions receives two arguments that specify the range of the buffer being accessed. (The buffer itself is always the current buffer.)
The function buffer-substring-no-properties does not call these
functions, since it ignores text properties anyway.
In order to prevent the hook functions from being called more than
once for the same part of the buffer, you can use the variable
buffer-access-fontified-property.
If this value's variable is non-
nil, it is a symbol which is used as a text property name. A non-nilvalue for that text property means, “the other text properties for this character have already been computed.”If all the characters in the range specified for
buffer-substringhave a non-nilvalue for this property,buffer-substringdoes not call thebuffer-access-fontify-functionsfunctions. It assumes these characters already have the right text properties, and just copies the properties they already have.The normal way to use this feature is that the
buffer-access-fontify-functionsfunctions add this property, as well as others, to the characters they operate on. That way, they avoid being called over and over for the same text.
There are two ways to set up clickable text in a buffer. There are typically two parts of this: to make the text highlight when the mouse is over it, and to make a mouse button do something when you click it on that part of the text.
Highlighting is done with the mouse-face text property.
Here is an example of how Dired does it:
(condition-case nil
(if (dired-move-to-filename)
(put-text-property (point)
(save-excursion
(dired-move-to-end-of-filename)
(point))
'mouse-face 'highlight))
(error nil))
The first two arguments to put-text-property specify the
beginning and end of the text.
The usual way to make the mouse do something when you click it
on this text is to define mouse-2 in the major mode's
keymap. The job of checking whether the click was on clickable text
is done by the command definition. Here is how Dired does it:
(defun dired-mouse-find-file-other-window (event)
"In dired, visit the file or directory name you click on."
(interactive "e")
(let (file)
(save-excursion
(set-buffer (window-buffer (posn-window (event-end event))))
(save-excursion
(goto-char (posn-point (event-end event)))
(setq file (dired-get-filename))))
(select-window (posn-window (event-end event)))
(find-file-other-window (file-name-sans-versions file t))))
The reason for the outer save-excursion construct is to avoid
changing the current buffer; the reason for the inner one is to avoid
permanently altering point in the buffer you click on. In this case,
Dired uses the function dired-get-filename to determine which
file to visit, based on the position found in the event.
Instead of defining a mouse command for the major mode, you can define
a key binding for the clickable text itself, using the keymap
text property:
(let ((map (make-sparse-keymap)))
(define-key map [mouse-2] 'operate-this-button)
(put-text-property (point)
(save-excursion
(dired-move-to-end-of-filename)
(point))
'keymap map))
This method makes it possible to define different commands for various clickable pieces of text. Also, the major mode definition (or the global definition) remains available for the rest of the text in the buffer.
A field is a range of consecutive characters in the buffer that are
identified by having the same value (comparing with eq) of the
field property (either a text-property or an overlay property).
This section describes special functions that are available for
operating on fields.
You specify a field with a buffer position, pos. We think of each field as containing a range of buffer positions, so the position you specify stands for the field containing that position.
When the characters before and after pos are part of the same
field, there is no doubt which field contains pos: the one those
characters both belong to. When pos is at a boundary between
fields, which field it belongs to depends on the stickiness of the
field properties of the two surrounding characters (see Sticky Properties). The field whose property would be inherited by text
inserted at pos is the field that contains pos.
There is an anomalous case where newly inserted text at pos
would not inherit the field property from either side. This
happens if the previous character's field property is not
rear-sticky, and the following character's field property is not
front-sticky. In this case, pos belongs to neither the preceding
field nor the following field; the field functions treat it as belonging
to an empty field whose beginning and end are both at pos.
In all of these functions, if pos is omitted or nil, the
value of point is used by default.
This function returns the beginning of the field specified by pos.
If pos is at the beginning of its field, and escape-from-edge is non-
nil, then the return value is always the beginning of the preceding field that ends at pos, regardless of the stickiness of thefieldproperties around pos.
This function returns the end of the field specified by pos.
If pos is at the end of its field, and escape-from-edge is non-
nil, then the return value is always the end of the following field that begins at pos, regardless of the stickiness of thefieldproperties around pos.
This function returns the contents of the field specified by pos, as a string.
This function returns the contents of the field specified by pos, as a string, discarding text properties.
This function deletes the text of the field specified by pos.
This function “constrains” new-pos to the field that old-pos belongs to—in other words, it returns the position closest to new-pos that is in the same field as old-pos.
If new-pos is
nil, thenconstrain-to-fielduses the value of point instead, and moves point to the resulting position.If old-pos is at the boundary of two fields, then the acceptable positions for new-pos depend on the value of the optional argument escape-from-edge. If escape-from-edge is
nil, then new-pos is constrained to the field that has the samefieldproperty (either a text-property or an overlay property) that new characters inserted at old-pos would get. (This depends on the stickiness of thefieldproperty for the characters before and after old-pos.) If escape-from-edge is non-nil, new-pos is constrained to the union of the two adjacent fields. Additionally, if two fields are separated by another field with the special valueboundary, then any point within this special field is also considered to be “on the boundary.”If the optional argument only-in-line is non-
nil, and constraining new-pos in the usual way would move it to a different line, new-pos is returned unconstrained. This used in commands that move by line, such asnext-lineandbeginning-of-line, so that they respect field boundaries only in the case where they can still move to the right line.If the optional argument inhibit-capture-property is non-
nil, and old-pos has a non-nilproperty of that name, then any field boundaries are ignored.You can cause
constrain-to-fieldto ignore all field boundaries (and so never constrain anything) by binding the variableinhibit-field-text-motionto a non-nil value.
Some editors that support adding attributes to text in the buffer do so by letting the user specify “intervals” within the text, and adding the properties to the intervals. Those editors permit the user or the programmer to determine where individual intervals start and end. We deliberately provided a different sort of interface in Emacs Lisp to avoid certain paradoxical behavior associated with text modification.
If the actual subdivision into intervals is meaningful, that means you can distinguish between a buffer that is just one interval with a certain property, and a buffer containing the same text subdivided into two intervals, both of which have that property.
Suppose you take the buffer with just one interval and kill part of the text. The text remaining in the buffer is one interval, and the copy in the kill ring (and the undo list) becomes a separate interval. Then if you yank back the killed text, you get two intervals with the same properties. Thus, editing does not preserve the distinction between one interval and two.
Suppose we “fix” this problem by coalescing the two intervals when the text is inserted. That works fine if the buffer originally was a single interval. But suppose instead that we have two adjacent intervals with the same properties, and we kill the text of one interval and yank it back. The same interval-coalescence feature that rescues the other case causes trouble in this one: after yanking, we have just one interval. One again, editing does not preserve the distinction between one interval and two.
Insertion of text at the border between intervals also raises questions that have no satisfactory answer.
However, it is easy to arrange for editing to behave consistently for questions of the form, “What are the properties of this character?” So we have decided these are the only questions that make sense; we have not implemented asking questions about where intervals start or end.
In practice, you can usually use the text property search functions in place of explicit interval boundaries. You can think of them as finding the boundaries of intervals, assuming that intervals are always coalesced whenever possible. See Property Search.
Emacs also provides explicit intervals as a presentation feature; see Overlays.
The following functions replace characters within a specified region based on their character codes.
This function replaces all occurrences of the character old-char with the character new-char in the region of the current buffer defined by start and end.
If noundo is non-
nil, thensubst-char-in-regiondoes not record the change for undo and does not mark the buffer as modified. This was useful for controlling the old selective display feature (see Selective Display).
subst-char-in-regiondoes not move point and returnsnil.---------- Buffer: foo ---------- This is the contents of the buffer before. ---------- Buffer: foo ---------- (subst-char-in-region 1 20 ?i ?X) => nil ---------- Buffer: foo ---------- ThXs Xs the contents of the buffer before. ---------- Buffer: foo ----------
This function applies a translation table to the characters in the buffer between positions start and end.
The translation table table is a string;
(areftable ochar)gives the translated character corresponding to ochar. If the length of table is less than 256, any characters with codes larger than the length of table are not altered by the translation.The return value of
translate-regionis the number of characters that were actually changed by the translation. This does not count characters that were mapped into themselves in the translation table.
A register is a sort of variable used in Emacs editing that can hold a variety of different kinds of values. Each register is named by a single character. All ascii characters and their meta variants (but with the exception of C-g) can be used to name registers. Thus, there are 255 possible registers. A register is designated in Emacs Lisp by the character that is its name.
This variable is an alist of elements of the form
(name.contents). Normally, there is one element for each Emacs register that has been used.The object name is a character (an integer) identifying the register.
The contents of a register can have several possible types:
insert-register finds a number
in the register, it converts the number to decimal.
(window-configuration position)(frame-configuration position)The functions in this section return unpredictable values unless otherwise stated.
This function returns the contents of the register reg, or
nilif it has no contents.
This function sets the contents of register reg to value. A register can be set to any value, but the other register functions expect only certain data types. The return value is value.
This command inserts contents of register reg into the current buffer.
Normally, this command puts point before the inserted text, and the mark after it. However, if the optional second argument beforep is non-
nil, it puts the mark before and point after. You can pass a non-nilsecond argument beforep to this function interactively by supplying any prefix argument.If the register contains a rectangle, then the rectangle is inserted with its upper left corner at point. This means that text is inserted in the current line and underneath it on successive lines.
If the register contains something other than saved text (a string) or a rectangle (a list), currently useless things happen. This may be changed in the future.
This subroutine is used by the transposition commands.
This function exchanges two nonoverlapping portions of the buffer. Arguments start1 and end1 specify the bounds of one portion and arguments start2 and end2 specify the bounds of the other portion.
Normally,
transpose-regionsrelocates markers with the transposed text; a marker previously positioned within one of the two transposed portions moves along with that portion, thus remaining between the same two characters in their new position. However, if leave-markers is non-nil,transpose-regionsdoes not do this—it leaves all markers unrelocated.
Base 64 code is used in email to encode a sequence of 8-bit bytes as a longer sequence of ascii graphic characters. It is defined in Internet RFC72045. This section describes the functions for converting to and from this code.
This function converts the region from beg to end into base 64 code. It returns the length of the encoded text. An error is signaled if a character in the region is multibyte, i.e. in a multibyte buffer the region must contain only characters from the charsets
ascii,eight-bit-controlandeight-bit-graphic.Normally, this function inserts newline characters into the encoded text, to avoid overlong lines. However, if the optional argument no-line-break is non-
nil, these newlines are not added, so the output is just one long line.
This function converts the string string into base 64 code. It returns a string containing the encoded text. As for
base64-encode-region, an error is signaled if a character in the string is multibyte.Normally, this function inserts newline characters into the encoded text, to avoid overlong lines. However, if the optional argument no-line-break is non-
nil, these newlines are not added, so the result string is just one long line.
This function converts the region from beg to end from base 64 code into the corresponding decoded text. It returns the length of the decoded text.
The decoding functions ignore newline characters in the encoded text.
This function converts the string string from base 64 code into the corresponding decoded text. It returns a string containing the decoded text.
The decoding functions ignore newline characters in the encoded text.
MD5 cryptographic checksums, or message digests, are 128-bit “fingerprints” of a document or program. They are used to verify that you have an exact and unaltered copy of the data. The algorithm to calculate the MD5 message digest is defined in Internet RFC81321. This section describes the Emacs facilities for computing message digests.
This function returns the MD5 message digest of object, which should be a buffer or a string.
The two optional arguments start and end are character positions specifying the portion of object to compute the message digest for. If they are
nilor omitted, the digest is computed for the whole of object.The function
md5does not compute the message digest directly from the internal Emacs representation of the text (see Text Representations). Instead, it encodes the text using a coding system, and computes the message digest from the encoded text. The optional fourth argument coding-system specifies which coding system to use for encoding the text. It should be the same coding system that you used to read the text, or that you used or will use when saving or sending the text. See Coding Systems, for more information about coding systems.If coding-system is
nilor omitted, the default depends on object. If object is a buffer, the default for coding-system is whatever coding system would be chosen by default for writing this text into a file. If object is a string, the user's most preferred coding system (see prefer-coding-system) is used.Normally,
md5signals an error if the text can't be encoded using the specified or chosen coding system. However, if noerror is non-nil, it silently usesraw-textcoding instead.
These hook variables let you arrange to take notice of all changes in all buffers (or in a particular buffer, if you make them buffer-local). See also Special Properties, for how to detect changes to specific parts of the text.
The functions you use in these hooks should save and restore the match data if they do anything that uses regular expressions; otherwise, they will interfere in bizarre ways with the editing operations that call them.
This variable holds a list of functions to call before any buffer modification. Each function gets two arguments, the beginning and end of the region that is about to change, represented as integers. The buffer that is about to change is always the current buffer.
This variable holds a list of functions to call after any buffer modification. Each function receives three arguments: the beginning and end of the region just changed, and the length of the text that existed before the change. All three arguments are integers. The buffer that's about to change is always the current buffer.
The length of the old text is the difference between the buffer positions before and after that text as it was before the change. As for the changed text, its length is simply the difference between the first two arguments.
The macro executes body normally, but arranges to call the after-change functions just once for a series of several changes—if that seems safe.
If a program makes several text changes in the same area of the buffer, using the macro
combine-after-change-callsaround that part of the program can make it run considerably faster when after-change hooks are in use. When the after-change hooks are ultimately called, the arguments specify a portion of the buffer including all of the changes made within thecombine-after-change-callsbody.Warning: You must not alter the values of
after-change-functionswithin the body of acombine-after-change-callsform.Note: If the changes you combine occur in widely scattered parts of the buffer, this will still work, but it is not advisable, because it may lead to inefficient behavior for some change hook functions.
The two variables above are temporarily bound to nil during the
time that any of these functions is running. This means that if one of
these functions changes the buffer, that change won't run these
functions. If you do want a hook function to make changes that run
these functions, make it bind these variables back to their usual
values.
One inconvenient result of this protective feature is that you cannot
have a function in after-change-functions or
before-change-functions which changes the value of that variable.
But that's not a real limitation. If you want those functions to change
the list of functions to run, simply add one fixed function to the hook,
and code that function to look in another variable for other functions
to call. Here is an example:
(setq my-own-after-change-functions nil)
(defun indirect-after-change-function (beg end len)
(let ((list my-own-after-change-functions))
(while list
(funcall (car list) beg end len)
(setq list (cdr list)))))
(add-hooks 'after-change-functions
'indirect-after-change-function)
This variable is a normal hook that is run whenever a buffer is changed that was previously in the unmodified state.
If this variable is non-
nil, all of the change hooks are disabled; none of them run. This affects all the hook variables described above in this section, as well as the hooks attached to certain special text properties (see Special Properties) and overlay properties (see Overlay Properties).This variable is available starting in Emacs 21.
This chapter covers the special issues relating to non-ascii characters and how they are stored in strings and buffers.
Emacs has two text representations—two ways to represent text in a string or buffer. These are called unibyte and multibyte. Each string, and each buffer, uses one of these two representations. For most purposes, you can ignore the issue of representations, because Emacs converts text between them as appropriate. Occasionally in Lisp programming you will need to pay attention to the difference.
In unibyte representation, each character occupies one byte and
therefore the possible character codes range from 0 to 255. Codes 0
through 127 are ascii characters; the codes from 128 through 255
are used for one non-ascii character set (you can choose which
character set by setting the variable nonascii-insert-offset).
In multibyte representation, a character may occupy more than one byte, and as a result, the full range of Emacs character codes can be stored. The first byte of a multibyte character is always in the range 128 through 159 (octal 0200 through 0237). These values are called leading codes. The second and subsequent bytes of a multibyte character are always in the range 160 through 255 (octal 0240 through 0377); these values are trailing codes.
Some sequences of bytes are not valid in multibyte text: for example, a single isolated byte in the range 128 through 159 is not allowed. But character codes 128 through 159 can appear in multibyte text, represented as two-byte sequences. All the character codes 128 through 255 are possible (though slightly abnormal) in multibyte text; they appear in multibyte buffers and strings when you do explicit encoding and decoding (see Explicit Encoding).
In a buffer, the buffer-local value of the variable
enable-multibyte-characters specifies the representation used.
The representation for a string is determined and recorded in the string
when the string is constructed.
This variable specifies the current buffer's text representation. If it is non-
nil, the buffer contains multibyte text; otherwise, it contains unibyte text.You cannot set this variable directly; instead, use the function
set-buffer-multibyteto change a buffer's representation.
This variable's value is entirely equivalent to
(default-value 'enable-multibyte-characters), and setting this variable changes that default value. Setting the local binding ofenable-multibyte-charactersin a specific buffer is not allowed, but changing the default value is supported, and it is a reasonable thing to do, because it has no effect on existing buffers.The ‘--unibyte’ command line option does its job by setting the default value to
nilearly in startup.
Return the byte-position corresponding to buffer position position in the current buffer.
Return the buffer position corresponding to byte-position byte-position in the current buffer.
Emacs can convert unibyte text to multibyte; it can also convert multibyte text to unibyte, though this conversion loses information. In general these conversions happen when inserting text into a buffer, or when putting text from several strings together in one string. You can also explicitly convert a string's contents to either representation.
Emacs chooses the representation for a string based on the text that it is constructed from. The general rule is to convert unibyte text to multibyte text when combining it with other multibyte text, because the multibyte representation is more general and can hold whatever characters the unibyte text has.
When inserting text into a buffer, Emacs converts the text to the
buffer's representation, as specified by
enable-multibyte-characters in that buffer. In particular, when
you insert multibyte text into a unibyte buffer, Emacs converts the text
to unibyte, even though this conversion cannot in general preserve all
the characters that might be in the multibyte text. The other natural
alternative, to convert the buffer contents to multibyte, is not
acceptable because the buffer's representation is a choice made by the
user that cannot be overridden automatically.
Converting unibyte text to multibyte text leaves ascii characters
unchanged, and likewise character codes 128 through 159. It converts
the non-ascii codes 160 through 255 by adding the value
nonascii-insert-offset to each character code. By setting this
variable, you specify which character set the unibyte characters
correspond to (see Character Sets). For example, if
nonascii-insert-offset is 2048, which is (- (make-char
'latin-iso8859-1) 128), then the unibyte non-ascii characters
correspond to Latin 1. If it is 2688, which is (- (make-char
'greek-iso8859-7) 128), then they correspond to Greek letters.
Converting multibyte text to unibyte is simpler: it discards all but
the low 8 bits of each character code. If nonascii-insert-offset
has a reasonable value, corresponding to the beginning of some character
set, this conversion is the inverse of the other: converting unibyte
text to multibyte and back to unibyte reproduces the original unibyte
text.
This variable specifies the amount to add to a non-ascii character when converting unibyte text to multibyte. It also applies when
self-insert-commandinserts a character in the unibyte non-ascii range, 128 through 255. However, the functionsinsertandinsert-chardo not perform this conversion.The right value to use to select character set cs is
(- (make-charcs) 128). If the value ofnonascii-insert-offsetis zero, then conversion actually uses the value for the Latin 1 character set, rather than zero.
This variable provides a more general alternative to
nonascii-insert-offset. You can use it to specify independently how to translate each code in the range of 128 through 255 into a multibyte character. The value should be a char-table, ornil. If this is non-nil, it overridesnonascii-insert-offset.
This function converts the text of string to unibyte representation, if it isn't already, and returns the result. If string is a unibyte string, it is returned unchanged. Multibyte character codes are converted to unibyte by using just the low 8 bits.
This function converts the text of string to multibyte representation, if it isn't already, and returns the result. If string is a multibyte string, it is returned unchanged. The function
unibyte-char-to-multibyteis used to convert each unibyte character to a multibyte character.
Sometimes it is useful to examine an existing buffer or string as multibyte when it was unibyte, or vice versa.
Set the representation type of the current buffer. If multibyte is non-
nil, the buffer becomes multibyte. If multibyte isnil, the buffer becomes unibyte.This function leaves the buffer contents unchanged when viewed as a sequence of bytes. As a consequence, it can change the contents viewed as characters; a sequence of two bytes which is treated as one character in multibyte representation will count as two characters in unibyte representation. Character codes 128 through 159 are an exception. They are represented by one byte in a unibyte buffer, but when the buffer is set to multibyte, they are converted to two-byte sequences, and vice versa.
This function sets
enable-multibyte-charactersto record which representation is in use. It also adjusts various data in the buffer (including overlays, text properties and markers) so that they cover the same text as they did before.You cannot use
set-buffer-multibyteon an indirect buffer, because indirect buffers always inherit the representation of the base buffer.
This function returns a string with the same bytes as string but treating each byte as a character. This means that the value may have more characters than string has.
If string is already a unibyte string, then the value is string itself. Otherwise it is a newly created string, with no text properties. If string is multibyte, any characters it contains of charset eight-bit-control or eight-bit-graphic are converted to the corresponding single byte.
This function returns a string with the same bytes as string but treating each multibyte sequence as one character. This means that the value may have fewer characters than string has.
If string is already a multibyte string, then the value is string itself. Otherwise it is a newly created string, with no text properties. If string is unibyte and contains any individual 8-bit bytes (i.e. not part of a multibyte form), they are converted to the corresponding multibyte character of charset eight-bit-control or eight-bit-graphic.
The unibyte and multibyte text representations use different character codes. The valid character codes for unibyte representation range from 0 to 255—the values that can fit in one byte. The valid character codes for multibyte representation range from 0 to 524287, but not all values in that range are valid. The values 128 through 255 are not entirely proper in multibyte text, but they can occur if you do explicit encoding and decoding (see Explicit Encoding). Some other character codes cannot occur at all in multibyte text. Only the ascii codes 0 through 127 are completely legitimate in both representations.
This returns
tif charcode is valid for either one of the two text representations.(char-valid-p 65) => t (char-valid-p 256) => nil (char-valid-p 2248) => tIf the optional argument genericp is non-nil, this function returns
tif charcode is a generic character (see Splitting Characters).
Emacs classifies characters into various character sets, each of which has a name which is a symbol. Each character belongs to one and only one character set.
In general, there is one character set for each distinct script. For
example, latin-iso8859-1 is one character set,
greek-iso8859-7 is another, and ascii is another. An
Emacs character set can hold at most 9025 characters; therefore, in some
cases, characters that would logically be grouped together are split
into several character sets. For example, one set of Chinese
characters, generally known as Big 5, is divided into two Emacs
character sets, chinese-big5-1 and chinese-big5-2.
ascii characters are in character set ascii. The
non-ascii characters 128 through 159 are in character set
eight-bit-control, and codes 160 through 255 are in character set
eight-bit-graphic.
Returns
tif object is a symbol that names a character set,nilotherwise.
This function returns the name of the character set that character belongs to.
This function returns the charset property list of the character set charset. Although charset is a symbol, this is not the same as the property list of that symbol. Charset properties are used for special purposes within Emacs; for example,
preferred-coding-systemhelps determine which coding system to use to encode characters in a charset.
In multibyte representation, each character occupies one or more bytes. Each character set has an introduction sequence, which is normally one or two bytes long. (Exception: the ascii character set and the eight-bit-graphic character set have a zero-length introduction sequence.) The introduction sequence is the beginning of the byte sequence for any character in the character set. The rest of the character's bytes distinguish it from the other characters in the same character set. Depending on the character set, there are either one or two distinguishing bytes; the number of such bytes is called the dimension of the character set.
This function returns the dimension of charset; at present, the dimension is always 1 or 2.
This function returns the number of bytes used to represent a character in character set charset.
This is the simplest way to determine the byte length of a character set's introduction sequence:
(- (charset-bytes charset)
(charset-dimension charset))
The functions in this section convert between characters and the byte values used to represent them. For most purposes, there is no need to be concerned with the sequence of bytes used to represent a character, because Emacs translates automatically when necessary.
Return a list containing the name of the character set of character, followed by one or two byte values (integers) which identify character within that character set. The number of byte values is the character set's dimension.
(split-char 2248) => (latin-iso8859-1 72) (split-char 65) => (ascii 65) (split-char 128) => (eight-bit-control 128)
This function returns the character in character set charset whose position codes are code1 and code2. This is roughly the inverse of
split-char. Normally, you should specify either one or both of code1 and code2 according to the dimension of charset. For example,(make-char 'latin-iso8859-1 72) => 2248
If you call make-char with no byte-values, the result is
a generic character which stands for charset. A generic
character is an integer, but it is not valid for insertion in the
buffer as a character. It can be used in char-table-range to
refer to the whole character set (see Char-Tables).
char-valid-p returns nil for generic characters.
For example:
(make-char 'latin-iso8859-1)
=> 2176
(char-valid-p 2176)
=> nil
(char-valid-p 2176 t)
=> t
(split-char 2176)
=> (latin-iso8859-1 0)
The character sets ascii, eight-bit-control, and
eight-bit-graphic don't have corresponding generic characters. If
charset is one of them and you don't supply code1,
make-char returns the character code corresponding to the
smallest code in charset.
Sometimes it is useful to find out which character sets appear in a part of a buffer or a string. One use for this is in determining which coding systems (see Coding Systems) are capable of representing all of the text in question.
This function returns a list of the character sets that appear in the current buffer between positions beg and end.
The optional argument translation specifies a translation table to be used in scanning the text (see Translation of Characters). If it is non-
nil, then each character in the region is translated through this table, and the value returned describes the translated characters instead of the characters actually in the buffer.
This function returns a list of the character sets that appear in the string string. It is just like
find-charset-region, except that it applies to the contents of string instead of part of the current buffer.
A translation table specifies a mapping of characters into characters. These tables are used in encoding and decoding, and for other purposes. Some coding systems specify their own particular translation tables; there are also default translation tables which apply to all other coding systems.
This function returns a translation table based on the argument translations. Each element of translations should be a list of elements of the form
(from.to); this says to translate the character from into to.The arguments and the forms in each argument are processed in order, and if a previous form already translates to to some other character, say to-alt, from is also translated to to-alt.
You can also map one whole character set into another character set with the same dimension. To do this, you specify a generic character (which designates a character set) for from (see Splitting Characters). In this case, to should also be a generic character, for another character set of the same dimension. Then the translation table translates each character of from's character set into the corresponding character of to's character set.
In decoding, the translation table's translations are applied to the
characters that result from ordinary decoding. If a coding system has
property character-translation-table-for-decode, that specifies
the translation table to use. Otherwise, if
standard-translation-table-for-decode is non-nil, decoding
uses that table.
In encoding, the translation table's translations are applied to the
characters in the buffer, and the result of translation is actually
encoded. If a coding system has property
character-translation-table-for-encode, that specifies the
translation table to use. Otherwise the variable
standard-translation-table-for-encode specifies the translation
table.
This is the default translation table for decoding, for coding systems that don't specify any other translation table.
This is the default translation table for encoding, for coding systems that don't specify any other translation table.
When Emacs reads or writes a file, and when Emacs sends text to a subprocess or receives text from a subprocess, it normally performs character code conversion and end-of-line conversion as specified by a particular coding system.
How to define a coding system is an arcane matter, and is not documented here.
Character code conversion involves conversion between the encoding used inside Emacs and some other encoding. Emacs supports many different encodings, in that it can convert to and from them. For example, it can convert text to or from encodings such as Latin 1, Latin 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some cases, Emacs supports several alternative encodings for the same characters; for example, there are three coding systems for the Cyrillic (Russian) alphabet: ISO, Alternativnyj, and KOI8.
Most coding systems specify a particular character code for conversion, but some of them leave the choice unspecified—to be chosen heuristically for each file, based on the data.
End of line conversion handles three different conventions used on various systems for representing end of line in files. The Unix convention is to use the linefeed character (also called newline). The DOS convention is to use a carriage-return and a linefeed at the end of a line. The Mac convention is to use just carriage-return.
Base coding systems such as latin-1 leave the end-of-line
conversion unspecified, to be chosen based on the data. Variant
coding systems such as latin-1-unix, latin-1-dos and
latin-1-mac specify the end-of-line conversion explicitly as
well. Most base coding systems have three corresponding variants whose
names are formed by adding ‘-unix’, ‘-dos’ and ‘-mac’.
The coding system raw-text is special in that it prevents
character code conversion, and causes the buffer visited with that
coding system to be a unibyte buffer. It does not specify the
end-of-line conversion, allowing that to be determined as usual by the
data, and has the usual three variants which specify the end-of-line
conversion. no-conversion is equivalent to raw-text-unix:
it specifies no conversion of either character codes or end-of-line.
The coding system emacs-mule specifies that the data is
represented in the internal Emacs encoding. This is like
raw-text in that no code conversion happens, but different in
that the result is multibyte data.
This function returns the specified property of the coding system coding-system. Most coding system properties exist for internal purposes, but one that you might find useful is
mime-charset. That property's value is the name used in MIME for the character coding which this coding system can read and write. Examples:(coding-system-get 'iso-latin-1 'mime-charset) => iso-8859-1 (coding-system-get 'iso-2022-cn 'mime-charset) => iso-2022-cn (coding-system-get 'cyrillic-koi8 'mime-charset) => koi8-rThe value of the
mime-charsetproperty is also defined as an alias for the coding system.
The principal purpose of coding systems is for use in reading and
writing files. The function insert-file-contents uses
a coding system for decoding the file data, and write-region
uses one to encode the buffer contents.
You can specify the coding system to use either explicitly
(see Specifying Coding Systems), or implicitly using the defaulting
mechanism (see Default Coding Systems). But these methods may not
completely specify what to do. For example, they may choose a coding
system such as undefined which leaves the character code
conversion to be determined from the data. In these cases, the I/O
operation finishes the job of choosing a coding system. Very often
you will want to find out afterwards which coding system was chosen.
This variable records the coding system that was used for visiting the current buffer. It is used for saving the buffer, and for writing part of the buffer with
write-region. When those operations ask the user to specify a different coding system,buffer-file-coding-systemis updated to the coding system specified.However,
buffer-file-coding-systemdoes not affect sending text to a subprocess.
This variable specifies the coding system for saving the buffer (by overriding
buffer-file-coding-system). Note that it is not used forwrite-region.When a command to save the buffer starts out to use
buffer-file-coding-system(orsave-buffer-coding-system), and that coding system cannot handle the actual text in the buffer, the command asks the user to choose another coding system. After that happens, the command also updatesbuffer-file-coding-systemto represent the coding system that the user specified.
I/O operations for files and subprocesses set this variable to the coding system name that was used. The explicit encoding and decoding functions (see Explicit Encoding) set it too.
Warning: Since receiving subprocess output sets this variable, it can change whenever Emacs waits; therefore, you should copy the value shortly after the function call that stores the value you are interested in.
The variable selection-coding-system specifies how to encode
selections for the window system. See Window System Selections.
Here are the Lisp facilities for working with coding systems:
This function returns a list of all coding system names (symbols). If base-only is non-
nil, the value includes only the base coding systems. Otherwise, it includes alias and variant coding systems as well.
This function checks the validity of coding-system. If that is valid, it returns coding-system. Otherwise it signals an error with condition
coding-system-error.
This function returns a coding system which is like coding-system except for its eol conversion, which is specified by
eol-type. eol-type should beunix,dos,mac, ornil. If it isnil, the returned coding system determines the end-of-line conversion from the data.
This function returns a coding system which uses the end-of-line conversion of eol-coding, and the text conversion of text-coding. If text-coding is
nil, it returnsundecided, or one of its variants according to eol-coding.
This function returns a list of coding systems that could be used to encode a text between from and to. All coding systems in the list can safely encode any multibyte characters in that portion of the text.
If the text contains no multibyte characters, the function returns the list
(undecided).
This function returns a list of coding systems that could be used to encode the text of string. All coding systems in the list can safely encode any multibyte characters in string. If the text contains no multibyte characters, this returns the list
(undecided).
This function returns a list of coding systems that could be used to encode all the character sets in the list charsets.
This function chooses a plausible coding system for decoding the text from start to end. This text should be a byte sequence (see Explicit Encoding).
Normally this function returns a list of coding systems that could handle decoding the text that was scanned. They are listed in order of decreasing priority. But if highest is non-
nil, then the return value is just one coding system, the one that is highest in priority.If the region contains only ascii characters, the value is
undecidedor(undecided).
This function is like
detect-coding-regionexcept that it operates on the contents of string instead of bytes in the buffer.
See Process Information, for how to examine or set the coding systems used for I/O to a subprocess.
This function selects a coding system for encoding specified text, asking the user to choose if necessary. Normally the specified text is the text in the current buffer between from and to, defaulting to the whole buffer if they are
nil. If from is a string, the string is the specified text, and to is ignored.If default-coding-system is non-
nil, that is the first coding system to try; if that can handle the text,select-safe-coding-systemreturns that coding system. It can also be a list of coding systems; then the function tries each of them one by one. After trying all of them, it next tries the user's most preferred coding system (see prefer-coding-system), and after that the current buffer's value ofbuffer-file-coding-system(if it is notundecided).If one of those coding systems can safely encode all the specified text,
select-safe-coding-systemchooses it and returns it. Otherwise, it asks the user to choose from a list of coding systems which can encode all the text, and returns the user's choice.The optional argument accept-default-p, if non-
nil, should be a function to determine whether the coding system selected without user interaction is acceptable. If this function returnsnil, the silently selected coding system is rejected, and the user is asked to select a coding system from a list of possible candidates.If the variable
select-safe-coding-system-accept-default-pis non-nil, its value overrides the value of accept-default-p.
Here are two functions you can use to let the user specify a coding system, with completion. See Completion.
This function reads a coding system using the minibuffer, prompting with string prompt, and returns the coding system name as a symbol. If the user enters null input, default specifies which coding system to return. It should be a symbol or a string.
This function reads a coding system using the minibuffer, prompting with string prompt, and returns the coding system name as a symbol. If the user tries to enter null input, it asks the user to try again. See Coding Systems.
This section describes variables that specify the default coding system for certain files or when running certain subprograms, and the function that I/O operations use to access them.
The idea of these variables is that you set them once and for all to the
defaults you want, and then do not change them again. To specify a
particular coding system for a particular operation in a Lisp program,
don't change these variables; instead, override them using
coding-system-for-read and coding-system-for-write
(see Specifying Coding Systems).
This variable is an alist of text patterns and corresponding coding systems. Each element has the form
(regexp.coding-system); a file whose first few kilobytes match regexp is decoded with coding-system when its contents are read into a buffer. The settings in this alist take priority overcoding:tags in the files and the contents offile-coding-system-alist(see below). The default value is set so that Emacs automatically recognizes mail files in Babyl format and reads them with no code conversions.
This variable is an alist that specifies the coding systems to use for reading and writing particular files. Each element has the form
(pattern.coding), where pattern is a regular expression that matches certain file names. The element applies to file names that match pattern.The cdr of the element, coding, should be either a coding system, a cons cell containing two coding systems, or a function name (a symbol with a function definition). If coding is a coding system, that coding system is used for both reading the file and writing it. If coding is a cons cell containing two coding systems, its car specifies the coding system for decoding, and its cdr specifies the coding system for encoding.
If coding is a function name, the function must return a coding system or a cons cell containing two coding systems. This value is used as described above.
This variable is an alist specifying which coding systems to use for a subprocess, depending on which program is running in the subprocess. It works like
file-coding-system-alist, except that pattern is matched against the program name used to start the subprocess. The coding system or systems specified in this alist are used to initialize the coding systems used for I/O to the subprocess, but you can specify other coding systems later usingset-process-coding-system.
Warning: Coding systems such as undecided, which
determine the coding system from the data, do not work entirely reliably
with asynchronous subprocess output. This is because Emacs handles
asynchronous subprocess output in batches, as it arrives. If the coding
system leaves the character code conversion unspecified, or leaves the
end-of-line conversion unspecified, Emacs must try to detect the proper
conversion from one batch at a time, and this does not always work.
Therefore, with an asynchronous subprocess, if at all possible, use a
coding system which determines both the character code conversion and
the end of line conversion—that is, one like latin-1-unix,
rather than undecided or latin-1.
This variable is an alist that specifies the coding system to use for network streams. It works much like
file-coding-system-alist, with the difference that the pattern in an element may be either a port number or a regular expression. If it is a regular expression, it is matched against the network service name used to open the network stream.
This variable specifies the coding systems to use for subprocess (and network stream) input and output, when nothing else specifies what to do.
The value should be a cons cell of the form
(input-coding.output-coding). Here input-coding applies to input from the subprocess, and output-coding applies to output to it.
This function returns the coding system to use (by default) for performing operation with arguments. The value has this form:
(decoding-system encoding-system)The first element, decoding-system, is the coding system to use for decoding (in case operation does decoding), and encoding-system is the coding system for encoding (in case operation does encoding).
The argument operation should be a symbol, one of
insert-file-contents,write-region,call-process,call-process-region,start-process, oropen-network-stream. These are the names of the Emacs I/O primitives that can do coding system conversion.The remaining arguments should be the same arguments that might be given to that I/O primitive. Depending on the primitive, one of those arguments is selected as the target. For example, if operation does file I/O, whichever argument specifies the file name is the target. For subprocess primitives, the process name is the target. For
open-network-stream, the target is the service name or port number.This function looks up the target in
file-coding-system-alist,process-coding-system-alist, ornetwork-coding-system-alist, depending on operation. See Default Coding Systems.
You can specify the coding system for a specific operation by binding
the variables coding-system-for-read and/or
coding-system-for-write.
If this variable is non-
nil, it specifies the coding system to use for reading a file, or for input from a synchronous subprocess.It also applies to any asynchronous subprocess or network stream, but in a different way: the value of
coding-system-for-readwhen you start the subprocess or open the network stream specifies the input decoding method for that subprocess or network stream. It remains in use for that subprocess or network stream unless and until overridden.The right way to use this variable is to bind it with
letfor a specific I/O operation. Its global value is normallynil, and you should not globally set it to any other value. Here is an example of the right way to use the variable:;; Read the file with no character code conversion. ;; Assume crlf represents end-of-line. (let ((coding-system-for-write 'emacs-mule-dos)) (insert-file-contents filename))When its value is non-
nil,coding-system-for-readtakes precedence over all other methods of specifying a coding system to use for input, includingfile-coding-system-alist,process-coding-system-alistandnetwork-coding-system-alist.
This works much like
coding-system-for-read, except that it applies to output rather than input. It affects writing to files, as well as sending output to subprocesses and net connections.When a single operation does both input and output, as do
call-process-regionandstart-process, bothcoding-system-for-readandcoding-system-for-writeaffect it.
When this variable is non-
nil, no end-of-line conversion is done, no matter which coding system is specified. This applies to all the Emacs I/O and subprocess primitives, and to the explicit encoding and decoding functions (see Explicit Encoding).
All the operations that transfer text in and out of Emacs have the ability to use a coding system to encode or decode the text. You can also explicitly encode and decode text using the functions in this section.
The result of encoding, and the input to decoding, are not ordinary text. They logically consist of a series of byte values; that is, a series of characters whose codes are in the range 0 through 255. In a multibyte buffer or string, character codes 128 through 159 are represented by multibyte sequences, but this is invisible to Lisp programs.
The usual way to read a file into a buffer as a sequence of bytes, so
you can decode the contents explicitly, is with
insert-file-contents-literally (see Reading from Files);
alternatively, specify a non-nil rawfile argument when
visiting a file with find-file-noselect. These methods result in
a unibyte buffer.
The usual way to use the byte sequence that results from explicitly
encoding text is to copy it to a file or process—for example, to write
it with write-region (see Writing to Files), and suppress
encoding by binding coding-system-for-write to
no-conversion.
Here are the functions to perform explicit encoding or decoding. The decoding functions produce sequences of bytes; the encoding functions are meant to operate on sequences of bytes. All of these functions discard text properties.
This function encodes the text from start to end according to coding system coding-system. The encoded text replaces the original text in the buffer. The result of encoding is logically a sequence of bytes, but the buffer remains multibyte if it was multibyte before.
This function encodes the text in string according to coding system coding-system. It returns a new string containing the encoded text. The result of encoding is a unibyte string.
This function decodes the text from start to end according to coding system coding-system. The decoded text replaces the original text in the buffer. To make explicit decoding useful, the text before decoding ought to be a sequence of byte values, but both multibyte and unibyte buffers are acceptable.
This function decodes the text in string according to coding system coding-system. It returns a new string containing the decoded text. To make explicit decoding useful, the contents of string ought to be a sequence of byte values, but a multibyte string is acceptable.
Emacs can decode keyboard input using a coding system, and encode
terminal output. This is useful for terminals that transmit or display
text using a particular encoding such as Latin-1. Emacs does not set
last-coding-system-used for encoding or decoding for the
terminal.
This function returns the coding system that is in use for decoding keyboard input—or
nilif no coding system is to be used.
This function specifies coding-system as the coding system to use for decoding keyboard input. If coding-system is
nil, that means do not decode keyboard input.
This function returns the coding system that is in use for encoding terminal output—or
nilfor no encoding.
This function specifies coding-system as the coding system to use for encoding terminal output. If coding-system is
nil, that means do not encode terminal output.
On MS-DOS and Microsoft Windows, Emacs guesses the appropriate end-of-line conversion for a file by looking at the file's name. This feature classifies files as text files and binary files. By “binary file” we mean a file of literal byte values that are not necessarily meant to be characters; Emacs does no end-of-line conversion and no character code conversion for them. On the other hand, the bytes in a text file are intended to represent characters; when you create a new file whose name implies that it is a text file, Emacs uses DOS end-of-line conversion.
This variable, automatically buffer-local in each buffer, records the file type of the buffer's visited file. When a buffer does not specify a coding system with
buffer-file-coding-system, this variable is used to determine which coding system to use when writing the contents of the buffer. It should benilfor text,tfor binary. If it ist, the coding system isno-conversion. Otherwise,undecided-dosis used.Normally this variable is set by visiting a file; it is set to
nilif the file was visited without any actual conversion.
This variable holds an alist for recognizing text and binary files. Each element has the form (regexp . type), where regexp is matched against the file name, and type may be
nilfor text,tfor binary, or a function to call to compute which. If it is a function, then it is called with a single argument (the file name) and should returntornil.When running on MS-DOS or MS-Windows, Emacs checks this alist to decide which coding system to use when reading a file. For a text file,
undecided-dosis used. For a binary file,no-conversionis used.If no element in this alist matches a given file name, then
default-buffer-file-typesays how to treat the file.
This variable says how to handle files for which
file-name-buffer-file-type-alistsays nothing about the type.If this variable is non-
nil, then these files are treated as binary: the coding systemno-conversionis used. Otherwise, nothing special is done for them—the coding system is deduced solely from the file contents, in the usual Emacs fashion.
Input methods provide convenient ways of entering non-ascii characters from the keyboard. Unlike coding systems, which translate non-ascii characters to and from encodings meant to be read by programs, input methods provide human-friendly commands. (See Input Methods, for information on how users use input methods to enter text.) How to define input methods is not yet documented in this manual, but here we describe how to use them.
Each input method has a name, which is currently a string; in the future, symbols may also be usable as input method names.
This variable holds the name of the input method now active in the current buffer. (It automatically becomes local in each buffer when set in any fashion.) It is
nilif no input method is active in the buffer now.
This variable holds the default input method for commands that choose an input method. Unlike
current-input-method, this variable is normally global.
This function activates input method input-method for the current buffer. It also sets
default-input-methodto input-method. If input-method isnil, this function deactivates any input method for the current buffer.
This function reads an input method name with the minibuffer, prompting with prompt. If default is non-
nil, that is returned by default, if the user enters empty input. However, if inhibit-null is non-nil, empty input signals an error.The returned value is a string.
This variable defines all the supported input methods. Each element defines one input method, and should have the form:
(input-method language-env activate-func title description args...)Here input-method is the input method name, a string; language-env is another string, the name of the language environment this input method is recommended for. (That serves only for documentation purposes.)
activate-func is a function to call to activate this method. The args, if any, are passed as arguments to activate-func. All told, the arguments to activate-func are input-method and the args.
title is a string to display in the mode line while this method is active. description is a string describing this method and what it is good for.
The fundamental interface to input methods is through the
variable input-method-function. See Reading One Event.
POSIX defines a concept of “locales” which control which language to use in language-related features. These Emacs variables control how Emacs interacts with these features.
This variable specifies the coding system to use for decoding system error messages, for encoding the format argument to
format-time-string, and for decoding the return value offormat-time-string.
This variable specifies the locale to use for generating system error messages. Changing the locale can cause messages to come out in a different language or in a different orthography. If the variable is
nil, the locale is specified by environment variables in the usual POSIX fashion.
This variable specifies the locale to use for formatting time values. Changing the locale can cause messages to appear according to the conventions of a different language. If the variable is
nil, the locale is specified by environment variables in the usual POSIX fashion.
GNU Emacs provides two ways to search through a buffer for specified text: exact string searches and regular expression searches. After a regular expression search, you can examine the match data to determine which text matched the whole regular expression or various portions of it.
The ‘skip-chars...’ functions also perform a kind of searching. See Skipping Characters.
These are the primitive functions for searching through the text in a
buffer. They are meant for use in programs, but you may call them
interactively. If you do so, they prompt for the search string; the
arguments limit and noerror are nil, and repeat
is 1.
These search functions convert the search string to multibyte if the buffer is multibyte; they convert the search string to unibyte if the buffer is unibyte. See Text Representations.
This function searches forward from point for an exact match for string. If successful, it sets point to the end of the occurrence found, and returns the new value of point. If no match is found, the value and side effects depend on noerror (see below).
In the following example, point is initially at the beginning of the line. Then
(search-forward "fox")moves point after the last letter of ‘fox’:---------- Buffer: foo ---------- -!-The quick brown fox jumped over the lazy dog. ---------- Buffer: foo ---------- (search-forward "fox") => 20 ---------- Buffer: foo ---------- The quick brown fox-!- jumped over the lazy dog. ---------- Buffer: foo ----------The argument limit specifies the upper bound to the search. (It must be a position in the current buffer.) No match extending after that position is accepted. If limit is omitted or
nil, it defaults to the end of the accessible portion of the buffer.What happens when the search fails depends on the value of noerror. If noerror is
nil, asearch-failederror is signaled. If noerror ist,search-forwardreturnsniland does nothing. If noerror is neithernilnort, thensearch-forwardmoves point to the upper bound and returnsnil. (It would be more consistent now to return the new position of point in that case, but some existing programs may depend on a value ofnil.)If repeat is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time's match). If these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the search fails.
This function searches backward from point for string. It is just like
search-forwardexcept that it searches backwards and leaves point at the beginning of the match.
This function searches forward from point for a “word” match for string. If it finds a match, it sets point to the end of the match found, and returns the new value of point.
Word matching regards string as a sequence of words, disregarding punctuation that separates them. It searches the buffer for the same sequence of words. Each word must be distinct in the buffer (searching for the word ‘ball’ does not match the word ‘balls’), but the details of punctuation and spacing are ignored (searching for ‘ball boy’ does match ‘ball. Boy!’).
In this example, point is initially at the beginning of the buffer; the search leaves it between the ‘y’ and the ‘!’.
---------- Buffer: foo ---------- -!-He said "Please! Find the ball boy!" ---------- Buffer: foo ---------- (word-search-forward "Please find the ball, boy.") => 35 ---------- Buffer: foo ---------- He said "Please! Find the ball boy-!-!" ---------- Buffer: foo ----------If limit is non-
nil(it must be a position in the current buffer), then it is the upper bound to the search. The match found must not extend after that position.If noerror is
nil, thenword-search-forwardsignals an error if the search fails. If noerror ist, then it returnsnilinstead of signaling an error. If noerror is neithernilnort, it moves point to limit (or the end of the buffer) and returnsnil.If repeat is non-
nil, then the search is repeated that many times. Point is positioned at the end of the last match.
This function searches backward from point for a word match to string. This function is just like
word-search-forwardexcept that it searches backward and normally leaves point at the beginning of the match.
A regular expression (regexp, for short) is a pattern that denotes a (possibly infinite) set of strings. Searching for matches for a regexp is a very powerful operation. This section explains how to write regexps; the following section says how to search for them.
Regular expressions have a syntax in which a few characters are special constructs and the rest are ordinary. An ordinary character is a simple regular expression that matches that character and nothing else. The special characters are ‘.’, ‘*’, ‘+’, ‘?’, ‘[’, ‘]’, ‘^’, ‘$’, and ‘\’; no new special characters will be defined in the future. Any other character appearing in a regular expression is ordinary, unless a ‘\’ precedes it.
For example, ‘f’ is not a special character, so it is ordinary, and therefore ‘f’ is a regular expression that matches the string ‘f’ and no other string. (It does not match the string ‘fg’, but it does match a part of that string.) Likewise, ‘o’ is a regular expression that matches only ‘o’.
Any two regular expressions a and b can be concatenated. The result is a regular expression that matches a string if a matches some amount of the beginning of that string and b matches the rest of the string.
As a simple example, we can concatenate the regular expressions ‘f’ and ‘o’ to get the regular expression ‘fo’, which matches only the string ‘fo’. Still trivial. To do something more powerful, you need to use one of the special regular expression constructs.
Here is a list of the characters that are special in a regular expression.
‘*’ always applies to the smallest possible preceding expression. Thus, ‘fo*’ has a repeating ‘o’, not a repeating ‘fo’. It matches ‘f’, ‘fo’, ‘foo’, and so on.
The matcher processes a ‘*’ construct by matching, immediately, as many repetitions as can be found. Then it continues with the rest of the pattern. If that fails, backtracking occurs, discarding some of the matches of the ‘*’-modified construct in the hope that that will make it possible to match the rest of the pattern. For example, in matching ‘ca*ar’ against the string ‘caaar’, the ‘a*’ first tries to match all three ‘a’s; but the rest of the pattern is ‘ar’ and there is only ‘r’ left to match, so this try fails. The next alternative is for ‘a*’ to match only two ‘a’s. With this choice, the rest of the regexp matches successfully.
Nested repetition operators can be extremely slow if they specify
backtracking loops. For example, it could take hours for the regular
expression ‘\(x+y*\)*a’ to try to match the sequence
‘xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz’, before it ultimately fails.
The slowness is because Emacs must try each imaginable way of grouping
the 35 ‘x’s before concluding that none of them can work. To make
sure your regular expressions run fast, check nested repetitions
carefully.
For example, the regular expression ‘c[ad]*a’ when applied to the
string ‘cdaaada’ matches the whole string; but the regular
expression ‘c[ad]*?a’, applied to that same string, matches just
‘cda’. (The smallest possible match here for ‘[ad]*?’ that
permits the whole expression to match is ‘d’.)
Thus, ‘[ad]’ matches either one ‘a’ or one ‘d’, and ‘[ad]*’ matches any string composed of just ‘a’s and ‘d’s (including the empty string), from which it follows that ‘c[ad]*r’ matches ‘cr’, ‘car’, ‘cdr’, ‘caddaar’, etc.
You can also include character ranges in a character alternative, by writing the starting and ending characters with a ‘-’ between them. Thus, ‘[a-z]’ matches any lower-case ascii letter. Ranges may be intermixed freely with individual characters, as in ‘[a-z$%.]’, which matches any lower case ascii letter or ‘$’, ‘%’ or period.
Note that the usual regexp special characters are not special inside a character alternative. A completely different set of characters is special inside character alternatives: ‘]’, ‘-’ and ‘^’.
To include a ‘]’ in a character alternative, you must make it the first character. For example, ‘[]a]’ matches ‘]’ or ‘a’. To include a ‘-’, write ‘-’ as the first or last character of the character alternative, or put it after a range. Thus, ‘[]-]’ matches both ‘]’ and ‘-’.
To include ‘^’ in a character alternative, put it anywhere but at the beginning.
The beginning and end of a range of multibyte characters must be in
the same character set (see Character Sets). Thus,
"[\x8e0-\x97c]" is invalid because character 0x8e0 (‘a’
with grave accent) is in the Emacs character set for Latin-1 but the
character 0x97c (‘u’ with diaeresis) is in the Emacs character
set for Latin-2. (We use Lisp string syntax to write that example,
and a few others in the next few paragraphs, in order to include hex
escape sequences in them.)
If a range starts with a unibyte character c and ends with a multibyte character c2, the range is divided into two parts: one is ‘c..?\377’, the other is ‘c1..c2’, where c1 is the first character of the charset to which c2 belongs.
You cannot always match all non-ascii characters with the regular
expression "[\200-\377]". This works when searching a unibyte
buffer or string (see Text Representations), but not in a multibyte
buffer or string, because many non-ascii characters have codes
above octal 0377. However, the regular expression "[^\000-\177]"
does match all non-ascii characters (see below regarding ‘^’),
in both multibyte and unibyte representations, because only the
ascii characters are excluded.
Starting in Emacs 21, a character alternative can also specify named
character classes (see Char Classes). This is a POSIX feature whose
syntax is ‘[:class:]’. Using a character class is equivalent
to mentioning each of the characters in that class; but the latter is
not feasible in practice, since some classes include thousands of
different characters.
‘^’ is not special in a character alternative unless it is the first character. The character following the ‘^’ is treated as if it were first (in other words, ‘-’ and ‘]’ are not special there).
A complemented character alternative can match a newline, unless newline is
mentioned as one of the characters not to match. This is in contrast to
the handling of regexps in programs such as grep.
When matching a string instead of a buffer, ‘^’ matches at the beginning of the string or after a newline character.
For historical compatibility reasons, ‘^’ can be used only at the
beginning of the regular expression, or after ‘\(’ or ‘\|’.
When matching a string instead of a buffer, ‘$’ matches at the end of the string or before a newline character.
For historical compatibility reasons, ‘$’ can be used only at the
end of the regular expression, or before ‘\)’ or ‘\|’.
Because ‘\’ quotes special characters, ‘\$’ is a regular expression that matches only ‘$’, and ‘\[’ is a regular expression that matches only ‘[’, and so on.
Note that ‘\’ also has special meaning in the read syntax of Lisp
strings (see String Type), and must be quoted with ‘\’. For
example, the regular expression that matches the ‘\’ character is
‘\\’. To write a Lisp string that contains the characters
‘\\’, Lisp syntax requires you to quote each ‘\’ with another
‘\’. Therefore, the read syntax for a regular expression matching
‘\’ is "\\\\".
Please note: For historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, ‘*foo’ treats ‘*’ as ordinary since there is no preceding expression on which the ‘*’ can act. It is poor practice to depend on this behavior; quote the special character anyway, regardless of where it appears.
Here is a table of the classes you can use in a character alternative, in Emacs 21, and what they mean:
For the most part, ‘\’ followed by any character matches only that character. However, there are several exceptions: certain two-character sequences starting with ‘\’ that have special meanings. (The character after the ‘\’ in such a sequence is always ordinary when used on its own.) Here is a table of the special ‘\’ constructs.
Thus, ‘foo\|bar’ matches either ‘foo’ or ‘bar’ but no other string.
‘\|’ applies to the largest possible surrounding expressions. Only a surrounding ‘\( ... \)’ grouping can limit the grouping power of ‘\|’.
Full backtracking capability exists to handle multiple uses of
‘\|’, if you use the POSIX regular expression functions
(see POSIX Regexps).
For example, ‘c[ad]\{1,2\}r’ matches the strings ‘car’,
‘cdr’, ‘caar’, ‘cadr’, ‘cdar’, and ‘cddr’, and
nothing else.
‘\{0,1\}’ or ‘\{,1\}’ is equivalent to ‘?’.
‘\{0,\}’ or ‘\{,\}’ is equivalent to ‘*’.
‘\{1,\}’ is equivalent to ‘+’.
This last application is not a consequence of the idea of a
parenthetical grouping; it is a separate feature that was assigned as a
second meaning to the same ‘\( ... \)’ construct because, in
pratice, there was usually no conflict between the two meanings. But
occasionally there is a conflict, and that led to the introduction of
shy groups.
Shy groups are particulary useful for mechanically-constructed regular
expressions because they can be added automatically without altering the
numbering of any ordinary, non-shy groups.
In other words, after the end of a group, the matcher remembers the beginning and end of the text matched by that group. Later on in the regular expression you can use ‘\’ followed by digit to match that same text, whatever it may have been.
The strings matching the first nine grouping constructs appearing in the entire regular expression passed to a search or matching function are assigned numbers 1 through 9 in the order that the open parentheses appear in the regular expression. So you can use ‘\1’ through ‘\9’ to refer to the text matched by the corresponding grouping constructs.
For example, ‘\(.*\)\1’ matches any newline-free string that is composed of two identical halves. The ‘\(.*\)’ matches the first half, which may be anything, but the ‘\1’ that follows must match the same exact text.
If a particular grouping construct in the regular expression was never
matched—for instance, if it appears inside of an alternative that
wasn't used, or inside of a repetition that repeated zero times—then
the corresponding ‘\digit’ construct never matches
anything. To use an artificial example,, ‘\(foo\(b*\)\|lose\)\2’
cannot match ‘lose’: the second alternative inside the larger
group matches it, but then ‘\2’ is undefined and can't match
anything. But it can match ‘foobb’, because the first
alternative matches ‘foob’ and ‘\2’ matches ‘b’.
The following regular expression constructs match the empty string—that is, they don't use up any characters—but whether they match depends on the context.
‘\b’ matches at the beginning or end of the buffer
regardless of what text appears next to it.
Not every string is a valid regular expression. For example, a string
with unbalanced square brackets is invalid (with a few exceptions, such
as ‘[]]’), and so is a string that ends with a single ‘\’. If
an invalid regular expression is passed to any of the search functions,
an invalid-regexp error is signaled.
Here is a complicated regexp, used by Emacs to recognize the end of a
sentence together with any whitespace that follows. It is the value of
the variable sentence-end.
First, we show the regexp as a string in Lisp syntax to distinguish spaces from tab characters. The string constant begins and ends with a double-quote. ‘\"’ stands for a double-quote as part of the string, ‘\\’ for a backslash as part of the string, ‘\t’ for a tab and ‘\n’ for a newline.
"[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
In contrast, if you evaluate the variable sentence-end, you
will see the following:
sentence-end
=> "[.?!][]\"')}]*\\($\\| $\\| \\| \\)[
]*"
In this output, tab and newline appear as themselves.
This regular expression contains four parts in succession and can be deciphered as follows:
[.?!][]\"')}]*\" is Lisp syntax for a double-quote in
a string. The ‘*’ at the end indicates that the immediately
preceding regular expression (a character alternative, in this case) may be
repeated zero or more times.
\\($\\| $\\|\t\\| \\)[ \t\n]*These functions operate on regular expressions.
This function returns a regular expression whose only exact match is string. Using this regular expression in
looking-atwill succeed only if the next characters in the buffer are string; using it in a search function will succeed if the text being searched contains string.This allows you to request an exact string match or search when calling a function that wants a regular expression.
(regexp-quote "^The cat$") => "\\^The cat\\$"One use of
regexp-quoteis to combine an exact string match with context described as a regular expression. For example, this searches for the string that is the value of string, surrounded by whitespace:(re-search-forward (concat "\\s-" (regexp-quote string) "\\s-"))
This function returns an efficient regular expression that will match any of the strings strings. This is useful when you need to make matching or searching as fast as possible—for example, for Font Lock mode.
If the optional argument paren is non-
nil, then the returned regular expression is always enclosed by at least one parentheses-grouping construct.This simplified definition of
regexp-optproduces a regular expression which is equivalent to the actual value (but not as efficient):(defun regexp-opt (strings paren) (let ((open-paren (if paren "\\(" "")) (close-paren (if paren "\\)" ""))) (concat open-paren (mapconcat 'regexp-quote strings "\\|") close-paren)))
This function returns the total number of grouping constructs (parenthesized expressions) in regexp.
In GNU Emacs, you can search for the next match for a regular
expression either incrementally or not. For incremental search
commands, see Regular Expression Search. Here we describe only the search functions
useful in programs. The principal one is re-search-forward.
These search functions convert the regular expression to multibyte if the buffer is multibyte; they convert the regular expression to unibyte if the buffer is unibyte. See Text Representations.
This function searches forward in the current buffer for a string of text that is matched by the regular expression regexp. The function skips over any amount of text that is not matched by regexp, and leaves point at the end of the first match found. It returns the new value of point.
If limit is non-
nil(it must be a position in the current buffer), then it is the upper bound to the search. No match extending after that position is accepted.If repeat is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time's match). If all these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the function fails.
What happens when the function fails depends on the value of noerror. If noerror is
nil, asearch-failederror is signaled. If noerror ist,re-search-forwarddoes nothing and returnsnil. If noerror is neithernilnort, thenre-search-forwardmoves point to limit (or the end of the buffer) and returnsnil.In the following example, point is initially before the ‘T’. Evaluating the search call moves point to the end of that line (between the ‘t’ of ‘hat’ and the newline).
---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (re-search-forward "[a-z]+" nil t 5) => 27 ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ----------
This function searches backward in the current buffer for a string of text that is matched by the regular expression regexp, leaving point at the beginning of the first text found.
This function is analogous to
re-search-forward, but they are not simple mirror images.re-search-forwardfinds the match whose beginning is as close as possible to the starting point. Ifre-search-backwardwere a perfect mirror image, it would find the match whose end is as close as possible. However, in fact it finds the match whose beginning is as close as possible. The reason for this is that matching a regular expression at a given spot always works from beginning to end, and starts at a specified beginning position.A true mirror-image of
re-search-forwardwould require a special feature for matching regular expressions from end to beginning. It's not worth the trouble of implementing that.
This function returns the index of the start of the first match for the regular expression regexp in string, or
nilif there is no match. If start is non-nil, the search starts at that index in string.For example,
(string-match "quick" "The quick brown fox jumped quickly.") => 4 (string-match "quick" "The quick brown fox jumped quickly." 8) => 27The index of the first character of the string is 0, the index of the second character is 1, and so on.
After this function returns, the index of the first character beyond the match is available as
(match-end 0). See Match Data.(string-match "quick" "The quick brown fox jumped quickly." 8) => 27 (match-end 0) => 32
This function determines whether the text in the current buffer directly following point matches the regular expression regexp. “Directly following” means precisely that: the search is “anchored” and it can succeed only starting with the first character following point. The result is
tif so,nilotherwise.This function does not move point, but it updates the match data, which you can access using
match-beginningandmatch-end. See Match Data.In this example, point is located directly before the ‘T’. If it were anywhere else, the result would be
nil.---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-at "The cat in the hat$") => t
The usual regular expression functions do backtracking when necessary to handle the ‘\|’ and repetition constructs, but they continue this only until they find some match. Then they succeed and report the first match found.
This section describes alternative search functions which perform the full backtracking specified by the POSIX standard for regular expression matching. They continue backtracking until they have tried all possibilities and found all matches, so they can report the longest match, as required by POSIX. This is much slower, so use these functions only when you really need the longest match.
This is like
re-search-forwardexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
This is like
re-search-backwardexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
This is like
looking-atexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
This is like
string-matchexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
This function is the guts of
query-replaceand related commands. It searches for occurrences of from-string in the text between positions start and end and replaces some or all of them. If start isnil, point is used instead, and the buffer's end is used for end.If query-flag is
nil, it replaces all occurrences; otherwise, it asks the user what to do about each one.If regexp-flag is non-
nil, then from-string is considered a regular expression; otherwise, it must match literally. If delimited-flag is non-nil, then only replacements surrounded by word boundaries are considered.The argument replacements specifies what to replace occurrences with. If it is a string, that string is used. It can also be a list of strings, to be used in cyclic order.
If replacements is a cons cell,
(function.data), this means to call function after each match to get the replacement text. This function is called with two arguments: data, and the number of replacements already made.If repeat-count is non-
nil, it should be an integer. Then it specifies how many times to use each of the strings in the replacements list before advancing cyclicly to the next one.If from-string contains upper-case letters, then
perform-replacebindscase-fold-searchtonil, and it uses thereplacementswithout altering the case of them.Normally, the keymap
query-replace-mapdefines the possible user responses for queries. The argument map, if non-nil, is a keymap to use instead ofquery-replace-map.
This variable holds a special keymap that defines the valid user responses for
query-replaceand related functions, as well asy-or-n-pandmap-y-or-n-p. It is unusual in two ways:
- The “key bindings” are not commands, just symbols that are meaningful to the functions that use this map.
- Prefix keys are not supported; each key binding must be for a single-event key sequence. This is because the functions don't use
read-key-sequenceto get the input; instead, they read a single event and look it up “by hand.”
Here are the meaningful “bindings” for query-replace-map.
Several of them are meaningful only for query-replace and
friends.
actskipexitact-and-exitact-and-showautomaticbackupeditdelete-and-editrecenterquity-or-n-p and related functions
use this answer.
helpEmacs keeps track of the start and end positions of the segments of text found during a regular expression search. This means, for example, that you can search for a complex pattern, such as a date in an Rmail message, and then extract parts of the match under control of the pattern.
Because the match data normally describe the most recent search only, you must be careful not to do another search inadvertently between the search you wish to refer back to and the use of the match data. If you can't avoid another intervening search, you must save and restore the match data around it, to prevent it from being overwritten.
This function replaces the text matched by the last search with replacement.
This function replaces the text in the buffer (or in string) that was matched by the last search. It replaces that text with replacement.
If you did the last search in a buffer, you should specify
nilfor string. Thenreplace-matchdoes the replacement by editing the buffer; it leaves point at the end of the replacement text, and returnst.If you did the search in a string, pass the same string as string. Then
replace-matchdoes the replacement by constructing and returning a new string.If fixedcase is non-
nil, then the case of the replacement text is not changed; otherwise, the replacement text is converted to a different case depending upon the capitalization of the text to be replaced. If the original text is all upper case, the replacement text is converted to upper case. If the first word of the original text is capitalized, then the first word of the replacement text is capitalized. If the original text contains just one word, and that word is a capital letter,replace-matchconsiders this a capitalized first word rather than all upper case.If literal is non-
nil, then replacement is inserted exactly as it is, the only alterations being case changes as needed. If it isnil(the default), then the character ‘\’ is treated specially. If a ‘\’ appears in replacement, then it must be part of one of the following sequences:
- ‘\&’
- ‘\&’ stands for the entire text being replaced.
- ‘\n’
- ‘\n’, where n is a digit, stands for the text that matched the nth subexpression in the original regexp. Subexpressions are those expressions grouped inside ‘\(...\)’.
- ‘\\’
- ‘\\’ stands for a single ‘\’ in the replacement text.
If subexp is non-
nil, that says to replace just subexpression number subexp of the regexp that was matched, not the entire match. For example, after matching ‘foo \(ba*r\)’, callingreplace-matchwith 1 as subexp means to replace just the text that matched ‘\(ba*r\)’.
This section explains how to use the match data to find out what was matched by the last search or match operation.
You can ask about the entire matching text, or about a particular parenthetical subexpression of a regular expression. The count argument in the functions below specifies which. If count is zero, you are asking about the entire match. If count is positive, it specifies which subexpression you want.
Recall that the subexpressions of a regular expression are those expressions grouped with escaped parentheses, ‘\(...\)’. The countth subexpression is found by counting occurrences of ‘\(’ from the beginning of the whole regular expression. The first subexpression is numbered 1, the second 2, and so on. Only regular expressions can have subexpressions—after a simple string search, the only information available is about the entire match.
A search which fails may or may not alter the match data. In the past, a failing search did not do this, but we may change it in the future.
This function returns, as a string, the text matched in the last search or match operation. It returns the entire text if count is zero, or just the portion corresponding to the countth parenthetical subexpression, if count is positive.
If the last such operation was done against a string with
string-match, then you should pass the same string as the argument in-string. After a buffer search or match, you should omit in-string or passnilfor it; but you should make sure that the current buffer when you callmatch-stringis the one in which you did the searching or matching.The value is
nilif count is out of range, or for a subexpression inside a ‘\|’ alternative that wasn't used or a repetition that repeated zero times.
This function is like
match-stringexcept that the result has no text properties.
This function returns the position of the start of text matched by the last regular expression searched for, or a subexpression of it.
If count is zero, then the value is the position of the start of the entire match. Otherwise, count specifies a subexpression in the regular expression, and the value of the function is the starting position of the match for that subexpression.
The value is
nilfor a subexpression inside a ‘\|’ alternative that wasn't used or a repetition that repeated zero times.
This function is like
match-beginningexcept that it returns the position of the end of the match, rather than the position of the beginning.
Here is an example of using the match data, with a comment showing the positions within the text:
(string-match "\\(qu\\)\\(ick\\)"
"The quick fox jumped quickly.")
;0123456789
=> 4
(match-string 0 "The quick fox jumped quickly.")
=> "quick"
(match-string 1 "The quick fox jumped quickly.")
=> "qu"
(match-string 2 "The quick fox jumped quickly.")
=> "ick"
(match-beginning 1) ; The beginning of the match
=> 4 ; with ‘qu’ is at index 4.
(match-beginning 2) ; The beginning of the match
=> 6 ; with ‘ick’ is at index 6.
(match-end 1) ; The end of the match
=> 6 ; with ‘qu’ is at index 6.
(match-end 2) ; The end of the match
=> 9 ; with ‘ick’ is at index 9.
Here is another example. Point is initially located at the beginning of the line. Searching moves point to between the space and the word ‘in’. The beginning of the entire match is at the 9th character of the buffer (‘T’), and the beginning of the match for the first subexpression is at the 13th character (‘c’).
(list
(re-search-forward "The \\(cat \\)")
(match-beginning 0)
(match-beginning 1))
=> (9 9 13)
---------- Buffer: foo ----------
I read "The cat -!-in the hat comes back" twice.
^ ^
9 13
---------- Buffer: foo ----------
(In this case, the index returned is a buffer position; the first character of the buffer counts as 1.)
The functions match-data and set-match-data read or
write the entire match data, all at once.
This function returns a newly constructed list containing all the information on what text the last search matched. Element zero is the position of the beginning of the match for the whole expression; element one is the position of the end of the match for the expression. The next two elements are the positions of the beginning and end of the match for the first subexpression, and so on. In general, element number 2n corresponds to
(match-beginningn); and element number 2n + 1 corresponds to(match-endn).All the elements are markers or
nilif matching was done on a buffer, and all are integers ornilif matching was done on a string withstring-match.As always, there must be no possibility of intervening searches between the call to a search function and the call to
match-datathat is intended to access the match data for that search.(match-data) => (#<marker at 9 in foo> #<marker at 17 in foo> #<marker at 13 in foo> #<marker at 17 in foo>)
This function sets the match data from the elements of match-list, which should be a list that was the value of a previous call to
match-data.If match-list refers to a buffer that doesn't exist, you don't get an error; that sets the match data in a meaningless but harmless way.
store-match-datais a semi-obsolete alias forset-match-data.
When you call a function that may do a search, you may need to save and restore the match data around that call, if you want to preserve the match data from an earlier search for later use. Here is an example that shows the problem that arises if you fail to save the match data:
(re-search-forward "The \\(cat \\)")
=> 48
(foo) ; Perhaps foo does
; more searching.
(match-end 0)
=> 61 ; Unexpected result---not 48!
You can save and restore the match data with save-match-data:
This macro executes body, saving and restoring the match data around it.
You could use set-match-data together with match-data to
imitate the effect of the special form save-match-data. Here is
how:
(let ((data (match-data)))
(unwind-protect
... ; Ok to change the original match data.
(set-match-data data)))
Emacs automatically saves and restores the match data when it runs process filter functions (see Filter Functions) and process sentinels (see Sentinels).
By default, searches in Emacs ignore the case of the text they are searching through; if you specify searching for ‘FOO’, then ‘Foo’ or ‘foo’ is also considered a match. This applies to regular expressions, too; thus, ‘[aB]’ would match ‘a’ or ‘A’ or ‘b’ or ‘B’.
If you do not want this feature, set the variable
case-fold-search to nil. Then all letters must match
exactly, including case. This is a buffer-local variable; altering the
variable affects only the current buffer. (See Intro to Buffer-Local.) Alternatively, you may change the value of
default-case-fold-search, which is the default value of
case-fold-search for buffers that do not override it.
Note that the user-level incremental search feature handles case distinctions differently. When given a lower case letter, it looks for a match of either case, but when given an upper case letter, it looks for an upper case letter only. But this has nothing to do with the searching functions used in Lisp code.
This variable determines whether the replacement functions should preserve case. If the variable is
nil, that means to use the replacement text verbatim. A non-nilvalue means to convert the case of the replacement text according to the text being replaced.This variable is used by passing it as an argument to the function
replace-match. See Replacing Match.
This buffer-local variable determines whether searches should ignore case. If the variable is
nilthey do not ignore case; otherwise they do ignore case.
The value of this variable is the default value for
case-fold-searchin buffers that do not override it. This is the same as(default-value 'case-fold-search).
This section describes some variables that hold regular expressions used for certain purposes in editing:
This is the regular expression describing line-beginnings that separate pages. The default value is
"^\014"(i.e.,"^^L"or"^\C-l"); this matches a line that starts with a formfeed character.
The following two regular expressions should not assume the match always starts at the beginning of a line; they should not use ‘^’ to anchor the match. Most often, the paragraph commands do check for a match only at the beginning of a line, which means that ‘^’ would be superfluous. When there is a nonzero left margin, they accept matches that start after the left margin. In that case, a ‘^’ would be incorrect. However, a ‘^’ is harmless in modes where a left margin is never used.
This is the regular expression for recognizing the beginning of a line that separates paragraphs. (If you change this, you may have to change
paragraph-startalso.) The default value is"[ \t\f]*$", which matches a line that consists entirely of spaces, tabs, and form feeds (after its left margin).
This is the regular expression for recognizing the beginning of a line that starts or separates paragraphs. The default value is
"[ \t\n\f]", which matches a line starting with a space, tab, newline, or form feed (after its left margin).
This is the regular expression describing the end of a sentence. (All paragraph boundaries also end sentences, regardless.) The default value is:
"[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"This means a period, question mark or exclamation mark, followed optionally by a closing parenthetical character, followed by tabs, spaces or new lines.
For a detailed explanation of this regular expression, see Regexp Example.
A syntax table specifies the syntactic textual function of each character. This information is used by the parsing functions, the complex movement commands, and others to determine where words, symbols, and other syntactic constructs begin and end. The current syntax table controls the meaning of the word motion functions (see Word Motion) and the list motion functions (see List Motion), as well as the functions in this chapter.
A syntax table provides Emacs with the information that determines the syntactic use of each character in a buffer. This information is used by the parsing commands, the complex movement commands, and others to determine where words, symbols, and other syntactic constructs begin and end. The current syntax table controls the meaning of the word motion functions (see Word Motion) and the list motion functions (see List Motion) as well as the functions in this chapter.
A syntax table is a char-table (see Char-Tables). The element at index c describes the character with code c. The element's value should be a list that encodes the syntax of the character in question.
Syntax tables are used only for moving across text, not for the Emacs Lisp reader. Emacs Lisp uses built-in syntactic rules when reading Lisp expressions, and these rules cannot be changed. (Some Lisp systems provide ways to redefine the read syntax, but we decided to leave this feature out of Emacs Lisp for simplicity.)
Each buffer has its own major mode, and each major mode has its own idea of the syntactic class of various characters. For example, in Lisp mode, the character ‘;’ begins a comment, but in C mode, it terminates a statement. To support these variations, Emacs makes the choice of syntax table local to each buffer. Typically, each major mode has its own syntax table and installs that table in each buffer that uses that mode. Changing this table alters the syntax in all those buffers as well as in any buffers subsequently put in that mode. Occasionally several similar modes share one syntax table. See Example Major Modes, for an example of how to set up a syntax table.
A syntax table can inherit the data for some characters from the standard syntax table, while specifying other characters itself. The “inherit” syntax class means “inherit this character's syntax from the standard syntax table.” Just changing the standard syntax for a character affects all syntax tables that inherit from it.
This section describes the syntax classes and flags that denote the
syntax of a character, and how they are represented as a syntax
descriptor, which is a Lisp string that you pass to
modify-syntax-entry to specify the syntax you want.
The syntax table specifies a syntax class for each character. There is no necessary relationship between the class of a character in one syntax table and its class in any other table.
Each class is designated by a mnemonic character, which serves as the name of the class when you need to specify a class. Usually the designator character is one that is often assigned that class; however, its meaning as a designator is unvarying and independent of what syntax that character currently has. Thus, ‘\’ as a designator character always gives “escape character” syntax, regardless of what syntax ‘\’ currently has.
A syntax descriptor is a Lisp string that specifies a syntax class, a matching character (used only for the parenthesis classes) and flags. The first character is the designator for a syntax class. The second character is the character to match; if it is unused, put a space there. Then come the characters for any desired flags. If no matching character or flags are needed, one character is sufficient.
For example, the syntax descriptor for the character ‘*’ in C mode is ‘. 23’ (i.e., punctuation, matching character slot unused, second character of a comment-starter, first character of a comment-ender), and the entry for ‘/’ is ‘. 14’ (i.e., punctuation, matching character slot unused, first character of a comment-starter, second character of a comment-ender).
Here is a table of syntax classes, the characters that stand for them, their meanings, and examples of their use.
Whitespace characters (designated by ‘ ’ or ‘-’) separate symbols and words from each other. Typically, whitespace characters have no other syntactic significance, and multiple whitespace characters are syntactically equivalent to a single one. Space, tab, newline and formfeed are classified as whitespace in almost all major modes.
Word constituents (designated by ‘w’) are parts of normal English words and are typically used in variable and command names in programs. All upper- and lower-case letters, and the digits, are typically word constituents.
Symbol constituents (designated by ‘_’) are the extra characters that are used in variable and command names along with word constituents. For example, the symbol constituents class is used in Lisp mode to indicate that certain characters may be part of symbol names even though they are not part of English words. These characters are ‘$&*+-_<>’. In standard C, the only non-word-constituent character that is valid in symbols is underscore (‘_’).
Punctuation characters (designated by ‘.’) are those characters that are used as punctuation in English, or are used in some way in a programming language to separate symbols from one another. Most programming language modes, including Emacs Lisp mode, have no characters in this class since the few characters that are not symbol or word constituents all have other uses.
Open and close parenthesis characters are characters used in dissimilar pairs to surround sentences or expressions. Such a grouping is begun with an open parenthesis character and terminated with a close. Each open parenthesis character matches a particular close parenthesis character, and vice versa. Normally, Emacs indicates momentarily the matching open parenthesis when you insert a close parenthesis. See Blinking.
The class of open parentheses is designated by ‘(’, and that of close parentheses by ‘)’.
In English text, and in C code, the parenthesis pairs are ‘()’, ‘[]’, and ‘{}’. In Emacs Lisp, the delimiters for lists and vectors (‘()’ and ‘[]’) are classified as parenthesis characters.
String quote characters (designated by ‘"’) are used in many languages, including Lisp and C, to delimit string constants. The same string quote character appears at the beginning and the end of a string. Such quoted strings do not nest.
The parsing facilities of Emacs consider a string as a single token. The usual syntactic meanings of the characters in the string are suppressed.
The Lisp modes have two string quote characters: double-quote (‘"’) and vertical bar (‘|’). ‘|’ is not used in Emacs Lisp, but it is used in Common Lisp. C also has two string quote characters: double-quote for strings, and single-quote (‘'’) for character constants.
English text has no string quote characters because English is not a programming language. Although quotation marks are used in English, we do not want them to turn off the usual syntactic properties of other characters in the quotation.
An escape character (designated by ‘\’) starts an escape sequence such as is used in C string and character constants. The character ‘\’ belongs to this class in both C and Lisp. (In C, it is used thus only inside strings, but it turns out to cause no trouble to treat it this way throughout C code.)
Characters in this class count as part of words if
words-include-escapesis non-nil. See Word Motion.
A character quote character (designated by ‘/’) quotes the following character so that it loses its normal syntactic meaning. This differs from an escape character in that only the character immediately following is ever affected.
Characters in this class count as part of words if
words-include-escapesis non-nil. See Word Motion.This class is used for backslash in TeX mode.
Paired delimiter characters (designated by ‘$’) are like string quote characters except that the syntactic properties of the characters between the delimiters are not suppressed. Only TeX mode uses a paired delimiter presently—the ‘$’ that both enters and leaves math mode.
An expression prefix operator (designated by ‘'’) is used for syntactic operators that are considered as part of an expression if they appear next to one. In Lisp modes, these characters include the apostrophe, ‘'’ (used for quoting), the comma, ‘,’ (used in macros), and ‘#’ (used in the read syntax for certain data types).
The comment starter and comment ender characters are used in various languages to delimit comments. These classes are designated by ‘<’ and ‘>’, respectively.
English text has no comment characters. In Lisp, the semicolon (‘;’) starts a comment and a newline or formfeed ends one.
This syntax class does not specify a particular syntax. It says to look in the standard syntax table to find the syntax of this character. The designator for this syntax code is ‘@’.
A generic comment delimiter (designated by ‘!’) starts or ends a special kind of comment. Any generic comment delimiter matches any generic comment delimiter, but they cannot match a comment starter or comment ender; generic comment delimiters can only match each other.
This syntax class is primarily meant for use with the
syntax-tabletext property (see Syntax Properties). You can mark any range of characters as forming a comment, by giving the first and last characters of the rangesyntax-tableproperties identifying them as generic comment delimiters.
A generic string delimiter (designated by ‘|’) starts or ends a string. This class differs from the string quote class in that any generic string delimiter can match any other generic string delimiter; but they do not match ordinary string quote characters.
This syntax class is primarily meant for use with the
syntax-tabletext property (see Syntax Properties). You can mark any range of characters as forming a string constant, by giving the first and last characters of the rangesyntax-tableproperties identifying them as generic string delimiters.
In addition to the classes, entries for characters in a syntax table can specify flags. There are seven possible flags, represented by the characters ‘1’, ‘2’, ‘3’, ‘4’, ‘b’, ‘n’, and ‘p’.
All the flags except ‘n’ and ‘p’ are used to describe multi-character comment delimiters. The digit flags indicate that a character can also be part of a comment sequence, in addition to the syntactic properties associated with its character class. The flags are independent of the class and each other for the sake of characters such as ‘*’ in C mode, which is a punctuation character, and the second character of a start-of-comment sequence (‘/*’), and the first character of an end-of-comment sequence (‘*/’).
Here is a table of the possible flags for a character c, and what they mean:
Emacs supports two comment styles simultaneously in any one syntax table. This is for the sake of C++. Each style of comment syntax has its own comment-start sequence and its own comment-end sequence. Each comment must stick to one style or the other; thus, if it starts with the comment-start sequence of style “b”, it must also end with the comment-end sequence of style “b”.
The two comment-start sequences must begin with the same character; only the second character may differ. Mark the second character of the “b”-style comment-start sequence with the ‘b’ flag.
A comment-end sequence (one or two characters) applies to the “b” style if its first character has the ‘b’ flag set; otherwise, it applies to the “a” style.
The appropriate comment syntax settings for C++ are as follows:
This defines four comment-delimiting sequences:
The function backward-prefix-chars moves back over these
characters, as well as over characters whose primary syntax class is
prefix (‘'’). See Motion and Syntax.
In this section we describe functions for creating, accessing and altering syntax tables.
This function creates a new syntax table. It inherits the syntax for letters and control characters from the standard syntax table. For other characters, the syntax is copied from the standard syntax table.
Most major mode syntax tables are created in this way.
This function constructs a copy of table and returns it. If table is not supplied (or is
nil), it returns a copy of the current syntax table. Otherwise, an error is signaled if table is not a syntax table.
This function sets the syntax entry for char according to syntax-descriptor. The syntax is changed only for table, which defaults to the current buffer's syntax table, and not in any other syntax table. The argument syntax-descriptor specifies the desired syntax; this is a string beginning with a class designator character, and optionally containing a matching character and flags as well. See Syntax Descriptors.
This function always returns
nil. The old syntax information in the table for this character is discarded.An error is signaled if the first character of the syntax descriptor is not one of the twelve syntax class designator characters. An error is also signaled if char is not a character.
Examples:
;; Put the space character in class whitespace. (modify-syntax-entry ?\ " ") => nil ;; Make ‘$’ an open parenthesis character, ;; with ‘^’ as its matching close. (modify-syntax-entry ?$ "(^") => nil ;; Make ‘^’ a close parenthesis character, ;; with ‘$’ as its matching open. (modify-syntax-entry ?^ ")$") => nil ;; Make ‘/’ a punctuation character, ;; the first character of a start-comment sequence, ;; and the second character of an end-comment sequence. ;; This is used in C mode. (modify-syntax-entry ?/ ". 14") => nil
This function returns the syntax class of character, represented by its mnemonic designator character. This returns only the class, not any matching parenthesis or flags.
An error is signaled if char is not a character.
The following examples apply to C mode. The first example shows that the syntax class of space is whitespace (represented by a space). The second example shows that the syntax of ‘/’ is punctuation. This does not show the fact that it is also part of comment-start and -end sequences. The third example shows that open parenthesis is in the class of open parentheses. This does not show the fact that it has a matching character, ‘)’.
(string (char-syntax ?\ )) => " " (string (char-syntax ?/)) => "." (string (char-syntax ?\()) => "("We use
stringto make it easier to see the character returned bychar-syntax.
This function makes table the syntax table for the current buffer. It returns table.
This function returns the current syntax table, which is the table for the current buffer.
This macro executes body using table as the current syntax table. It returns the value of the last form in body, after restoring the old current syntax table.
Since each buffer has its own current syntax table, we should make that more precise:
with-syntax-tabletemporarily alters the current syntax table of whichever buffer is current at the time the macro execution starts. Other buffers are not affected.
When the syntax table is not flexible enough to specify the syntax of a
language, you can use syntax-table text properties to override
the syntax table for specific character occurrences in the buffer.
See Text Properties.
The valid values of syntax-table text property are:
(syntax-code . matching-char)nilnil, the character's syntax is determined from
the current syntax table in the usual way.
If this is non-
nil, the syntax scanning functions pay attention to syntax text properties. Otherwise they use only the current syntax table.
This section describes functions for moving across characters that have certain syntax classes.
This function moves point forward across characters having syntax classes mentioned in syntaxes. It stops when it encounters the end of the buffer, or position limit (if specified), or a character it is not supposed to skip.
If syntaxes starts with ‘^’, then the function skips characters whose syntax is not in syntaxes.
The return value is the distance traveled, which is a nonnegative integer.
This function moves point backward across characters whose syntax classes are mentioned in syntaxes. It stops when it encounters the beginning of the buffer, or position limit (if specified), or a character it is not supposed to skip.
If syntaxes starts with ‘^’, then the function skips characters whose syntax is not in syntaxes.
The return value indicates the distance traveled. It is an integer that is zero or less.
This function moves point backward over any number of characters with expression prefix syntax. This includes both characters in the expression prefix syntax class, and characters with the ‘p’ flag.
Here are several functions for parsing and scanning balanced expressions, also known as sexps, in which parentheses match in pairs. The syntax table controls the interpretation of characters, so these functions can be used for Lisp expressions when in Lisp mode and for C expressions when in C mode. See List Motion, for convenient higher-level functions for moving over balanced expressions.
This function parses a sexp in the current buffer starting at start, not scanning past limit. It stops at position limit or when certain criteria described below are met, and sets point to the location where parsing stops. It returns a value describing the status of the parse at the point where it stops.
If state is
nil, start is assumed to be at the top level of parenthesis structure, such as the beginning of a function definition. Alternatively, you might wish to resume parsing in the middle of the structure. To do this, you must provide a state argument that describes the initial status of parsing.If the third argument target-depth is non-
nil, parsing stops if the depth in parentheses becomes equal to target-depth. The depth starts at 0, or at whatever is given in state.If the fourth argument stop-before is non-
nil, parsing stops when it comes to any character that starts a sexp. If stop-comment is non-nil, parsing stops when it comes to the start of a comment. If stop-comment is the symbolsyntax-table, parsing stops after the start of a comment or a string, or the end of a comment or a string, whichever comes first.The fifth argument state is a nine-element list of the same form as the value of this function, described below. (It is OK to omit the last element of the nine.) The return value of one call may be used to initialize the state of the parse on another call to
parse-partial-sexp.The result is a list of nine elements describing the final state of the parse:
- The depth in parentheses, counting from 0.
- The character position of the start of the innermost parenthetical grouping containing the stopping point;
nilif none.- The character position of the start of the last complete subexpression terminated;
nilif none.- Non-
nilif inside a string. More precisely, this is the character that will terminate the string, ortif a generic string delimiter character should terminate it.tif inside a comment (of either style), or the comment nesting level if inside a kind of comment that can be nested.tif point is just after a quote character.- The minimum parenthesis depth encountered during this scan.
- What kind of comment is active:
nilfor a comment of style “a”,tfor a comment of style “b”, andsyntax-tablefor a comment that should be ended by a generic comment delimiter character.- The string or comment start position. While inside a comment, this is the position where the comment began; while inside a string, this is the position where the string began. When outside of strings and comments, this element is
nil.Elements 0, 3, 4, 5 and 7 are significant in the argument state.
This function is most often used to compute indentation for languages that have nested parentheses.
This function scans forward count balanced parenthetical groupings from position from. It returns the position where the scan stops. If count is negative, the scan moves backwards.
If depth is nonzero, parenthesis depth counting begins from that value. The only candidates for stopping are places where the depth in parentheses becomes zero;
scan-listscounts count such places and then stops. Thus, a positive value for depth means go out depth levels of parenthesis.Scanning ignores comments if
parse-sexp-ignore-commentsis non-nil.If the scan reaches the beginning or end of the buffer (or its accessible portion), and the depth is not zero, an error is signaled. If the depth is zero but the count is not used up,
nilis returned.
This function scans forward count sexps from position from. It returns the position where the scan stops. If count is negative, the scan moves backwards.
Scanning ignores comments if
parse-sexp-ignore-commentsis non-nil.If the scan reaches the beginning or end of (the accessible part of) the buffer while in the middle of a parenthetical grouping, an error is signaled. If it reaches the beginning or end between groupings but before count is used up,
nilis returned.
If this variable is non-
nil,scan-sexpstreats all non-ascii characters as symbol constituents regardless of what the syntax table says about them. (However, text properties can still override the syntax.)
If the value is non-
nil, then comments are treated as whitespace by the functions in this section and byforward-sexp.In older Emacs versions, this feature worked only when the comment terminator is something like ‘*/’, and appears only to end a comment. In languages where newlines terminate comments, it was necessary make this variable
nil, since not every newline is the end of a comment. This limitation no longer exists.
You can use forward-comment to move forward or backward over
one comment or several comments.
This function moves point forward across count comments (backward, if count is negative). If it finds anything other than a comment or whitespace, it stops, leaving point at the place where it stopped. It also stops after satisfying count.
To move forward over all comments and whitespace following point, use
(forward-comment (buffer-size)). (buffer-size) is a good
argument to use, because the number of comments in the buffer cannot
exceed that many.
Most of the major modes in Emacs have their own syntax tables. Here are several of them:
This function returns the standard syntax table, which is the syntax table used in Fundamental mode.
The value of this variable is the syntax table used in Text mode.
The value of this variable is the syntax table used in Emacs Lisp mode by editing commands. (It has no effect on the Lisp
readfunction.)
Lisp programs don't usually work with the elements directly; the Lisp-level syntax table functions usually work with syntax descriptors (see Syntax Descriptors). Nonetheless, here we document the internal format. This format is used mostly when manipulating syntax properties.
Each element of a syntax table is a cons cell of the form
(syntax-code . matching-char). The car,
syntax-code, is an integer that encodes the syntax class, and any
flags. The cdr, matching-char, is non-nil if
a character to match was specified.
This table gives the value of syntax-code which corresponds to each syntactic type.
| Integer Class | Integer Class |
Integer Class
| |
| 0 whitespace | 5 close parenthesis |
10 character quote
| |
| 1 punctuation | 6 expression prefix |
11 comment-start
| |
| 2 word | 7 string quote |
12 comment-end
| |
| 3 symbol | 8 paired delimiter |
13 inherit
| |
| 4 open parenthesis | 9 escape |
14 comment-fence
| |
|
15 string-fence
|
For example, the usual syntax value for ‘(’ is (4 . 41).
(41 is the character code for ‘)’.)
The flags are encoded in higher order bits, starting 16 bits from the least significant bit. This table gives the power of two which corresponds to each syntax flag.
| Prefix Flag | Prefix Flag |
Prefix Flag
| |
‘1’ (lsh 1 16)
|
‘4’ (lsh 1 19)
|
‘b’ (lsh 1 21)
| |
‘2’ (lsh 1 17)
|
‘p’ (lsh 1 20)
|
‘n’ (lsh 1 22)
| |
‘3’ (lsh 1 18)
|
This function returns the internal form
(syntax-code.matching-char)corresponding to the syntax descriptor desc.
Categories provide an alternate way of classifying characters syntactically. You can define several categories as needed, then independently assign each character to one or more categories. Unlike syntax classes, categories are not mutually exclusive; it is normal for one character to belong to several categories.
Each buffer has a category table which records which categories are defined and also which characters belong to each category. Each category table defines its own categories, but normally these are initialized by copying from the standard categories table, so that the standard categories are available in all modes.
Each category has a name, which is an ascii printing character in
the range ‘ ’ to ‘~’. You specify the name of a category
when you define it with define-category.
The category table is actually a char-table (see Char-Tables).
The element of the category table at index c is a category
set—a bool-vector—that indicates which categories character c
belongs to. In this category set, if the element at index cat is
t, that means category cat is a member of the set, and that
character c belongs to category cat.
This function defines a new category, with name char and documentation docstring.
The new category is defined for category table table, which defaults to the current buffer's category table.
This function returns the documentation string of category category in category table table.
(category-docstring ?a) => "ASCII" (category-docstring ?l) => "Latin"
This function returns a category name (a character) which is not currently defined in table. If all possible categories are in use in table, it returns
nil.
This function returns
tif object is a category table, otherwisenil.
This function constructs a copy of table and returns it. If table is not supplied (or is
nil), it returns a copy of the current category table. Otherwise, an error is signaled if table is not a category table.
This function makes table the category table for the current buffer. It returns table.
This creates and returns an empty category table. In an empty category table, no categories have been allocated, and no characters belong to any categories.
This function returns a new category set—a bool-vector—whose initial contents are the categories listed in the string categories. The elements of categories should be category names; the new category set has
tfor each of those categories, andnilfor all other categories.(make-category-set "al") => #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
This function returns the category set for character char. This is the bool-vector which records which categories the character char belongs to. The function
char-category-setdoes not allocate storage, because it returns the same bool-vector that exists in the category table.(char-category-set ?a) => #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
This function converts the category set category-set into a string containing the characters that designate the categories that are members of the set.
(category-set-mnemonics (char-category-set ?a)) => "al"
This function modifies the category set of character in category table table (which defaults to the current buffer's category table).
Normally, it modifies the category set by adding category to it. But if reset is non-
nil, then it deletes category instead.
This function describes the category specifications in the current category table. The descriptions are inserted in a buffer, which is then displayed.
An abbreviation or abbrev is a string of characters that may be expanded to a longer string. The user can insert the abbrev string and find it replaced automatically with the expansion of the abbrev. This saves typing.
The set of abbrevs currently in effect is recorded in an abbrev table. Each buffer has a local abbrev table, but normally all buffers in the same major mode share one abbrev table. There is also a global abbrev table. Normally both are used.
An abbrev table is represented as an obarray containing a symbol for each abbreviation. The symbol's name is the abbreviation; its value is the expansion; its function definition is the hook function to do the expansion (see Defining Abbrevs); its property list cell contains the use count, the number of times the abbreviation has been expanded. Because these symbols are not interned in the usual obarray, they will never appear as the result of reading a Lisp expression; in fact, normally they are never used except by the code that handles abbrevs. Therefore, it is safe to use them in an extremely nonstandard way. See Creating Symbols.
For the user-level commands for abbrevs, see Abbrev Mode.
Abbrev mode is a minor mode controlled by the value of the variable
abbrev-mode.
A non-
nilvalue of this variable turns on the automatic expansion of abbrevs when their abbreviations are inserted into a buffer. If the value isnil, abbrevs may be defined, but they are not expanded automatically.This variable automatically becomes buffer-local when set in any fashion.
This is the value of
abbrev-modefor buffers that do not override it. This is the same as(default-value 'abbrev-mode).
This section describes how to create and manipulate abbrev tables.
This function creates and returns a new, empty abbrev table—an obarray containing no symbols. It is a vector filled with zeros.
This function undefines all the abbrevs in abbrev table table, leaving it empty. It always returns
nil.
This function defines tabname (a symbol) as an abbrev table name, i.e., as a variable whose value is an abbrev table. It defines abbrevs in the table according to definitions, a list of elements of the form
(abbrevname expansion hook usecount). The return value is alwaysnil.
This is a list of symbols whose values are abbrev tables.
define-abbrev-tableadds the new abbrev table name to this list.
This function inserts before point a description of the abbrev table named name. The argument name is a symbol whose value is an abbrev table. The return value is always
nil.If human is non-
nil, the description is human-oriented. Otherwise the description is a Lisp expression—a call todefine-abbrev-tablethat would define name exactly as it is currently defined.
These functions define an abbrev in a specified abbrev table.
define-abbrev is the low-level basic function, while
add-abbrev is used by commands that ask for information from the
user.
This function adds an abbreviation to abbrev table table based on information from the user. The argument type is a string describing in English the kind of abbrev this will be (typically,
"global"or"mode-specific"); this is used in prompting the user. The argument arg is the number of words in the expansion.The return value is the symbol that internally represents the new abbrev, or
nilif the user declines to confirm redefining an existing abbrev.
This function defines an abbrev named name, in table, to expand to expansion and call hook. The value of count, if specified, initializes the abbrev's usage-count. If count is not specified or
nil, the use count is initialized to zero. The return value is a symbol that represents the abbrev inside Emacs; its name is name.The argument name should be a string. The argument expansion is normally the desired expansion (a string), or
nilto undefine the abbrev. If it is anything but a string ornil, then the abbreviation “expands” solely by running hook.The argument hook is a function or
nil. If hook is non-nil, then it is called with no arguments after the abbrev is replaced with expansion; point is located at the end of expansion when hook is called.If hook is a non-nil symbol whose
no-self-insertproperty is non-nil, hook can explicitly control whether to insert the self-inserting input character that triggered the expansion. If hook returns non-nilin this case, that inhibits insertion of the character. By contrast, if hook returnsnil,expand-abbrevalso returnsnil, as if expansion had not really occurred.
If this variable is non-
nil, it means that the user plans to use global abbrevs only. This tells the commands that define mode-specific abbrevs to define global ones instead. This variable does not alter the behavior of the functions in this section; it is examined by their callers.
A file of saved abbrev definitions is actually a file of Lisp code.
The abbrevs are saved in the form of a Lisp program to define the same
abbrev tables with the same contents. Therefore, you can load the file
with load (see How Programs Do Loading). However, the
function quietly-read-abbrev-file is provided as a more
convenient interface.
User-level facilities such as save-some-buffers can save
abbrevs in a file automatically, under the control of variables
described here.
This function reads abbrev definitions from a file named filename, previously written with
write-abbrev-file. If filename is omitted ornil, the file specified inabbrev-file-nameis used.save-abbrevsis set totso that changes will be saved.This function does not display any messages. It returns
nil.
A non-
nilvalue forsave-abbrevmeans that Emacs should save abbrevs when files are saved.abbrev-file-namespecifies the file to save the abbrevs in.
This variable is set non-
nilby defining or altering any abbrevs. This serves as a flag for various Emacs commands to offer to save your abbrevs.
Save all abbrev definitions, in all abbrev tables, in the file filename, in the form of a Lisp program that when loaded will define the same abbrevs. If filename is
nilor omitted,abbrev-file-nameis used. This function returnsnil.
Abbrevs are usually expanded by certain interactive commands,
including self-insert-command. This section describes the
subroutines used in writing such commands, as well as the variables they
use for communication.
This function returns the symbol representing the abbrev named abbrev. The value returned is
nilif that abbrev is not defined. The optional second argument table is the abbrev table to look it up in. If table isnil, this function tries first the current buffer's local abbrev table, and second the global abbrev table.
This function returns the string that abbrev would expand into (as defined by the abbrev tables used for the current buffer). The optional argument table specifies the abbrev table to use, as in
abbrev-symbol.
This command expands the abbrev before point, if any. If point does not follow an abbrev, this command does nothing. The command returns the abbrev symbol if it did expansion,
nilotherwise.If the abbrev symbol has a hook function which is a symbol whose
no-self-insertproperty is non-nil, and if the hook function returnsnilas its value, thenexpand-abbrevreturnsnileven though expansion did occur.
Mark current point as the beginning of an abbrev. The next call to
expand-abbrevwill use the text from here to point (where it is then) as the abbrev to expand, rather than using the previous word as usual.
When this is set non-
nil, an abbrev entered entirely in upper case is expanded using all upper case. Otherwise, an abbrev entered entirely in upper case is expanded by capitalizing each word of the expansion.
This is the buffer position for
expand-abbrevto use as the start of the next abbrev to be expanded. (nilmeans use the word before point instead.)abbrev-start-locationis set tonileach timeexpand-abbrevis called. This variable is also set byabbrev-prefix-mark.
The value of this variable is the buffer for which
abbrev-start-locationhas been set. Trying to expand an abbrev in any other buffer clearsabbrev-start-location. This variable is set byabbrev-prefix-mark.
This is the
abbrev-symbolof the most recent abbrev expanded. This information is left byexpand-abbrevfor the sake of theunexpand-abbrevcommand (see Expanding Abbrevs).
This is the location of the most recent abbrev expanded. This contains information left by
expand-abbrevfor the sake of theunexpand-abbrevcommand.
This is the exact expansion text of the most recent abbrev expanded, after case conversion (if any). Its value is
nilif the abbrev has already been unexpanded. This contains information left byexpand-abbrevfor the sake of theunexpand-abbrevcommand.
This is a normal hook whose functions are executed, in sequence, just before any expansion of an abbrev. See Hooks. Since it is a normal hook, the hook functions receive no arguments. However, they can find the abbrev to be expanded by looking in the buffer before point. Running the hook is the first thing that
expand-abbrevdoes, and so a hook function can be used to change the current abbrev table before abbrev lookup happens.
The following sample code shows a simple use of
pre-abbrev-expand-hook. If the user terminates an abbrev with a
punctuation character, the hook function asks for confirmation. Thus,
this hook allows the user to decide whether to expand the abbrev, and
aborts expansion if it is not confirmed.
(add-hook 'pre-abbrev-expand-hook 'query-if-not-space)
;; This is the function invoked by pre-abbrev-expand-hook.
;; If the user terminated the abbrev with a space, the function does
;; nothing (that is, it returns so that the abbrev can expand). If the
;; user entered some other character, this function asks whether
;; expansion should continue.
;; If the user answers the prompt with y, the function returns
;; nil (because of the not function), but that is
;; acceptable; the return value has no effect on expansion.
(defun query-if-not-space ()
(if (/= ?\ (preceding-char))
(if (not (y-or-n-p "Do you want to expand this abbrev? "))
(error "Not expanding this abbrev"))))
Here we list the variables that hold the abbrev tables for the preloaded major modes of Emacs.
This is the abbrev table for mode-independent abbrevs. The abbrevs defined in it apply to all buffers. Each buffer may also have a local abbrev table, whose abbrev definitions take precedence over those in the global table.
The value of this buffer-local variable is the (mode-specific) abbreviation table of the current buffer.
This is the local abbrev table used in Fundamental mode; in other words, it is the local abbrev table in all buffers in Fundamental mode.
This is the local abbrev table used in Lisp mode and Emacs Lisp mode.
In the terminology of operating systems, a process is a space in which a program can execute. Emacs runs in a process. Emacs Lisp programs can invoke other programs in processes of their own. These are called subprocesses or child processes of the Emacs process, which is their parent process.
A subprocess of Emacs may be synchronous or asynchronous, depending on how it is created. When you create a synchronous subprocess, the Lisp program waits for the subprocess to terminate before continuing execution. When you create an asynchronous subprocess, it can run in parallel with the Lisp program. This kind of subprocess is represented within Emacs by a Lisp object which is also called a “process”. Lisp programs can use this object to communicate with the subprocess or to control it. For example, you can send signals, obtain status information, receive output from the process, or send input to it.
There are three functions that create a new subprocess in which to run
a program. One of them, start-process, creates an asynchronous
process and returns a process object (see Asynchronous Processes).
The other two, call-process and call-process-region,
create a synchronous process and do not return a process object
(see Synchronous Processes).
Synchronous and asynchronous processes are explained in the following sections. Since the three functions are all called in a similar fashion, their common arguments are described here.
In all cases, the function's program argument specifies the
program to be run. An error is signaled if the file is not found or
cannot be executed. If the file name is relative, the variable
exec-path contains a list of directories to search. Emacs
initializes exec-path when it starts up, based on the value of
the environment variable PATH. The standard file name
constructs, ‘~’, ‘.’, and ‘..’, are interpreted as usual
in exec-path, but environment variable substitutions
(‘$HOME’, etc.) are not recognized; use
substitute-in-file-name to perform them (see File Name Expansion).
Each of the subprocess-creating functions has a buffer-or-name
argument which specifies where the standard output from the program will
go. It should be a buffer or a buffer name; if it is a buffer name,
that will create the buffer if it does not already exist. It can also
be nil, which says to discard the output unless a filter function
handles it. (See Filter Functions, and Read and Print.)
Normally, you should avoid having multiple processes send output to the
same buffer because their output would be intermixed randomly.
All three of the subprocess-creating functions have a &rest
argument, args. The args must all be strings, and they are
supplied to program as separate command line arguments. Wildcard
characters and other shell constructs have no special meanings in these
strings, since the whole strings are passed directly to the specified
program.
Please note: The argument program contains only the name of the program; it may not contain any command-line arguments. You must use args to provide those.
The subprocess gets its current directory from the value of
default-directory (see File Name Expansion).
The subprocess inherits its environment from Emacs, but you can
specify overrides for it with process-environment. See System Environment.
The value of this variable is a string, the name of a directory that contains programs that come with GNU Emacs, programs intended for Emacs to invoke. The program
movemailis an example of such a program; Rmail uses it to fetch new mail from an inbox.
The value of this variable is a list of directories to search for programs to run in subprocesses. Each element is either the name of a directory (i.e., a string), or
nil, which stands for the default directory (which is the value ofdefault-directory). The value ofexec-pathis used bycall-processandstart-processwhen the program argument is not an absolute file name.
Lisp programs sometimes need to run a shell and give it a command
that contains file names that were specified by the user. These
programs ought to be able to support any valid file name. But the shell
gives special treatment to certain characters, and if these characters
occur in the file name, they will confuse the shell. To handle these
characters, use the function shell-quote-argument:
This function returns a string which represents, in shell syntax, an argument whose actual contents are argument. It should work reliably to concatenate the return value into a shell command and then pass it to a shell for execution.
Precisely what this function does depends on your operating system. The function is designed to work with the syntax of your system's standard shell; if you use an unusual shell, you will need to redefine this function.
;; This example shows the behavior on GNU and Unix systems. (shell-quote-argument "foo > bar") => "foo\\ \\>\\ bar" ;; This example shows the behavior on MS-DOS and MS-Windows systems. (shell-quote-argument "foo > bar") => "\"foo > bar\""Here's an example of using
shell-quote-argumentto construct a shell command:(concat "diff -c " (shell-quote-argument oldfile) " " (shell-quote-argument newfile))
After a synchronous process is created, Emacs waits for the
process to terminate before continuing. Starting Dired on GNU or
Unix9 is an example of this: it
runs ls in a synchronous process, then modifies the output
slightly. Because the process is synchronous, the entire directory
listing arrives in the buffer before Emacs tries to do anything with it.
While Emacs waits for the synchronous subprocess to terminate, the
user can quit by typing C-g. The first C-g tries to kill
the subprocess with a SIGINT signal; but it waits until the
subprocess actually terminates before quitting. If during that time the
user types another C-g, that kills the subprocess instantly with
SIGKILL and quits immediately (except on MS-DOS, where killing
other processes doesn't work). See Quitting.
The synchronous subprocess functions return an indication of how the process terminated.
The output from a synchronous subprocess is generally decoded using a
coding system, much like text read from a file. The input sent to a
subprocess by call-process-region is encoded using a coding
system, much like text written into a file. See Coding Systems.
This function calls program in a separate process and waits for it to finish.
The standard input for the process comes from file infile if infile is not
nil, and from the null device otherwise. The argument destination says where to put the process output. Here are the possibilities:
- a buffer
- Insert the output in that buffer, before point. This includes both the standard output stream and the standard error stream of the process.
- a string
- Insert the output in a buffer with that name, before point.
t- Insert the output in the current buffer, before point.
nil- Discard the output.
- 0
- Discard the output, and return
nilimmediately without waiting for the subprocess to finish.In this case, the process is not truly synchronous, since it can run in parallel with Emacs; but you can think of it as synchronous in that Emacs is essentially finished with the subprocess as soon as this function returns.
MS-DOS doesn't support asynchronous subprocesses, so this option doesn't work there.
(real-destination error-destination)- Keep the standard output stream separate from the standard error stream; deal with the ordinary output as specified by real-destination, and dispose of the error output according to error-destination. If error-destination is
nil, that means to discard the error output,tmeans mix it with the ordinary output, and a string specifies a file name to redirect error output into.You can't directly specify a buffer to put the error output in; that is too difficult to implement. But you can achieve this result by sending the error output to a temporary file and then inserting the file into a buffer.
If display is non-
nil, thencall-processredisplays the buffer as output is inserted. (However, if the coding system chosen for decoding output isundecided, meaning deduce the encoding from the actual data, then redisplay sometimes cannot continue once non-ascii characters are encountered. There are fundamental reasons why it is hard to fix this; see Output from Processes.)Otherwise the function
call-processdoes no redisplay, and the results become visible on the screen only when Emacs redisplays that buffer in the normal course of events.The remaining arguments, args, are strings that specify command line arguments for the program.
The value returned by
call-process(unless you told it not to wait) indicates the reason for process termination. A number gives the exit status of the subprocess; 0 means success, and any other value means failure. If the process terminated with a signal,call-processreturns a string describing the signal.In the examples below, the buffer ‘foo’ is current.
(call-process "pwd" nil t) => 0 ---------- Buffer: foo ---------- /usr/user/lewis/manual ---------- Buffer: foo ---------- (call-process "grep" nil "bar" nil "lewis" "/etc/passwd") => 0 ---------- Buffer: bar ---------- lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh ---------- Buffer: bar ----------Here is a good example of the use of
call-process, which used to be found in the definition ofinsert-directory:(call-process insert-directory-program nil t nil switches (if full-directory-p (concat (file-name-as-directory file) ".") file))
This function sends the text from start to end as standard input to a process running program. It deletes the text sent if delete is non-
nil; this is useful when destination ist, to insert the output in the current buffer in place of the input.The arguments destination and display control what to do with the output from the subprocess, and whether to update the display as it comes in. For details, see the description of
call-process, above. If destination is the integer 0,call-process-regiondiscards the output and returnsnilimmediately, without waiting for the subprocess to finish (this only works if asynchronous subprocesses are supported).The remaining arguments, args, are strings that specify command line arguments for the program.
The return value of
call-process-regionis just like that ofcall-process:nilif you told it to return without waiting; otherwise, a number or string which indicates how the subprocess terminated.In the following example, we use
call-process-regionto run thecatutility, with standard input being the first five characters in buffer ‘foo’ (the word ‘input’).catcopies its standard input into its standard output. Since the argument destination ist, this output is inserted in the current buffer.---------- Buffer: foo ---------- input-!- ---------- Buffer: foo ---------- (call-process-region 1 6 "cat" nil t) => 0 ---------- Buffer: foo ---------- inputinput-!- ---------- Buffer: foo ----------The
shell-command-on-regioncommand usescall-process-regionlike this:(call-process-region start end shell-file-name ; Name of program. nil ; Do not delete region. buffer ; Send output tobuffer. nil ; No redisplay during output. "-c" command) ; Arguments for the shell.
This function executes command (a string) as a shell command, then returns the command's output as a string.
After an asynchronous process is created, Emacs and the subprocess both continue running immediately. The process thereafter runs in parallel with Emacs, and the two can communicate with each other using the functions described in the following sections. However, communication is only partially asynchronous: Emacs sends data to the process only when certain functions are called, and Emacs accepts data from the process only when Emacs is waiting for input or for a time delay.
Here we describe how to create an asynchronous process.
This function creates a new asynchronous subprocess and starts the program program running in it. It returns a process object that stands for the new subprocess in Lisp. The argument name specifies the name for the process object; if a process with this name already exists, then name is modified (by appending ‘<1>’, etc.) to be unique. The buffer buffer-or-name is the buffer to associate with the process.
The remaining arguments, args, are strings that specify command line arguments for the program.
In the example below, the first process is started and runs (rather, sleeps) for 100 seconds. Meanwhile, the second process is started, and given the name ‘my-process<1>’ for the sake of uniqueness. It inserts the directory listing at the end of the buffer ‘foo’, before the first process finishes. Then it finishes, and a message to that effect is inserted in the buffer. Much later, the first process finishes, and another message is inserted in the buffer for it.
(start-process "my-process" "foo" "sleep" "100") => #<process my-process> (start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin") => #<process my-process<1>> ---------- Buffer: foo ---------- total 2 lrwxrwxrwx 1 lewis 14 Jul 22 10:12 gnuemacs --> /emacs -rwxrwxrwx 1 lewis 19 Jul 30 21:02 lemon Process my-process<1> finished Process my-process finished ---------- Buffer: foo ----------
This function is like
start-processexcept that it uses a shell to execute the specified command. The argument command is a shell command name, and command-args are the arguments for the shell command. The variableshell-file-namespecifies which shell to use.The point of running a program through the shell, rather than directly with
start-process, is so that you can employ shell features such as wildcards in the arguments. It follows that if you include an arbitrary user-specified arguments in the command, you should quote it withshell-quote-argumentfirst, so that any special shell characters do not have their special shell meanings. See Shell Arguments.
This variable controls the type of device used to communicate with asynchronous subprocesses. If it is non-
nil, then ptys are used, when available. Otherwise, pipes are used.ptys are usually preferable for processes visible to the user, as in Shell mode, because they allow job control (C-c, C-z, etc.) to work between the process and its children, whereas pipes do not. For subprocesses used for internal purposes by programs, it is often better to use a pipe, because they are more efficient. In addition, the total number of ptys is limited on many systems and it is good not to waste them.
The value of
process-connection-typeis used whenstart-processis called. So you can specify how to communicate with one subprocess by binding the variable around the call tostart-process.(let ((process-connection-type nil)) ; Use a pipe. (start-process ...))To determine whether a given subprocess actually got a pipe or a pty, use the function
process-tty-name(see Process Information).
Deleting a process disconnects Emacs immediately from the subprocess, and removes it from the list of active processes. It sends a signal to the subprocess to make the subprocess terminate, but this is not guaranteed to happen immediately. The process object itself continues to exist as long as other Lisp objects point to it. The process mark continues to point to the same place as before (usually into a buffer where output from the process was being inserted).
You can delete a process explicitly at any time. Processes are deleted automatically after they terminate, but not necessarily right away. If you delete a terminated process explicitly before it is deleted automatically, no harm results.
This variable controls automatic deletion of processes that have terminated (due to calling
exitor to a signal). If it isnil, then they continue to exist until the user runslist-processes. Otherwise, they are deleted immediately after they exit.
This function deletes the process associated with name, killing it with a
SIGHUPsignal. The argument name may be a process, the name of a process, a buffer, or the name of a buffer.(delete-process "*shell*") => nil
This function specifies whether Emacs should query the user if process is still running when Emacs is exited. If do-query is
nil, the process will be deleted silently. Otherwise, Emacs will query about killing it.The value is
tif the process was formerly set up to require query,nilotherwise. A newly-created process always requires query.(process-kill-without-query (get-process "shell")) => t
Several functions return information about processes.
list-processes is provided for interactive use.
This command displays a listing of all living processes. In addition, it finally deletes any process whose status was ‘Exited’ or ‘Signaled’. It returns
nil.
This function returns a list of all processes that have not been deleted.
(process-list) => (#<process display-time> #<process shell>)
This function returns the process named name, or
nilif there is none. An error is signaled if name is not a string.(get-process "shell") => #<process shell>
This function returns the command that was executed to start process. This is a list of strings, the first string being the program executed and the rest of the strings being the arguments that were given to the program.
(process-command (get-process "shell")) => ("/bin/csh" "-i")
This function returns the pid of process. This is an integer that distinguishes the process process from all other processes running on the same computer at the current time. The pid of a process is chosen by the operating system kernel when the process is started and remains constant as long as the process exists.
This function returns
tfor an ordinary child process, and(hostname service)for a net connection (see Network).
This function returns the status of process-name as a symbol. The argument process-name must be a process, a buffer, a process name (string) or a buffer name (string).
The possible values for an actual subprocess are:
run- for a process that is running.
stop- for a process that is stopped but continuable.
exit- for a process that has exited.
signal- for a process that has received a fatal signal.
open- for a network connection that is open.
closed- for a network connection that is closed. Once a connection is closed, you cannot reopen it, though you might be able to open a new connection to the same place.
nil- if process-name is not the name of an existing process.
(process-status "shell") => run (process-status (get-buffer "*shell*")) => run x => #<process xx<1>> (process-status x) => exitFor a network connection,
process-statusreturns one of the symbolsopenorclosed. The latter means that the other side closed the connection, or Emacs diddelete-process.
This function returns the exit status of process or the signal number that killed it. (Use the result of
process-statusto determine which of those it is.) If process has not yet terminated, the value is 0.
This function returns the terminal name that process is using for its communication with Emacs—or
nilif it is using pipes instead of a terminal (seeprocess-connection-typein Asynchronous Processes).
This function returns a cons cell describing the coding systems in use for decoding output from process and for encoding input to process (see Coding Systems). The value has this form:
(coding-system-for-decoding . coding-system-for-encoding)
This function specifies the coding systems to use for subsequent output from and input to process. It will use decoding-system to decode subprocess output, and encoding-system to encode subprocess input.
Asynchronous subprocesses receive input when it is sent to them by Emacs, which is done with the functions in this section. You must specify the process to send input to, and the input data to send. The data appears on the “standard input” of the subprocess.
Some operating systems have limited space for buffered input in a pty. On these systems, Emacs sends an eof periodically amidst the other characters, to force them through. For most programs, these eofs do no harm.
Subprocess input is normally encoded using a coding system before the
subprocess receives it, much like text written into a file. You can use
set-process-coding-system to specify which coding system to use
(see Process Information). Otherwise, the coding system comes from
coding-system-for-write, if that is non-nil; or else from
the defaulting mechanism (see Default Coding Systems).
Sometimes the system is unable to accept input for that process, because the input buffer is full. When this happens, the send functions wait a short while, accepting output from subprocesses, and then try again. This gives the subprocess a chance to read more of its pending input and make space in the buffer. It also allows filters, sentinels and timers to run—so take account of that in writing your code.
This function sends process-name the contents of string as standard input. The argument process-name must be a process or the name of a process. If it is
nil, the current buffer's process is used.The function returns
nil.(process-send-string "shell<1>" "ls\n") => nil ---------- Buffer: *shell* ---------- ... introduction.texi syntax-tables.texi~ introduction.texi~ text.texi introduction.txt text.texi~ ... ---------- Buffer: *shell* ----------
This function sends the text in the region defined by start and end as standard input to process-name, which is a process or a process name. (If it is
nil, the current buffer's process is used.)An error is signaled unless both start and end are integers or markers that indicate positions in the current buffer. (It is unimportant which number is larger.)
This function makes process-name see an end-of-file in its input. The eof comes after any text already sent to it.
If process-name is not supplied, or if it is
nil, then this function sends the eof to the current buffer's process. An error is signaled if the current buffer has no process.The function returns process-name.
(process-send-eof "shell") => "shell"
This function will tell you whether a subprocess has given control of its terminal to its own child process. The value is
tif this is true, or if Emacs cannot tell; it isnilif Emacs can be certain that this is not so.
Sending a signal to a subprocess is a way of interrupting its
activities. There are several different signals, each with its own
meaning. The set of signals and their names is defined by the operating
system. For example, the signal SIGINT means that the user has
typed C-c, or that some analogous thing has happened.
Each signal has a standard effect on the subprocess. Most signals kill the subprocess, but some stop or resume execution instead. Most signals can optionally be handled by programs; if the program handles the signal, then we can say nothing in general about its effects.
You can send signals explicitly by calling the functions in this
section. Emacs also sends signals automatically at certain times:
killing a buffer sends a SIGHUP signal to all its associated
processes; killing Emacs sends a SIGHUP signal to all remaining
processes. (SIGHUP is a signal that usually indicates that the
user hung up the phone.)
Each of the signal-sending functions takes two optional arguments: process-name and current-group.
The argument process-name must be either a process, the name of
one, or nil. If it is nil, the process defaults to the
process associated with the current buffer. An error is signaled if
process-name does not identify a process.
The argument current-group is a flag that makes a difference
when you are running a job-control shell as an Emacs subprocess. If it
is non-nil, then the signal is sent to the current process-group
of the terminal that Emacs uses to communicate with the subprocess. If
the process is a job-control shell, this means the shell's current
subjob. If it is nil, the signal is sent to the process group of
the immediate subprocess of Emacs. If the subprocess is a job-control
shell, this is the shell itself.
The flag current-group has no effect when a pipe is used to
communicate with the subprocess, because the operating system does not
support the distinction in the case of pipes. For the same reason,
job-control shells won't work when a pipe is used. See
process-connection-type in Asynchronous Processes.
This function interrupts the process process-name by sending the signal
SIGINT. Outside of Emacs, typing the “interrupt character” (normally C-c on some systems, andDELon others) sends this signal. When the argument current-group is non-nil, you can think of this function as “typing C-c” on the terminal by which Emacs talks to the subprocess.
This function kills the process process-name by sending the signal
SIGKILL. This signal kills the subprocess immediately, and cannot be handled by the subprocess.
This function sends the signal
SIGQUITto the process process-name. This signal is the one sent by the “quit character” (usually C-b or C-\) when you are not inside Emacs.
This function stops the process process-name by sending the signal
SIGTSTP. Usecontinue-processto resume its execution.Outside of Emacs, on systems with job control, the “stop character” (usually C-z) normally sends this signal. When current-group is non-
nil, you can think of this function as “typing C-z” on the terminal Emacs uses to communicate with the subprocess.
This function resumes execution of the process process by sending it the signal
SIGCONT. This presumes that process-name was stopped previously.
This function sends a signal to process pid, which need not be a child of Emacs. The argument signal specifies which signal to send; it should be an integer.
There are two ways to receive the output that a subprocess writes to its standard output stream. The output can be inserted in a buffer, which is called the associated buffer of the process, or a function called the filter function can be called to act on the output. If the process has no buffer and no filter function, its output is discarded.
Output from a subprocess can arrive only while Emacs is waiting: when
reading terminal input, in sit-for and sleep-for
(see Waiting), and in accept-process-output (see Accepting Output). This minimizes the problem of timing errors that usually
plague parallel programming. For example, you can safely create a
process and only then specify its buffer or filter function; no output
can arrive before you finish, if the code in between does not call any
primitive that waits.
It is impossible to separate the standard output and standard error streams of the subprocess, because Emacs normally spawns the subprocess inside a pseudo-TTY, and a pseudo-TTY has only one output channel. If you want to keep the output to those streams separate, you should redirect one of them to a file–for example, by using an appropriate shell command.
Subprocess output is normally decoded using a coding system before the
buffer or filter function receives it, much like text read from a file.
You can use set-process-coding-system to specify which coding
system to use (see Process Information). Otherwise, the coding
system comes from coding-system-for-read, if that is
non-nil; or else from the defaulting mechanism (see Default Coding Systems).
Warning: Coding systems such as undecided which
determine the coding system from the data do not work entirely reliably
with asynchronous subprocess output. This is because Emacs has to
process asynchronous subprocess output in batches, as it arrives. Emacs
must try to detect the proper coding system from one batch at a time,
and this does not always work. Therefore, if at all possible, use a
coding system which determines both the character code conversion and
the end of line conversion—that is, one like latin-1-unix,
rather than undecided or latin-1.
A process can (and usually does) have an associated buffer, which is an ordinary Emacs buffer that is used for two purposes: storing the output from the process, and deciding when to kill the process. You can also use the buffer to identify a process to operate on, since in normal practice only one process is associated with any given buffer. Many applications of processes also use the buffer for editing input to be sent to the process, but this is not built into Emacs Lisp.
Unless the process has a filter function (see Filter Functions),
its output is inserted in the associated buffer. The position to insert
the output is determined by the process-mark, which is then
updated to point to the end of the text just inserted. Usually, but not
always, the process-mark is at the end of the buffer.
This function returns the associated buffer of the process process.
(process-buffer (get-process "shell")) => #<buffer *shell*>
This function returns the process marker for process, which is the marker that says where to insert output from the process.
If process does not have a buffer,
process-markreturns a marker that points nowhere.Insertion of process output in a buffer uses this marker to decide where to insert, and updates it to point after the inserted text. That is why successive batches of output are inserted consecutively.
Filter functions normally should use this marker in the same fashion as is done by direct insertion of output in the buffer. A good example of a filter function that uses
process-markis found at the end of the following section.When the user is expected to enter input in the process buffer for transmission to the process, the process marker separates the new input from previous output.
This function sets the buffer associated with process to buffer. If buffer is
nil, the process becomes associated with no buffer.
This function returns the process associated with buffer-or-name. If there are several processes associated with it, then one is chosen. (Currently, the one chosen is the one most recently created.) It is usually a bad idea to have more than one process associated with the same buffer.
(get-buffer-process "*shell*") => #<process shell>Killing the process's buffer deletes the process, which kills the subprocess with a
SIGHUPsignal (see Signals to Processes).
A process filter function is a function that receives the standard output from the associated process. If a process has a filter, then all output from that process is passed to the filter. The process buffer is used directly for output from the process only when there is no filter.
The filter function can only be called when Emacs is waiting for
something, because process output arrives only at such times. Emacs
waits when reading terminal input, in sit-for and
sleep-for (see Waiting), and in accept-process-output
(see Accepting Output).
A filter function must accept two arguments: the associated process and a string, which is output just received from it. The function is then free to do whatever it chooses with the output.
Quitting is normally inhibited within a filter function—otherwise,
the effect of typing C-g at command level or to quit a user
command would be unpredictable. If you want to permit quitting inside a
filter function, bind inhibit-quit to nil.
See Quitting.
If an error happens during execution of a filter function, it is
caught automatically, so that it doesn't stop the execution of whatever
program was running when the filter function was started. However, if
debug-on-error is non-nil, the error-catching is turned
off. This makes it possible to use the Lisp debugger to debug the
filter function. See Debugger.
Many filter functions sometimes or always insert the text in the
process's buffer, mimicking the actions of Emacs when there is no
filter. Such filter functions need to use set-buffer in order to
be sure to insert in that buffer. To avoid setting the current buffer
semipermanently, these filter functions must save and restore the
current buffer. They should also update the process marker, and in some
cases update the value of point. Here is how to do these things:
(defun ordinary-insertion-filter (proc string)
(with-current-buffer (process-buffer proc)
(let ((moving (= (point) (process-mark proc))))
(save-excursion
;; Insert the text, advancing the process marker.
(goto-char (process-mark proc))
(insert string)
(set-marker (process-mark proc) (point)))
(if moving (goto-char (process-mark proc))))))
The reason to use with-current-buffer, rather than using
save-excursion to save and restore the current buffer, is so as
to preserve the change in point made by the second call to
goto-char.
To make the filter force the process buffer to be visible whenever new
text arrives, insert the following line just before the
with-current-buffer construct:
(display-buffer (process-buffer proc))
To force point to the end of the new output, no matter where it was
previously, eliminate the variable moving and call
goto-char unconditionally.
In earlier Emacs versions, every filter function that did regular expression searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically for filter functions; they never need to do it explicitly. See Match Data.
A filter function that writes the output into the buffer of the
process should check whether the buffer is still alive. If it tries to
insert into a dead buffer, it will get an error. The expression
(buffer-name (process-buffer process)) returns nil
if the buffer is dead.
The output to the function may come in chunks of any size. A program that produces the same output twice in a row may send it as one batch of 200 characters one time, and five batches of 40 characters the next. If the filter looks for certain text strings in the subprocess output, make sure to handle the case where one of these strings is split across two or more batches of output.
This function gives process the filter function filter. If filter is
nil, it gives the process no filter.
This function returns the filter function of process, or
nilif it has none.
Here is an example of use of a filter function:
(defun keep-output (process output)
(setq kept (cons output kept)))
=> keep-output
(setq kept nil)
=> nil
(set-process-filter (get-process "shell") 'keep-output)
=> keep-output
(process-send-string "shell" "ls ~/other\n")
=> nil
kept
=> ("lewis@slug[8] % "
"FINAL-W87-SHORT.MSS backup.otl kolstad.mss~
address.txt backup.psf kolstad.psf
backup.bib~ david.mss resume-Dec-86.mss~
backup.err david.psf resume-Dec.psf
backup.mss dland syllabus.mss
"
"#backups.mss# backup.mss~ kolstad.mss
")
Output from asynchronous subprocesses normally arrives only while Emacs is waiting for some sort of external event, such as elapsed time or terminal input. Occasionally it is useful in a Lisp program to explicitly permit output to arrive at a specific point, or even to wait until output arrives from a process.
This function allows Emacs to read pending output from processes. The output is inserted in the associated buffers or given to their filter functions. If process is non-
nilthen this function does not return until some output has been received from process.The arguments seconds and millisec let you specify timeout periods. The former specifies a period measured in seconds and the latter specifies one measured in milliseconds. The two time periods thus specified are added together, and
accept-process-outputreturns after that much time whether or not there has been any subprocess output.The argument seconds need not be an integer. If it is a floating point number, this function waits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down.
Not all operating systems support waiting periods other than multiples of a second; on those that do not, you get an error if you specify nonzero millisec.
The function
accept-process-outputreturns non-nilif it did get some output, ornilif the timeout expired before output arrived.
A process sentinel is a function that is called whenever the associated process changes status for any reason, including signals (whether sent by Emacs or caused by the process's own actions) that terminate, stop, or continue the process. The process sentinel is also called if the process exits. The sentinel receives two arguments: the process for which the event occurred, and a string describing the type of event.
The string describing the event looks like one of the following:
"finished\n".
"exited abnormally with code exitcode\n".
"name-of-signal\n".
"name-of-signal (core dumped)\n".
A sentinel runs only while Emacs is waiting (e.g., for terminal input,
or for time to elapse, or for process output). This avoids the timing
errors that could result from running them at random places in the
middle of other Lisp programs. A program can wait, so that sentinels
will run, by calling sit-for or sleep-for
(see Waiting), or accept-process-output (see Accepting Output). Emacs also allows sentinels to run when the command loop is
reading input.
Quitting is normally inhibited within a sentinel—otherwise, the
effect of typing C-g at command level or to quit a user command
would be unpredictable. If you want to permit quitting inside a
sentinel, bind inhibit-quit to nil. See Quitting.
A sentinel that writes the output into the buffer of the process
should check whether the buffer is still alive. If it tries to insert
into a dead buffer, it will get an error. If the buffer is dead,
(buffer-name (process-buffer process)) returns nil.
If an error happens during execution of a sentinel, it is caught
automatically, so that it doesn't stop the execution of whatever
programs was running when the sentinel was started. However, if
debug-on-error is non-nil, the error-catching is turned
off. This makes it possible to use the Lisp debugger to debug the
sentinel. See Debugger.
In earlier Emacs versions, every sentinel that did regular expression searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically for sentinels; they never need to do it explicitly. See Match Data.
This function associates sentinel with process. If sentinel is
nil, then the process will have no sentinel. The default behavior when there is no sentinel is to insert a message in the process's buffer when the process status changes.(defun msg-me (process event) (princ (format "Process: %s had the event `%s'" process event))) (set-process-sentinel (get-process "shell") 'msg-me) => msg-me (kill-process (get-process "shell")) -| Process: #<process shell> had the event `killed' => #<process shell>
This function returns the sentinel of process, or
nilif it has none.
While a sentinel or filter function is running, this function returns non-
nilif Emacs was waiting for keyboard input from the user at the time the sentinel or filter function was called,nilif it was not.
You can use a transaction queue to communicate with a subprocess
using transactions. First use tq-create to create a transaction
queue communicating with a specified process. Then you can call
tq-enqueue to send a transaction.
This function creates and returns a transaction queue communicating with process. The argument process should be a subprocess capable of sending and receiving streams of bytes. It may be a child process, or it may be a TCP connection to a server, possibly on another machine.
This function sends a transaction to queue queue. Specifying the queue has the effect of specifying the subprocess to talk to.
The argument question is the outgoing message that starts the transaction. The argument fn is the function to call when the corresponding answer comes back; it is called with two arguments: closure, and the answer received.
The argument regexp is a regular expression that should match text at the end of the entire answer, but nothing before; that's how
tq-enqueuedetermines where the answer ends.The return value of
tq-enqueueitself is not meaningful.
Shut down transaction queue queue, waiting for all pending transactions to complete, and then terminate the connection or child process.
Transaction queues are implemented by means of a filter function. See Filter Functions.
Emacs Lisp programs can open TCP network connections to other processes on
the same machine or other machines. A network connection is handled by Lisp
much like a subprocess, and is represented by a process object.
However, the process you are communicating with is not a child of the
Emacs process, so you can't kill it or send it signals. All you can do
is send and receive data. delete-process closes the connection,
but does not kill the process at the other end; that process must decide
what to do about closure of the connection.
You can distinguish process objects representing network connections
from those representing subprocesses with the process-status
function. It always returns either open or closed for a
network connection, and it never returns either of those values for a
real subprocess. See Process Information.
This function opens a TCP connection for a service to a host. It returns a process object to represent the connection.
The name argument specifies the name for the process object. It is modified as necessary to make it unique.
The buffer-or-name argument is the buffer to associate with the connection. Output from the connection is inserted in the buffer, unless you specify a filter function to handle the output. If buffer-or-name is
nil, it means that the connection is not associated with any buffer.The arguments host and service specify where to connect to; host is the host name (a string), and service is the name of a defined network service (a string) or a port number (an integer).
This chapter describes a number of features related to the display that Emacs presents to the user.
The function redraw-frame redisplays the entire contents of a
given frame (see Frames).
Even more powerful is redraw-display:
Processing user input takes absolute priority over redisplay. If you call these functions when input is available, they do nothing immediately, but a full redisplay does happen eventually—after all the input has been processed.
Normally, suspending and resuming Emacs also refreshes the screen. Some terminal emulators record separate contents for display-oriented programs such as Emacs and for ordinary sequential display. If you are using such a terminal, you might want to inhibit the redisplay on resumption.
This variable controls whether Emacs redraws the entire screen after it has been suspended and resumed. Non-
nilmeans there is no need to redraw,nilmeans redrawing is needed. The default isnil.
Emacs redisplay normally stops if input arrives, and does not happen
at all if input is available before it starts. Most of the time, this
is exactly what you want. However, you can prevent preemption by
binding redisplay-dont-pause to a non-nil value.
If this variable is non-
nil, pending input does not prevent or halt redisplay; redisplay occurs, and finishes, regardless of whether input is available. This feature is available as of Emacs 21.
You can request a display update, but only if no input is pending,
with (sit-for 0). To force a display update even when input is
pending, do this:
(let ((redisplay-dont-pause t))
(sit-for 0))
When a line of text extends beyond the right edge of a window, the line can either be continued on the next screen line, or truncated to one screen line. The additional screen lines used to display a long text line are called continuation lines. Normally, a ‘$’ in the rightmost column of the window indicates truncation; a ‘\’ on the rightmost column indicates a line that “wraps” onto the next line, which is also called continuing the line. (The display table can specify alternative indicators; see Display Tables.)
Note that continuation is different from filling; continuation happens on the screen only, not in the buffer contents, and it breaks a line precisely at the right margin, not at a word boundary. See Filling.
This buffer-local variable controls how Emacs displays lines that extend beyond the right edge of the window. The default is
nil, which specifies continuation. If the value is non-nil, then these lines are truncated.If the variable
truncate-partial-width-windowsis non-nil, then truncation is always used for side-by-side windows (within one frame) regardless of the value oftruncate-lines.
This variable is the default value for
truncate-lines, for buffers that do not have buffer-local values for it.
This variable controls display of lines that extend beyond the right edge of the window, in side-by-side windows (see Splitting Windows). If it is non-
nil, these lines are truncated; otherwise,truncate-linessays what to do with them.
When horizontal scrolling (see Horizontal Scrolling) is in use in a window, that forces truncation.
You can override the glyphs that indicate continuation or truncation using the display table; see Display Tables.
If your buffer contains very long lines, and you use
continuation to display them, just thinking about them can make Emacs
redisplay slow. The column computation and indentation functions also
become slow. Then you might find it advisable to set
cache-long-line-scans to t.
If this variable is non-
nil, various indentation and motion functions, and Emacs redisplay, cache the results of scanning the buffer, and consult the cache to avoid rescanning regions of the buffer unless they are modified.Turning on the cache slows down processing of short lines somewhat.
This variable is automatically buffer-local in every buffer.
The echo area is used for displaying messages made with the
message primitive, and for echoing keystrokes. It is not the
same as the minibuffer, despite the fact that the minibuffer appears
(when active) in the same place on the screen as the echo area. The
GNU Emacs Manual specifies the rules for resolving conflicts
between the echo area and the minibuffer for use of that screen space
(see The Minibuffer).
Error messages appear in the echo area; see Errors.
You can write output in the echo area by using the Lisp printing
functions with t as the stream (see Output Functions), or as
follows:
This function displays a message in the echo area. The argument string is similar to a C language
printfcontrol string. Seeformatin String Conversion, for the details on the conversion specifications.messagereturns the constructed string.In batch mode,
messageprints the message text on the standard error stream, followed by a newline.If string, or strings among the arguments, have
facetext properties, these affect the way the message is displayed.If string is
nil,messageclears the echo area; if the echo area has been expanded automatically, this brings it back to its normal size. If the minibuffer is active, this brings the minibuffer contents back onto the screen immediately.Normally, displaying a long message resizes the echo area to display the entire message. But if the variable
message-truncate-linesis non-nil, the echo area does not resize, and the message is truncated to fit it, as in Emacs 20 and before.(message "Minibuffer depth is %d." (minibuffer-depth)) -| Minibuffer depth is 0. => "Minibuffer depth is 0." ---------- Echo Area ---------- Minibuffer depth is 0. ---------- Echo Area ----------To automatically display a message in the echo area or in a pop-buffer, depending on its size, use
display-message-or-buffer.
This construct displays a message in the echo area temporarily, during the execution of body. It displays message, executes body, then returns the value of the last body form while restoring the previous echo area contents.
This function displays a message like
message, but may display it in a dialog box instead of the echo area. If this function is called in a command that was invoked using the mouse—more precisely, iflast-nonmenu-event(see Command Loop Info) is eithernilor a list—then it uses a dialog box or pop-up menu to display the message. Otherwise, it uses the echo area. (This is the same criterion thaty-or-n-puses to make a similar decision; see Yes-or-No Queries.)You can force use of the mouse or of the echo area by binding
last-nonmenu-eventto a suitable value around the call.
This function displays a message like
message, but uses a dialog box (or a pop-up menu) whenever that is possible. If it is impossible to use a dialog box or pop-up menu, because the terminal does not support them, thenmessage-boxuses the echo area, likemessage.
This function displays the message message, which may be either a string or a buffer. If it is shorter than the maximum height of the echo area, as defined by
max-mini-window-height, it is displayed in the echo area, usingmessage. Otherwise,display-bufferis used to show it in a pop-up buffer.Returns either the string shown in the echo area, or when a pop-up buffer is used, the window used to display it.
If message is a string, then the optional argument buffer-name is the name of the buffer used to display it when a pop-up buffer is used, defaulting to ‘*Message*’. In the case where message is a string and displayed in the echo area, it is not specified whether the contents are inserted into the buffer anyway.
The optional arguments not-this-window and frame are as for
display-buffer, and only used if a buffer is displayed.
This function returns the message currently being displayed in the echo area, or
nilif there is none.
This variable controls where the cursor appears when a message is displayed in the echo area. If it is non-
nil, then the cursor appears at the end of the message. Otherwise, the cursor appears at point—not in the echo area at all.The value is normally
nil; Lisp programs bind it totfor brief periods of time.
This normal hook is run whenever the echo area is cleared—either by
(message nil)or for any other reason.
Almost all the messages displayed in the echo area are also recorded in the ‘*Messages*’ buffer.
This variable specifies how many lines to keep in the ‘*Messages*’ buffer. The value
tmeans there is no limit on how many lines to keep. The valuenildisables message logging entirely. Here's how to display a message and prevent it from being logged:(let (message-log-max) (message ...))
This variable determines how much time should elapse before command characters echo. Its value must be an integer or floating point number, which specifies the number of seconds to wait before echoing. If the user types a prefix key (such as C-x) and then delays this many seconds before continuing, the prefix key is echoed in the echo area. (Once echoing begins in a key sequence, all subsequent characters in the same key sequence are echoed immediately.)
If the value is zero, then command input is not echoed.
You can make characters invisible, so that they do not appear on
the screen, with the invisible property. This can be either a
text property (see Text Properties) or a property of an overlay
(see Overlays).
In the simplest case, any non-nil invisible property makes
a character invisible. This is the default case—if you don't alter
the default value of buffer-invisibility-spec, this is how the
invisible property works.
More generally, you can use the variable buffer-invisibility-spec
to control which values of the invisible property make text
invisible. This permits you to classify the text into different subsets
in advance, by giving them different invisible values, and
subsequently make various subsets visible or invisible by changing the
value of buffer-invisibility-spec.
Controlling visibility with buffer-invisibility-spec is
especially useful in a program to display the list of entries in a
database. It permits the implementation of convenient filtering
commands to view just a part of the entries in the database. Setting
this variable is very fast, much faster than scanning all the text in
the buffer looking for properties to change.
This variable specifies which kinds of
invisibleproperties actually make a character invisible.
t- A character is invisible if its
invisibleproperty is non-nil. This is the default.- a list
- Each element of the list specifies a criterion for invisibility; if a character's
invisibleproperty fits any one of these criteria, the character is invisible. The list can have two kinds of elements:
- atom
- A character is invisible if its
invisibleproperty value is atom or if it is a list with atom as a member.(atom. t)- A character is invisible if its
invisibleproperty value is atom or if it is a list with atom as a member. Moreover, if this character is at the end of a line and is followed by a visible newline, it displays an ellipsis.
Two functions are specifically provided for adding elements to
buffer-invisibility-spec and removing elements from it.
Add the element element to
buffer-invisibility-spec(if it is not already present in that list).
Remove the element element from
buffer-invisibility-spec. This does nothing if element is not in the list.
One convention about the use of buffer-invisibility-spec is
that a major mode should use the mode's own name as an element of
buffer-invisibility-spec and as the value of the invisible
property:
;; If you want to display an ellipsis: (add-to-invisibility-spec '(my-symbol . t)) ;; If you don't want ellipsis: (add-to-invisibility-spec 'my-symbol) (overlay-put (make-overlay beginning end) 'invisible 'my-symbol) ;; When done with the overlays: (remove-from-invisibility-spec '(my-symbol . t)) ;; Or respectively: (remove-from-invisibility-spec 'my-symbol)
Ordinarily, commands that operate on text or move point do not care
whether the text is invisible. The user-level line motion commands
explicitly ignore invisible newlines if
line-move-ignore-invisible is non-nil, but only because
they are explicitly programmed to do so.
Incremental search can make invisible overlays visible temporarily
and/or permanently when a match includes invisible text. To enable
this, the overlay should have a non-nil
isearch-open-invisible property. The property value should be a
function to be called with the overlay as an argument. This function
should make the overlay visible permanently; it is used when the match
overlaps the overlay on exit from the search.
During the search, such overlays are made temporarily visible by
temporarily modifying their invisible and intangible properties. If you
want this to be done differently for a certain overlay, give it an
isearch-open-invisible-temporary property which is a function.
The function is called with two arguments: the first is the overlay, and
the second is nil to make the overlay visible, or t to
make it invisible again.
Selective display refers to a pair of related features for hiding certain lines on the screen.
The first variant, explicit selective display, is designed for use in a Lisp program: it controls which lines are hidden by altering the text. The invisible text feature (see Invisible Text) has partially replaced this feature.
In the second variant, the choice of lines to hide is made automatically based on indentation. This variant is designed to be a user-level feature.
The way you control explicit selective display is by replacing a newline (control-j) with a carriage return (control-m). The text that was formerly a line following that newline is now invisible. Strictly speaking, it is temporarily no longer a line at all, since only newlines can separate lines; it is now part of the previous line.
Selective display does not directly affect editing commands. For
example, C-f (forward-char) moves point unhesitatingly into
invisible text. However, the replacement of newline characters with
carriage return characters affects some editing commands. For example,
next-line skips invisible lines, since it searches only for
newlines. Modes that use selective display can also define commands
that take account of the newlines, or that make parts of the text
visible or invisible.
When you write a selectively displayed buffer into a file, all the control-m's are output as newlines. This means that when you next read in the file, it looks OK, with nothing invisible. The selective display effect is seen only within Emacs.
This buffer-local variable enables selective display. This means that lines, or portions of lines, may be made invisible.
- If the value of
selective-displayist, then the character control-m marks the start of invisible text; the control-m, and the rest of the line following it, are not displayed. This is explicit selective display.- If the value of
selective-displayis a positive integer, then lines that start with more than that many columns of indentation are not displayed.When some portion of a buffer is invisible, the vertical movement commands operate as if that portion did not exist, allowing a single
next-linecommand to skip any number of invisible lines. However, character movement commands (such asforward-char) do not skip the invisible portion, and it is possible (if tricky) to insert or delete text in an invisible portion.In the examples below, we show the display appearance of the buffer
foo, which changes with the value ofselective-display. The contents of the buffer do not change.(setq selective-display nil) => nil ---------- Buffer: foo ---------- 1 on this column 2on this column 3n this column 3n this column 2on this column 1 on this column ---------- Buffer: foo ---------- (setq selective-display 2) => 2 ---------- Buffer: foo ---------- 1 on this column 2on this column 2on this column 1 on this column ---------- Buffer: foo ----------
If this buffer-local variable is non-
nil, then Emacs displays ‘...’ at the end of a line that is followed by invisible text. This example is a continuation of the previous one.(setq selective-display-ellipses t) => t ---------- Buffer: foo ---------- 1 on this column 2on this column ... 2on this column 1 on this column ---------- Buffer: foo ----------You can use a display table to substitute other text for the ellipsis (‘...’). See Display Tables.
The overlay arrow is useful for directing the user's attention to a particular line in a buffer. For example, in the modes used for interface to debuggers, the overlay arrow indicates the line of code about to be executed.
This variable holds the string to display to call attention to a particular line, or
nilif the arrow feature is not in use. On a graphical display the contents of the string are ignored; instead a glyph is displayed in the fringe area to the left of the display area.
This variable holds a marker that indicates where to display the overlay arrow. It should point at the beginning of a line. On a non-graphical display the arrow text appears at the beginning of that line, overlaying any text that would otherwise appear. Since the arrow is usually short, and the line usually begins with indentation, normally nothing significant is overwritten.
The overlay string is displayed only in the buffer that this marker points into. Thus, only one buffer can have an overlay arrow at any given time.
You can do a similar job by creating an overlay with a
before-string property. See Overlay Properties.
Temporary displays are used by Lisp programs to put output into a buffer and then present it to the user for perusal rather than for editing. Many help commands use this feature.
This function executes forms while arranging to insert any output they print into the buffer named buffer-name, which is first created if necessary, and put into Help mode. Finally, the buffer is displayed in some window, but not selected.
If the forms do not change the major mode in the output buffer, so that it is still Help mode at the end of their execution, then
with-output-to-temp-buffermakes this buffer read-only at the end, and also scans it for function and variable names to make them into clickable cross-references.The string buffer-name specifies the temporary buffer, which need not already exist. The argument must be a string, not a buffer. The buffer is erased initially (with no questions asked), and it is marked as unmodified after
with-output-to-temp-bufferexits.
with-output-to-temp-bufferbindsstandard-outputto the temporary buffer, then it evaluates the forms in forms. Output using the Lisp output functions within forms goes by default to that buffer (but screen display and messages in the echo area, although they are “output” in the general sense of the word, are not affected). See Output Functions.Several hooks are available for customizing the behavior of this construct; they are listed below.
The value of the last form in forms is returned.
---------- Buffer: foo ---------- This is the contents of foo. ---------- Buffer: foo ---------- (with-output-to-temp-buffer "foo" (print 20) (print standard-output)) => #<buffer foo> ---------- Buffer: foo ---------- 20 #<buffer foo> ---------- Buffer: foo ----------
If this variable is non-
nil,with-output-to-temp-buffercalls it as a function to do the job of displaying a help buffer. The function gets one argument, which is the buffer it should display.It is a good idea for this function to run
temp-buffer-show-hookjust aswith-output-to-temp-buffernormally would, inside ofsave-selected-windowand with the chosen window and buffer selected.
This normal hook is run by
with-output-to-temp-bufferbefore evaluating body. When the hook runs, the help buffer is current. This hook is normally set up with a function to put the buffer in Help mode.
This normal hook is run by
with-output-to-temp-bufferafter displaying the help buffer. When the hook runs, the help buffer is current, and the window it was displayed in is selected. This hook is normally set up with a function to make the buffer read only, and find function names and variable names in it, provided the major mode is still Help mode.
This function momentarily displays string in the current buffer at position. It has no effect on the undo list or on the buffer's modification status.
The momentary display remains until the next input event. If the next input event is char,
momentary-string-displayignores it and returns. Otherwise, that event remains buffered for subsequent use as input. Thus, typing char will simply remove the string from the display, while typing (say) C-f will remove the string from the display and later (presumably) move point forward. The argument char is a space by default.The return value of
momentary-string-displayis not meaningful.If the string string does not contain control characters, you can do the same job in a more general way by creating (and then subsequently deleting) an overlay with a
before-stringproperty. See Overlay Properties.If message is non-
nil, it is displayed in the echo area while string is displayed in the buffer. If it isnil, a default message says to type char to continue.In this example, point is initially located at the beginning of the second line:
---------- Buffer: foo ---------- This is the contents of foo. -!-Second line. ---------- Buffer: foo ---------- (momentary-string-display "**** Important Message! ****" (point) ?\r "Type RET when done reading") => t ---------- Buffer: foo ---------- This is the contents of foo. **** Important Message! ****Second line. ---------- Buffer: foo ---------- ---------- Echo Area ---------- Type RET when done reading ---------- Echo Area ----------
You can use overlays to alter the appearance of a buffer's text on the screen, for the sake of presentation features. An overlay is an object that belongs to a particular buffer, and has a specified beginning and end. It also has properties that you can examine and set; these affect the display of the text within the overlay.
Overlay properties are like text properties in that the properties that alter how a character is displayed can come from either source. But in most respects they are different. Text properties are considered a part of the text; overlays are specifically considered not to be part of the text. Thus, copying text between various buffers and strings preserves text properties, but does not try to preserve overlays. Changing a buffer's text properties marks the buffer as modified, while moving an overlay or changing its properties does not. Unlike text property changes, overlay changes are not recorded in the buffer's undo list. See Text Properties, for comparison.
These functions are used for reading and writing the properties of an overlay:
This function returns the value of property prop recorded in overlay, if any. If overlay does not record any value for that property, but it does have a
categoryproperty which is a symbol, that symbol's prop property is used. Otherwise, the value isnil.
This function sets the value of property prop recorded in overlay to value. It returns value.
See also the function get-char-property which checks both
overlay properties and text properties for a given character.
See Examining Properties.
Many overlay properties have special meanings; here is a table of them:
prioritypriority value is larger takes priority over the
other, and its face attributes override the face attributes of the lower
priority overlay.
Currently, all overlays take priority over text properties. Please
avoid using negative priority values, as we have not yet decided just
what they should mean.
windowwindow property is non-nil, then the overlay
applies only on that window.
categorycategory property, we call it the
category of the overlay. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the overlay.
faceIn the simplest case, the value is a face name. It can also be a list; then each element can be any of these possibilities:
(foreground-color . color-name) or
(background-color . color-name). These elements specify
just the foreground color or just the background color.
(foreground-color . color-name) is equivalent to
(:foreground color-name), and likewise for the background.
mouse-faceface when the mouse is within
the range of the overlay.
displayhelp-echohelp-echo property, then when you move the
mouse onto the text in the overlay, Emacs displays a help string in the
echo area, or in the tooltip window. For details see Text help-echo. This feature is available starting in Emacs 21.
modification-hooksThe hook functions are called both before and after each change. If the functions save the information they receive, and compare notes between calls, they can determine exactly what change has been made in the buffer text.
When called before a change, each function receives four arguments: the
overlay, nil, and the beginning and end of the text range to be
modified.
When called after a change, each function receives five arguments: the
overlay, t, the beginning and end of the text range just
modified, and the length of the pre-change text replaced by that range.
(For an insertion, the pre-change length is zero; for a deletion, that
length is the number of characters deleted, and the post-change
beginning and end are equal.)
insert-in-front-hooksmodification-hooks functions.
insert-behind-hooksmodification-hooks functions.
invisibleinvisible property can make the text in the overlay
invisible, which means that it does not appear on the screen.
See Invisible Text, for details.
intangibleintangible property on an overlay works just like the
intangible text property. See Special Properties, for details.
isearch-open-invisibleisearch-open-invisible-temporarybefore-stringafter-stringevaporatenil, the overlay is deleted automatically
if it ever becomes empty (i.e., if it spans no characters).
local-mapnil, it specifies a keymap for a portion
of the text. The property's value replaces the buffer's local map, when
the character after point is within the overlay. See Active Keymaps.
keymapkeymap property is similar to local-map but overrides the
buffer's local map (and the map specified by the local-map
property) rather than replacing it.
This section describes the functions to create, delete and move overlays, and to examine their contents.
This function creates and returns an overlay that belongs to buffer and ranges from start to end. Both start and end must specify buffer positions; they may be integers or markers. If buffer is omitted, the overlay is created in the current buffer.
The arguments front-advance and rear-advance specify the insertion type for the start of the overlay and for the end of the overlay, respectively. See Marker Insertion Types.
This function returns the position at which overlay starts, as an integer.
This function returns the position at which overlay ends, as an integer.
This function deletes overlay. The overlay continues to exist as a Lisp object, and its property list is unchanged, but it ceases to be attached to the buffer it belonged to, and ceases to have any effect on display.
A deleted overlay is not permanently disconnected. You can give it a position in a buffer again by calling
move-overlay.
This function moves overlay to buffer, and places its bounds at start and end. Both arguments start and end must specify buffer positions; they may be integers or markers.
If buffer is omitted, overlay stays in the same buffer it was already associated with; if overlay was deleted, it goes into the current buffer.
The return value is overlay.
This is the only valid way to change the endpoints of an overlay. Do not try modifying the markers in the overlay by hand, as that fails to update other vital data structures and can cause some overlays to be “lost”.
Here are some examples:
;; Create an overlay. (setq foo (make-overlay 1 10)) => #<overlay from 1 to 10 in display.texi> (overlay-start foo) => 1 (overlay-end foo) => 10 (overlay-buffer foo) => #<buffer display.texi> ;; Give it a property we can check later. (overlay-put foo 'happy t) => t ;; Verify the property is present. (overlay-get foo 'happy) => t ;; Move the overlay. (move-overlay foo 5 20) => #<overlay from 5 to 20 in display.texi> (overlay-start foo) => 5 (overlay-end foo) => 20 ;; Delete the overlay. (delete-overlay foo) => nil ;; Verify it is deleted. foo => #<overlay in no buffer> ;; A deleted overlay has no position. (overlay-start foo) => nil (overlay-end foo) => nil (overlay-buffer foo) => nil ;; Undelete the overlay. (move-overlay foo 1 20) => #<overlay from 1 to 20 in display.texi> ;; Verify the results. (overlay-start foo) => 1 (overlay-end foo) => 20 (overlay-buffer foo) => #<buffer display.texi> ;; Moving and deleting the overlay does not change its properties. (overlay-get foo 'happy) => t
This function returns a list of all the overlays that cover the character at position pos in the current buffer. The list is in no particular order. An overlay contains position pos if it begins at or before pos, and ends after pos.
To illustrate usage, here is a Lisp function that returns a list of the overlays that specify property prop for the character at point:
(defun find-overlays-specifying (prop) (let ((overlays (overlays-at (point))) found) (while overlays (let ((overlay (car overlays))) (if (overlay-get overlay prop) (setq found (cons overlay found)))) (setq overlays (cdr overlays))) found))
This function returns a list of the overlays that overlap the region beg through end. “Overlap” means that at least one character is contained within the overlay and also contained within the specified region; however, empty overlays are included in the result if they are located at beg, or strictly between beg and end.
This function returns the buffer position of the next beginning or end of an overlay, after pos.
This function returns the buffer position of the previous beginning or end of an overlay, before pos.
Here's an easy way to use next-overlay-change to search for the
next character which gets a non-nil happy property from
either its overlays or its text properties (see Property Search):
(defun find-overlay-prop (prop)
(save-excursion
(while (and (not (eobp))
(not (get-char-property (point) 'happy)))
(goto-char (min (next-overlay-change (point))
(next-single-property-change (point) 'happy))))
(point)))
Since not all characters have the same width, these functions let you check the width of a character. See Primitive Indent, and Screen Lines, for related functions.
This function returns the width in columns of the character char, if it were displayed in the current buffer and the selected window.
This function returns the width in columns of the string string, if it were displayed in the current buffer and the selected window.
This function returns the part of string that fits within width columns, as a new string.
If string does not reach width, then the result ends where string ends. If one multi-column character in string extends across the column width, that character is not included in the result. Thus, the result can fall short of width but cannot go beyond it.
The optional argument start-column specifies the starting column. If this is non-
nil, then the first start-column columns of the string are omitted from the value. If one multi-column character in string extends across the column start-column, that character is not included.The optional argument padding, if non-
nil, is a padding character added at the beginning and end of the result string, to extend it to exactly width columns. The padding character is used at the end of the result if it falls short of width. It is also used at the beginning of the result if one multi-column character in string extends across the column start-column.(truncate-string-to-width "\tab\t" 12 4) => "ab" (truncate-string-to-width "\tab\t" 12 4 ?\ ) => " ab "
A face is a named collection of graphical attributes: font family, foreground color, background color, optional underlining, and many others. Faces are used in Emacs to control the style of display of particular parts of the text or the frame.
Each face has its own face number, which distinguishes faces at low levels within Emacs. However, for most purposes, you refer to faces in Lisp programs by their names.
This function returns
tif object is a face name symbol (or if it is a vector of the kind used internally to record face data). It returnsnilotherwise.
Each face name is meaningful for all frames, and by default it has the same meaning in all frames. But you can arrange to give a particular face name a special meaning in one frame if you wish.
This table lists all the standard faces and their uses. Most of them are used for displaying certain parts of the frames or certain kinds of text; you can control how those places look by customizing these faces.
defaultmode-linemode-line-inverse-video is
non-nil.
modelinemode-line face, for compatibility with
old Emacs versions.
header-linemenufringescroll-bartool-barregionsecondary-selectionhighlighttrailing-whitespaceshow-trailing-whitespace is non-nil.
In contrast, these faces are provided to change the appearance of text in specific ways. You can use them on specific text, when you want the effects they produce.
bolditalicbold-italicunderlinefixed-pitchvariable-pitchIf this variable is non-
nil, Emacs uses thetrailing-whitespaceface to display any spaces and tabs at the end of a line.
The way to define a new face is with defface. This creates a
kind of customization item (see Customization) which the user can
customize using the Customization buffer (see Easy Customization).
This declares face as a customizable face that defaults according to spec. You should not quote the symbol face. The argument doc specifies the face documentation. The keywords you can use in
deffaceare the same ones that are meaningful in bothdefgroupanddefcustom(see Common Keywords).When
deffaceexecutes, it defines the face according to spec, then uses any customizations that were read from the init file (see Init File) to override that specification.The purpose of spec is to specify how the face should appear on different kinds of terminals. It should be an alist whose elements have the form
(display atts). Each element's car, display, specifies a class of terminals. The element's second element, atts, is a list of face attributes and their values; it specifies what the face should look like on that kind of terminal. The possible attributes are defined in the value ofcustom-face-attributes.The display part of an element of spec determines which frames the element applies to. If more than one element of spec matches a given frame, the first matching element is the only one used for that frame. There are two possibilities for display:
t- This element of spec matches all frames. Therefore, any subsequent elements of spec are never used. Normally
tis used in the last (or only) element of spec.- a list
- If display is a list, each element should have the form
(characteristic value...). Here characteristic specifies a way of classifying frames, and the values are possible classifications which display should apply to. Here are the possible values of characteristic:
type- The kind of window system the frame uses—either
graphic(any graphics-capable display),x,pc(for the MS-DOS console),w32(for MS Windows 9X/NT), ortty(a non-graphics-capable display).class- What kinds of colors the frame supports—either
color,grayscale, ormono.background- The kind of background—either
lightordark.If an element of display specifies more than one value for a given characteristic, any of those values is acceptable. If display has more than one element, each element should specify a different characteristic; then each characteristic of the frame must match one of the values specified for it in display.
Here's how the standard face region is defined:
(defface region
`((((type tty) (class color))
(:background "blue" :foreground "white"))
(((type tty) (class mono))
(:inverse-video t))
(((class color) (background dark))
(:background "blue"))
(((class color) (background light))
(:background "lightblue"))
(t (:background "gray")))
"Basic face for highlighting the region."
:group 'basic-faces)
Internally, defface uses the symbol property
face-defface-spec to record the face attributes specified in
defface, saved-face for the attributes saved by the user
with the customization buffer, and face-documentation for the
documentation string.
This option, if non-
nil, specifies the background type to use for interpreting face definitions. If it isdark, then Emacs treats all frames as if they had a dark background, regardless of their actual background colors. If it islight, then Emacs treats all frames as if they had a light background.
The effect of using a face is determined by a fixed set of face attributes. This table lists all the face attributes, and what they mean. Note that in general, more than one face can be specified for a given piece of text; when that happens, the attributes of all the faces are merged to specify how to display the text. See Merging Faces.
In Emacs 21, any attribute in a face can have the value
unspecified. This means the face doesn't specify that attribute.
In face merging, when the first face fails to specify a particular
attribute, that means the next face gets a chance. However, the
default face must specify all attributes.
Some of these font attributes are meaningful only on certain kinds of
displays—if your display cannot handle a certain attribute, the
attribute is ignored. (The attributes :family, :width,
:height, :weight, and :slant correspond to parts of
an X Logical Font Descriptor.)
:family:widthultra-condensed,
extra-condensed, condensed, semi-condensed,
normal, semi-expanded, expanded,
extra-expanded, or ultra-expanded.
:height:weightultra-bold, extra-bold, bold, semi-bold,
normal, semi-light, light, extra-light,
or ultra-light.
On a text-only terminal, any weight greater than normal is displayed as
extra bright, and any weight less than normal is displayed as
half-bright (provided the terminal supports the feature).
:slantitalic, oblique, normal,
reverse-italic, or reverse-oblique.
On a text-only terminal, slanted text is displayed as half-bright, if
the terminal supports the feature.
:foreground:background:inverse-videot (yes) or nil (no).
:stippleThe value can be a string; that should be the name of a file containing
external-format X bitmap data. The file is found in the directories
listed in the variable x-bitmap-file-path.
Alternatively, the value can specify the bitmap directly, with a list of
the form (width height data). Here,
width and height specify the size in pixels, and data
is a string containing the raw bits of the bitmap, row by row. Each row
occupies (width + 7) / 8 consecutie bytes in the string
(which should be a unibyte string for best results).
If the value is nil, that means use no stipple pattern.
Normally you do not need to set the stipple attribute, because it is
used automatically to handle certain shades of gray.
:underlinet, underlining uses the foreground color of the
face. If the value is a string, underlining uses that color. The
value nil means do not underline.
:overline:underline.
:strike-through:underline.
:inherit:boxHere are the possible values of the :box attribute, and what
they mean:
nilt(:line-width width :color color :style style)The value color specifies the color to draw with. The default is the foreground color of the face for simple boxes, and the background color of the face for 3D boxes.
The value style specifies whether to draw a 3D box. If it is
released-button, the box looks like a 3D button that is not being
pressed. If it is pressed-button, the box looks like a 3D button
that is being pressed. If it is nil or omitted, a plain 2D box
is used.
The attributes :overline, :strike-through and
:box are new in Emacs 21. The attributes :family,
:height, :width, :weight, :slant are also
new; previous versions used the following attributes, now semi-obsolete,
to specify some of the same information:
:font:boldnil value specifies a bold font.
:italicnil value specifies an italic font.
For compatibility, you can still set these “attributes” in Emacs 21, even though they are not real face attributes. Here is what that does:
:font:family, :width, :height,
:weight, and :slant attributes according to the font name.
If the value is a pattern with wildcards, the first font that matches
the pattern is used to set these attributes.
:boldnil makes the face bold; nil makes it normal.
This actually works by setting the :weight attribute.
:italicnil makes the face italic; nil makes it normal.
This actually works by setting the :slant attribute.
This variable specifies a list of directories for searching for bitmap files, for the
:stippleattribute.
This returns
tif object is a valid bitmap specification, suitable for use with:stipple. It returnsnilotherwise.
You can modify the attributes of an existing face with the following functions. If you specify frame, they affect just that frame; otherwise, they affect all frames as well as the defaults that apply to new frames.
This function sets one or more attributes of face face for frame frame. If frame is
nil, it sets the attribute for all frames, and the defaults for new frames.The extra arguments arguments specify the attributes to set, and the values for them. They should consist of alternating attribute names (such as
:familyor:underline) and corresponding values. Thus,(set-face-attribute 'foo nil :width :extended :weight :bold :underline "red")sets the attributes
:width,:weightand:underlineto the corresponding values.
This returns the value of the attribute attribute of face face on frame. If frame is
nil, that means the selected frame (see Input Focus).If frame is
t, the value is the default for face for new frames.For example,
(face-attribute 'bold :weight) => bold
The functions above did not exist before Emacs 21. For compatibility with older Emacs versions, you can use the following functions to set and examine the face attributes which existed in those versions.
These functions set the foreground (or background, respectively) color of face face to color. The argument color should be a string, the name of a color.
Certain shades of gray are implemented by stipple patterns on black-and-white screens.
This function sets the background stipple pattern of face face to pattern. The argument pattern should be the name of a stipple pattern defined by the X server, or
nilmeaning don't use stipple.Normally there is no need to pay attention to stipple patterns, because they are used automatically to handle certain shades of gray.
This function sets the font of face face.
In Emacs 21, this actually sets the attributes
:family,:width,:height,:weight, and:slantaccording to the font name font.In Emacs 20, this sets the font attribute. Once you set the font explicitly, the bold and italic attributes cease to have any effect, because the precise font that you specified is used.
This function specifies whether face should be bold. If bold-p is non-
nil, that means yes;nilmeans no.In Emacs 21, this sets the
:weightattribute. In Emacs 20, it sets the:boldattribute.
This function specifies whether face should be italic. If italic-p is non-
nil, that means yes;nilmeans no.In Emacs 21, this sets the
:slantattribute. In Emacs 20, it sets the:italicattribute.
This function sets the underline attribute of face face. Non-
nilmeans do underline;nilmeans don't.
This function inverts the
:inverse-videoattribute of face face. If the attribute isnil, this function sets it tot, and vice versa.
These functions examine the attributes of a face. If you don't
specify frame, they refer to the default data for new frames.
They return the symbol unspecified if the face doesn't define any
value for that attribute.
These functions return the foreground color (or background color, respectively) of face face, as a string.
This function returns the name of the background stipple pattern of face face, or
nilif it doesn't have one.
This function returns
tif face is bold—that is, if it is bolder than normal. It returnsnilotherwise.
This function returns
tif face is italic or oblique,nilotherwise.
This function returns the
:underlineattribute of face face.
This function returns the
:inverse-videoattribute of face face.
Here are the ways to specify which faces to use for display of text:
default face is used as the ultimate
default for all text. (In Emacs 19 and 20, the default
face is used only when no other face is specified.)
For a mode line or header line, the face modeline or
header-line is used just before default.
face property; if
so, the faces and face attributes specified there apply. See Special Properties.
If the character has a mouse-face property, that is used instead
of the face property when the mouse is “near enough” to the
character.
face and mouse-face
properties too; they apply to all the text covered by the overlay.
region (see Standard Faces).
If these various sources together specify more than one face for a particular character, Emacs merges the attributes of the various faces specified. The attributes of the faces of special glyphs come first; then comes the face for region highlighting, if appropriate; then come attributes of faces from overlays, followed by those from text properties, and last the default face.
When multiple overlays cover one character, an overlay with higher priority overrides those with lower priority. See Overlays.
In Emacs 20, if an attribute such as the font or a color is not
specified in any of the above ways, the frame's own font or color is
used. In newer Emacs versions, this cannot happen, because the
default face specifies all attributes—in fact, the frame's own
font and colors are synonymous with those of the default face.
Selecting a font means mapping the specified face attributes for a character to a font that is available on a particular display. The face attributes, as determined by face merging, specify most of the font choice, but not all. Part of the choice depends on what character it is.
For multibyte characters, typically each font covers only one
character set. So each character set (see Character Sets) specifies
a registry and encoding to use, with the character set's
x-charset-registry property. Its value is a string containing
the registry and the encoding, with a dash between them:
(plist-get (charset-plist 'latin-iso8859-1)
'x-charset-registry)
=> "ISO8859-1"
Unibyte text does not have character sets, so displaying a unibyte
character takes the registry and encoding from the variable
face-default-registry.
This variable specifies which registry and encoding to use in choosing fonts for unibyte characters. The value is initialized at Emacs startup time from the font the user specified for Emacs.
If the face specifies a fontset name, that fontset determines a pattern for fonts of the given charset. If the face specifies a font family, a font pattern is constructed.
Emacs tries to find an available font for the given face attributes and character's registry and encoding. If there is a font that matches exactly, it is used, of course. The hard case is when no available font exactly fits the specification. Then Emacs looks for one that is “close”—one attribute at a time. You can specify the order to consider the attributes. In the case where a specified font family is not available, you can specify a set of mappings for alternatives to try.
This variable specifies the order of importance of the face attributes
:width,:height,:weight, and:slant. The value should be a list containing those four symbols, in order of decreasing importance.Font selection first finds the best available matches for the first attribute listed; then, among the fonts which are best in that way, it searches for the best matches in the second attribute, and so on.
The attributes
:weightand:widthhave symbolic values in a range centered aroundnormal. Matches that are more extreme (farther fromnormal) are somewhat preferred to matches that are less extreme (closer tonormal); this is designed to ensure that non-normal faces contrast with normal ones, whenever possible.The default is
(:width :height :weight :slant), which means first find the fonts closest to the specified:width, then—among the fonts with that width—find a best match for the specified font height, and so on.One example of a case where this variable makes a difference is when the default font has no italic equivalent. With the default ordering, the
italicface will use a non-italic font that is similar to the default one. But if you put:slantbefore:height, theitalicface will use an italic font, even if its height is not quite right.
This variable lets you specify alternative font families to try, if a given family is specified and doesn't exist. Each element should have this form:
(family alternate-families...)If family is specified but not available, Emacs will try the other families given in alternate-families, one by one, until it finds a family that does exist.
This variable lets you specify alternative font registries to try, if a given registry is specified and doesn't exist. Each element should have this form:
(registry alternate-registries...)If registry is specified but not available, Emacs will try the other registries given in alternate-registries, one by one, until it finds a registry that does exist.
Emacs can make use of scalable fonts, but by default it does not use them, since the use of too many or too big scalable fonts can crash XFree86 servers.
This variable controls which scalable fonts to use. A value of
nil, the default, means do not use scalable fonts.tmeans to use any scalable font that seems appropriate for the text.Otherwise, the value must be a list of regular expressions. Then a scalable font is enabled for use if its name matches any regular expression in the list. For example,
(setq scalable-fonts-allowed '("muleindian-2$"))allows the use of scalable fonts with registry
muleindian-2.
This function clears the face cache for all frames. If unload-p is non-
nil, that means to unload all unused fonts as well.
Here are additional functions for creating and working with faces.
This function defines a new face named name, initially with all attributes
nil. It does nothing if there is already a face named name.
This function defines the face new-name as a copy of the existing face named old-face. It creates the face new-name if that doesn't already exist.
If the optional argument frame is given, this function applies only to that frame. Otherwise it applies to each frame individually, copying attributes from old-face in each frame to new-face in the same frame.
If the optional argument new-frame is given, then
copy-facecopies the attributes of old-face in frame to new-name in new-frame.
This function returns the documentation string of face face, or
nilif none was specified for it.
This returns
tif the faces face1 and face2 have the same attributes for display.
This returns
tif the face face displays differently from the default face. A face is considered to be “the same” as the default face if each attribute is either the same as that of the default face, or unspecified (meaning to inherit from the default).
Starting with Emacs 21, a hook is available for automatically assigning faces to text in the buffer. This hook is used for part of the implementation of Font-Lock mode.
This variable holds a list of functions that are called by Emacs redisplay as needed to assign faces automatically to text in the buffer.
The functions are called in the order listed, with one argument, a buffer position pos. Each function should attempt to assign faces to the text in the current buffer starting at pos.
Each function should record the faces they assign by setting the
faceproperty. It should also add a non-nilfontifiedproperty for all the text it has assigned faces to. That property tells redisplay that faces have been assigned to that text already.It is probably a good idea for each function to do nothing if the character after pos already has a non-
nilfontifiedproperty, but this is not required. If one function overrides the assignments made by a previous one, the properties as they are after the last function finishes are the ones that really matter.For efficiency, we recommend writing these functions so that they usually assign faces to around 400 to 600 characters at each call.
This function returns a list of available font names that match pattern. If the optional arguments face and frame are specified, then the list is limited to fonts that are the same size as face currently is on frame.
The argument pattern should be a string, perhaps with wildcard characters: the ‘*’ character matches any substring, and the ‘?’ character matches any single character. Pattern matching of font names ignores case.
If you specify face and frame, face should be a face name (a symbol) and frame should be a frame.
The optional argument maximum sets a limit on how many fonts to return. If this is non-
nil, then the return value is truncated after the first maximum matching fonts. Specifying a small value for maximum can make this function much faster, in cases where many fonts match the pattern.
These additional functions are available starting in Emacs 21.
This function returns a list describing the available fonts for family family on frame. If family is omitted or
nil, this list applies to all families, and therefore, it contains all available fonts. Otherwise, family must be a string; it may contain the wildcards ‘?’ and ‘*’.The list describes the display that frame is on; if frame is omitted or
nil, it applies to the selected frame's display (see Input Focus).The list contains a vector of the following form for each font:
[family width point-size weight slant fixed-p full registry-and-encoding]The first five elements correspond to face attributes; if you specify these attributes for a face, it will use this font.
The last three elements give additional information about the font. fixed-p is non-nil if the font is fixed-pitch. full is the full name of the font, and registry-and-encoding is a string giving the registry and encoding of the font.
The result list is sorted according to the current face font sort order.
This function returns a list of the font families available for frame's display. If frame is omitted or
nil, it describes the selected frame's display (see Input Focus).The value is a list of elements of this form:
(family . fixed-p)Here family is a font family, and fixed-p is non-
nilif fonts of that family are fixed-pitch.
This variable specifies maximum number of fonts to consider in font matching. The function
x-family-fontswill not return more than that many fonts, and font selection will consider only that many fonts when searching a matching font for face attributes. The default is currently 100.
A fontset is a list of fonts, each assigned to a range of character codes. An individual font cannot display the whole range of characters that Emacs supports, but a fontset can. Fontsets have names, just as fonts do, and you can use a fontset name in place of a font name when you specify the “font” for a frame or a face. Here is information about defining a fontset under Lisp program control.
This function defines a new fontset according to the specification string fontset-spec. The string should have this format:
fontpattern, [charsetname:fontname]...Whitespace characters before and after the commas are ignored.
The first part of the string, fontpattern, should have the form of a standard X font name, except that the last two fields should be ‘fontset-alias’.
The new fontset has two names, one long and one short. The long name is fontpattern in its entirety. The short name is ‘fontset-alias’. You can refer to the fontset by either name. If a fontset with the same name already exists, an error is signaled, unless noerror is non-
nil, in which case this function does nothing.If optional argument style-variant-p is non-
nil, that says to create bold, italic and bold-italic variants of the fontset as well. These variant fontsets do not have a short name, only a long one, which is made by altering fontpattern to indicate the bold or italic status.The specification string also says which fonts to use in the fontset. See below for the details.
The construct ‘charset:font’ specifies which font to use (in this fontset) for one particular character set. Here, charset is the name of a character set, and font is the font to use for that character set. You can use this construct any number of times in the specification string.
For the remaining character sets, those that you don't specify explicitly, Emacs chooses a font based on fontpattern: it replaces ‘fontset-alias’ with a value that names one character set. For the ascii character set, ‘fontset-alias’ is replaced with ‘ISO8859-1’.
In addition, when several consecutive fields are wildcards, Emacs collapses them into a single wildcard. This is to prevent use of auto-scaled fonts. Fonts made by scaling larger fonts are not usable for editing, and scaling a smaller font is not useful because it is better to use the smaller font in its own size, which Emacs does.
Thus if fontpattern is this,
-*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
the font specification for ascii characters would be this:
-*-fixed-medium-r-normal-*-24-*-ISO8859-1
and the font specification for Chinese GB2312 characters would be this:
-*-fixed-medium-r-normal-*-24-*-gb2312*-*
You may not have any Chinese font matching the above font specification. Most X distributions include only Chinese fonts that have ‘song ti’ or ‘fangsong ti’ in the family field. In such a case, ‘Fontset-n’ can be specified as below:
Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
Then, the font specifications for all but Chinese GB2312 characters have ‘fixed’ in the family field, and the font specification for Chinese GB2312 characters has a wild card ‘*’ in the family field.
display Property
The display text property (or overlay property) is used to
insert images into text, and also control other aspects of how text
displays. These features are available starting in Emacs 21. The value
of the display property should be a display specification, or a
list or vector containing several display specifications. The rest of
this section describes several kinds of display specifications and what
they mean.
To display a space of specified width and/or height, use a display
specification of the form (space . props), where
props is a property list (a list of alternating properties and
values). You can put this property on one or more consecutive
characters; a space of the specified height and width is displayed in
place of all of those characters. These are the properties you
can use to specify the weight of the space:
:width width:relative-width factordisplay property. The space width is the width of that
character, multiplied by factor.
:align-to hposExactly one of the above properties should be used. You can also specify the height of the space, with other properties:
:height height:relative-height factor:ascent ascentYou should not use both :height and :relative-height
together.
(image . image-props)((margin nil) string)Recursive display specifications are not supported, i.e. string
display specifications that have a display specification property
themselves.
(space-width factor)(height height)(+ n)(- n)height bound to the current specified font height.
(raise factor)factor must be a number, which is interpreted as a multiple of the height of the affected text. If it is positive, that means to display the characters raised. If it is negative, that means to display them lower down.
If the text also has a height display specification, that does
not affect the amount of raising or lowering, which is based on the
faces used for the text.
A buffer can have blank areas called display margins on the left
and on the right. Ordinary text never appears in these areas, but you
can put things into the display margins using the display
property.
To put text in the left or right display margin of the window, use a
display specification of the form (margin right-margin) or
(margin left-margin) on it. To put an image in a display margin,
use that display specification along with the display specification for
the image.
Before the display margins can display anything, you must give them a nonzero width. The usual way to do that is to set these variables:
This variable specifies the width of the left margin. It is buffer-local in all buffers.
This variable specifies the width of the right margin. It is buffer-local in all buffers.
Setting these variables does not immediately affect the window. These
variables are checked when a new buffer is displayed in the window.
Thus, you can make changes take effect by calling
set-window-buffer.
You can also set the margin widths immediately.
This function specifies the margin widths for window window. The argument left controls the left margin and right controls the right margin (default
0).
This function returns the left and right margins of window as a cons cell of the form
(left.right). If window isnil, the selected window is used.
You can make any display specification conditional. To do that,
package it in another list of the form (when condition .
spec). Then the specification spec applies only when
condition evaluates to a non-nil value. During the
evaluation, object is bound to the string or buffer having the
conditional display property. position and
buffer-position are bound to the position within object
and the buffer position where the display property was found,
respectively. Both positions can be different when object is a
string.
To display an image in an Emacs buffer, you must first create an image
descriptor, then use it as a display specifier in the display
property of text that is displayed (see Display Property). Like the
display property, this feature is available starting in Emacs 21.
Emacs can display a number of different image formats; some of them
are supported only if particular support libraries are installed on your
machine. The supported image formats include XBM, XPM (needing the
libraries libXpm version 3.4k and libz), GIF (needing
libungif 4.1.0), Postscript, PBM, JPEG (needing the
libjpeg library version v6a), TIFF (needing libtiff v3.4),
and PNG (needing libpng 1.0.2).
You specify one of these formats with an image type symbol. The image
type symbols are xbm, xpm, gif, postscript,
pbm, jpeg, tiff, and png.
This variable contains a list of those image type symbols that are supported in the current configuration.
An image description is a list of the form (image
. props), where props is a property list containing
alternating keyword symbols (symbols whose names start with a colon) and
their values. You can use any Lisp object as a property, but the only
properties that have any special meaning are certain symbols, all of
them keywords.
Every image descriptor must contain the property :type
type to specify the format of the image. The value of type
should be an image type symbol; for example, xpm for an image in
XPM format.
Here is a list of other properties that are meaningful for all image types:
:file file:file property specifies to load the image from file
file. If file is not an absolute file name, it is expanded
in data-directory.
:data data:data property specifies the actual contents of the image.
Each image must use either :data or :file, but not both.
For most image types, the value of the :data property should be a
string containing the image data; we recommend using a unibyte string.
Before using :data, look for further information in the section
below describing the specific image format. For some image types,
:data may not be supported; for some, it allows other data types;
for some, :data alone is not enough, so you need to use other
image properties along with :data.
:margin margin:margin property specifies how many pixels to add as an
extra margin around the image. The value, margin, must be a a
non-negative number, or a pair (x . y) of such
numbers. If it is a pair, x specifies how many pixels to add
horizontally, and y specifies how many pixels to add vertically.
If :margin is not specified, the default is zero.
:ascent ascent:ascent property specifies the amount of the image's
height to use for its ascent—that is, the part above the baseline.
The value, ascent, must be a number in the range 0 to 100, or
the symbol center.
If ascent is a number, that percentage of the image's height is used for its ascent.
If ascent is center, the image is vertically centered
around a centerline which would be the vertical centerline of text drawn
at the position of the image, in the manner specified by the text
properties and overlays that apply to the image.
If this property is omitted, it defaults to 50.
:relief relief:relief property, if non-nil, adds a shadow rectangle
around the image. The value, relief, specifies the width of the
shadow lines, in pixels. If relief is negative, shadows are drawn
so that the image appears as a pressed button; otherwise, it appears as
an unpressed button.
:conversion algorithm:conversion property, if non-nil, specifies a
conversion algorithm that should be applied to the image before it is
displayed; the value, algorithm, specifies which algorithm.
laplaceemboss(edge-detection :matrix matrix :color-adjust adjust) (x-1/y-1 x/y-1 x+1/y-1
x-1/y x/y x+1/y
x-1/y+1 x/y+1 x+1/y+1)
The resulting pixel is computed from the color intensity of the color resulting from summing up the RGB values of surrounding pixels, multiplied by the specified factors, and dividing that sum by the sum of the factors' absolute values.
Laplace edge-detection currently uses a matrix of
(1 0 0
0 0 0
9 9 -1)
Emboss edge-detection uses a matrix of
( 2 -1 0
-1 0 1
0 1 -2)
disabled:mask maskheuristic or (heuristic bg), build
a clipping mask for the image, so that the background of a frame is
visible behind the image. If bg is not specified, or if bg
is t, determine the background color of the image by looking at
the four corners of the image, assuming the most frequently occurring
color from the corners is the background color of the image. Otherwise,
bg must be a list (red green blue)
specifying the color to assume for the background of the image.
If mask is nil, remove a mask from the image, if it has one. Images
in some formats include a mask which can be removed by specifying
:mask nil.
This function returns
tif image spec has a mask bitmap. frame is the frame on which the image will be displayed. framenilor omitted means to use the selected frame (see Input Focus).
To use XBM format, specify xbm as the image type. This image
format doesn't require an external library, so images of this type are
always supported.
Additional image properties supported for the xbm image type are:
:foreground foregroundnil for the default color. This color is
used for each pixel in the XBM that is 1. The default is the frame's
foreground color.
:background backgroundnil for the default color. This color is
used for each pixel in the XBM that is 0. The default is the frame's
background color.
If you specify an XBM image using data within Emacs instead of an external file, use the following three properties:
:data data:height and :width.
:height and :width in this case,
because omitting them is what indicates the data has the format of an
XBM file. The file contents specify the height and width of the image.
height bits. In this case, you must specify
:height and :width, both to indicate that the string
contains just the bits rather than a whole XBM file, and to specify the
size of the image.
:width width:height height
To use XPM format, specify xpm as the image type. The
additional image property :color-symbols is also meaningful with
the xpm image type:
:color-symbols symbols(name . color). In each element, name is
the name of a color as it appears in the image file, and color
specifies the actual color to use for displaying that name.
For GIF images, specify image type gif. Because of the patents
in the US covering the LZW algorithm, the continued use of GIF format is
a problem for the whole Internet; to end this problem, it is a good idea
for everyone, even outside the US, to stop using GIFS right away
(http://www.burnallgifs.org/). But if you still want to use
them, Emacs can display them.
:index index:index to specify one image from a GIF file that
contains more than one image. This property specifies use of image
number index from the file. An error is signaled if the GIF file
doesn't contain an image with index index.
To use Postscript for an image, specify image type postscript.
This works only if you have Ghostscript installed. You must always use
these three properties:
:pt-width width:pt-height height:bounding-box box %%BoundingBox: 22 171 567 738
Displaying Postscript images from Lisp data is not currently implemented, but it may be implemented by the time you read this. See the etc/NEWS file to make sure.
For PBM images, specify image type pbm. Color, gray-scale and
monochromatic images are supported. For mono PBM images, two additional
image properties are supported.
:foreground foregroundnil for the default color. This color is
used for each pixel in the XBM that is 1. The default is the frame's
foreground color.
:background backgroundnil for the default color. This color is
used for each pixel in the XBM that is 0. The default is the frame's
background color.
For JPEG images, specify image type jpeg.
For TIFF images, specify image type tiff.
For PNG images, specify image type png.
The functions create-image, defimage and
find-image provide convenient ways to create image descriptors.
This function creates and returns an image descriptor which uses the data in file.
The optional argument type is a symbol specifying the image type. If type is omitted or
nil,create-imagetries to determine the image type from the file's first few bytes, or else from the file's name.The remaining arguments, props, specify additional image properties—for example,
(create-image "foo.xpm" 'xpm :heuristic-mask t)The function returns
nilif images of this type are not supported. Otherwise it returns an image descriptor.
This macro defines variable as an image name. The second argument, doc, is an optional documentation string. The remaining arguments, specs, specify alternative ways to display the image.
Each argument in specs has the form of a property list, and each one should specify at least the
:typeproperty and the:fileproperty. Here is an example:(defimage test-image '((:type xpm :file "~/test1.xpm") (:type xbm :file "~/test1.xbm")))
defimagetests each argument, one by one, to see if it is usable—that is, if the type is supported and the file exists. The first usable argument is used to make an image descriptor which is stored in the variable variable.If none of the alternatives will work, then variable is defined as
nil.
This function provides a convenient way to find an image satisfying one of a list of image specifications specs.
Each specification in specs is a property list with contents depending on image type. All specifications must at least contain the properties
:typetype and either:filefile or:dataDATA, where type is a symbol specifying the image type, e.g.xbm, file is the file to load the image from, and data is a string containing the actual image data. The first specification in the list whose type is supported, and file exists, is used to construct the image specification to be returned. If no specification is satisfied,nilis returned.The image is looked for first on
load-pathand then indata-directory.
You can use an image descriptor by setting up the display
property yourself, but it is easier to use the functions in this
section.
This function inserts image in the current buffer at point. The value image should be an image descriptor; it could be a value returned by
create-image, or the value of a symbol defined withdefimage. The argument string specifies the text to put in the buffer to hold the image.The argument area specifies whether to put the image in a margin. If it is
left-margin, the image appears in the left margin;right-marginspecifies the right margin. If area isnilor omitted, the image is displayed at point within the buffer's text.Internally, this function inserts string in the buffer, and gives it a
displayproperty which specifies image. See Display Property.
This function puts image image in front of pos in the current buffer. The argument pos should be an integer or a marker. It specifies the buffer position where the image should appear. The argument string specifies the text that should hold the image as an alternative to the default.
The argument image must be an image descriptor, perhaps returned by
create-imageor stored bydefimage.The argument area specifies whether to put the image in a margin. If it is
left-margin, the image appears in the left margin;right-marginspecifies the right margin. If area isnilor omitted, the image is displayed at point within the buffer's text.Internally, this function creates an overlay, and gives it a
before-stringproperty containing text that has adisplayproperty whose value is the image. (Whew!)
This function removes images in buffer between positions start and end. If buffer is omitted or
nil, images are removed from the current buffer.This removes only images that were put into buffer the way
put-imagedoes it, not images that were inserted withinsert-imageor in other ways.
This function returns the size of an image as a pair
(width.height). spec is an image specification. pixels non-nil means return sizes measured in pixels, otherwise return sizes measured in canonical character units (fractions of the width/height of the frame's default font). frame is the frame on which the image will be displayed. frame null or omitted means use the selected frame (see Input Focus).
Emacs stores images in an image cache when it displays them, so it can display them again more efficiently. It removes an image from the cache when it hasn't been displayed for a specified period of time.
When an image is looked up in the cache, its specification is compared
with cached image specifications using equal. This means that
all images with equal specifications share the same image in the cache.
This variable specifies the number of seconds an image can remain in the cache without being displayed. When an image is not displayed for this length of time, Emacs removes it from the image cache.
If the value is
nil, Emacs does not remove images from the cache except when you explicitly clear it. This mode can be useful for debugging.
This function clears the image cache. If frame is non-
nil, only the cache for that frame is cleared. Otherwise all frames' caches are cleared.
This section describes the mechanism by which Emacs shows a matching open parenthesis when the user inserts a close parenthesis.
The value of this variable should be a function (of no arguments) to be called whenever a character with close parenthesis syntax is inserted. The value of
blink-paren-functionmay benil, in which case nothing is done.
This variable specifies the maximum distance to scan for a matching parenthesis before giving up.
This variable specifies the number of seconds for the cursor to remain at the matching parenthesis. A fraction of a second often gives good results, but the default is 1, which works on all systems.
This function is the default value of
blink-paren-function. It assumes that point follows a character with close parenthesis syntax and moves the cursor momentarily to the matching opening character. If that character is not already on the screen, it displays the character's context in the echo area. To avoid long delays, this function does not search farther thanblink-matching-paren-distancecharacters.Here is an example of calling this function explicitly.
(defun interactive-blink-matching-open () "Indicate momentarily the start of sexp before point." (interactive) (let ((blink-matching-paren-distance (buffer-size)) (blink-matching-paren t)) (blink-matching-open)))
This variable controls whether Emacs uses inverse video for all text on the screen. Non-
nilmeans yes,nilmeans no. The default isnil.
This variable controls the use of inverse video for mode lines and menu bars. If it is non-
nil, then these lines are displayed in inverse video. Otherwise, these lines are displayed normally, just like other text. The default ist.For window frames, this feature actually applies the face named
mode-line; that face is normally set up as the inverse of the default face, unless you change it.
The usual display conventions define how to display each character code. You can override these conventions by setting up a display table (see Display Tables). Here are the usual display conventions:
tab-width.
ctl-arrow. If it is
non-nil, these codes map to sequences of two glyphs, where the
first glyph is the ascii code for ‘^’. (A display table can
specify a glyph to use instead of ‘^’.) Otherwise, these codes map
just like the codes in the range 128 to 255.
On MS-DOS terminals, Emacs arranges by default for the character code 127 to be mapped to the glyph code 127, which normally displays as an empty polygon. This glyph is used to display non-ascii characters that the MS-DOS terminal doesn't support. See MS-DOS and MULE.
The usual display conventions apply even when there is a display
table, for any character whose entry in the active display table is
nil. Thus, when you set up a display table, you need only
specify the characters for which you want special behavior.
These display rules apply to carriage return (character code 13), when it appears in the buffer. But that character may not appear in the buffer where you expect it, if it was eliminated as part of end-of-line conversion (see Coding System Basics).
These variables affect the way certain characters are displayed on the
screen. Since they change the number of columns the characters occupy,
they also affect the indentation functions. These variables also affect
how the mode line is displayed; if you want to force redisplay of the
mode line using the new values, call the function
force-mode-line-update (see Mode Line Format).
This buffer-local variable controls how control characters are displayed. If it is non-
nil, they are displayed as a caret followed by the character: ‘^A’. If it isnil, they are displayed as a backslash followed by three octal digits: ‘\001’.
The value of this variable is the default value for
ctl-arrowin buffers that do not override it. See Default Value.
When this is non-
nil, Emacs displays a special glyph in each empty line at the end of the buffer, on terminals that support it (window systems).
The value of this variable is the spacing between tab stops used for displaying tab characters in Emacs buffers. The value is in units of columns, and the default is 8. Note that this feature is completely independent of the user-settable tab stops used by the command
tab-to-tab-stop. See Indent Tabs.
You can use the display table feature to control how all possible character codes display on the screen. This is useful for displaying European languages that have letters not in the ascii character set.
The display table maps each character code into a sequence of glyphs, each glyph being a graphic that takes up one character position on the screen. You can also define how to display each glyph on your terminal, using the glyph table.
Display tables affect how the mode line is displayed; if you want to
force redisplay of the mode line using a new display table, call
force-mode-line-update (see Mode Line Format).
A display table is actually a char-table (see Char-Tables) with
display-table as its subtype.
This creates and returns a display table. The table initially has
nilin all elements.
The ordinary elements of the display table are indexed by character
codes; the element at index c says how to display the character
code c. The value should be nil or a vector of glyph
values (see Glyphs). If an element is nil, it says to
display that character according to the usual display conventions
(see Usual Display).
If you use the display table to change the display of newline characters, the whole buffer will be displayed as one long “line.”
The display table also has six “extra slots” which serve special
purposes. Here is a table of their meanings; nil in any slot
means to use the default for that slot, as stated below.
For example, here is how to construct a display table that mimics the
effect of setting ctl-arrow to a non-nil value:
(setq disptab (make-display-table))
(let ((i 0))
(while (< i 32)
(or (= i ?\t) (= i ?\n)
(aset disptab i (vector ?^ (+ i 64))))
(setq i (1+ i)))
(aset disptab 127 (vector ?^ ??)))
This function returns the value of the extra slot slot of display-table. The argument slot may be a number from 0 to 5 inclusive, or a slot name (symbol). Valid symbols are
truncation,wrap,escape,control,selective-display, andvertical-border.
This function stores value in the extra slot slot of display-table. The argument slot may be a number from 0 to 5 inclusive, or a slot name (symbol). Valid symbols are
truncation,wrap,escape,control,selective-display, andvertical-border.
This function displays a description of the display table display-table in a help buffer.
This command displays a description of the current display table in a help buffer.
Each window can specify a display table, and so can each buffer. When a buffer b is displayed in window w, display uses the display table for window w if it has one; otherwise, the display table for buffer b if it has one; otherwise, the standard display table if any. The display table chosen is called the active display table.
This function returns window's display table, or
nilif window does not have an assigned display table.
This function sets the display table of window to table. The argument table should be either a display table or
nil.
This variable is automatically buffer-local in all buffers; its value in a particular buffer specifies the display table for that buffer. If it is
nil, that means the buffer does not have an assigned display table.
This variable's value is the default display table, used whenever a window has no display table and neither does the buffer displayed in that window. This variable is
nilby default.
If there is no display table to use for a particular window—that is,
if the window specifies none, its buffer specifies none, and
standard-display-table is nil—then Emacs uses the usual
display conventions for all character codes in that window. See Usual Display.
A number of functions for changing the standard display table are defined in the library disp-table.
A glyph is a generalization of a character; it stands for an image that takes up a single character position on the screen. Glyphs are represented in Lisp as integers, just as characters are.
The meaning of each integer, as a glyph, is defined by the glyph
table, which is the value of the variable glyph-table.
The value of this variable is the current glyph table. It should be a vector; the gth element defines glyph code g. If the value is
nilinstead of a vector, then all glyphs are simple (see below). The glyph table is not used on windowed displays.
Here are the possible types of elements in the glyph table:
nilIf a glyph code is greater than or equal to the length of the glyph table, that code is automatically simple.
This function returns a newly-allocated glyph code which is set up to display by sending string to the terminal.
This section describes how to make Emacs ring the bell (or blink the screen) to attract the user's attention. Be conservative about how often you do this; frequent bells can become irritating. Also be careful not to use just beeping when signaling an error is more appropriate. (See Errors.)
This function beeps, or flashes the screen (see
visible-bellbelow). It also terminates any keyboard macro currently executing unless do-not-terminate is non-nil.
This variable determines whether Emacs should flash the screen to represent a bell. Non-
nilmeans yes,nilmeans no. This is effective on a window system, and on a character-only terminal provided the terminal's Termcap entry defines the visible bell capability (‘vb’).
If this is non-
nil, it specifies how Emacs should “ring the bell.” Its value should be a function of no arguments. If this is non-nil, it takes precedence over thevisible-bellvariable.
Emacs works with several window systems, most notably the X Window System. Both Emacs and X use the term “window”, but use it differently. An Emacs frame is a single window as far as X is concerned; the individual Emacs windows are not known to X at all.
This variable tells Lisp programs what window system Emacs is running under. The possible values are
This variable is a normal hook which Emacs runs after handling the initialization files. Emacs runs this hook after it has completed loading your init file, the default initialization file (if any), and the terminal-specific Lisp code, and running the hook
term-setup-hook.This hook is used for internal purposes: setting up communication with the window system, and creating the initial window. Users should not interfere with it.
There are many customizations that you can use to make the calendar and diary suit your personal tastes.
If you set the variable view-diary-entries-initially to
t, calling up the calendar automatically displays the diary
entries for the current date as well. The diary dates appear only if
the current date is visible. If you add both of the following lines to
your init file:
(setq view-diary-entries-initially t)
(calendar)
this displays both the calendar and diary windows whenever you start Emacs.
Similarly, if you set the variable
view-calendar-holidays-initially to t, entering the
calendar automatically displays a list of holidays for the current
three-month period. The holiday list appears in a separate
window.
You can set the variable mark-diary-entries-in-calendar to
t in order to mark any dates with diary entries. This takes
effect whenever the calendar window contents are recomputed. There are
two ways of marking these dates: by changing the face (see Faces),
or by placing a plus sign (‘+’) beside the date.
Similarly, setting the variable mark-holidays-in-calendar to
t marks holiday dates, either with a change of face or with an
asterisk (‘*’).
The variable calendar-holiday-marker specifies how to mark a
date as being a holiday. Its value may be a character to insert next to
the date, or a face name to use for displaying the date. Likewise, the
variable diary-entry-marker specifies how to mark a date that has
diary entries. The calendar creates faces named holiday-face and
diary-face for these purposes; those symbols are the default
values of these variables.
The variable calendar-load-hook is a normal hook run when the
calendar package is first loaded (before actually starting to display
the calendar).
Starting the calendar runs the normal hook
initial-calendar-window-hook. Recomputation of the calendar
display does not run this hook. But if you leave the calendar with the
q command and reenter it, the hook runs again.
The variable today-visible-calendar-hook is a normal hook run
after the calendar buffer has been prepared with the calendar when the
current date is visible in the window. One use of this hook is to
replace today's date with asterisks; to do that, use the hook function
calendar-star-date.
(add-hook 'today-visible-calendar-hook 'calendar-star-date)
Another standard hook function marks the current date, either by changing its face or by adding an asterisk. Here's how to use it:
(add-hook 'today-visible-calendar-hook 'calendar-mark-today)
The variable calendar-today-marker specifies how to mark today's
date. Its value should be a character to insert next to the date or a
face name to use for displaying the date. A face named
calendar-today-face is provided for this purpose; that symbol is
the default for this variable.
A similar normal hook, today-invisible-calendar-hook is run if
the current date is not visible in the window.
Starting in Emacs 21, each of the calendar cursor motion commands
runs the hook calendar-move-hook after it moves the cursor.
Emacs knows about holidays defined by entries on one of several lists.
You can customize these lists of holidays to your own needs, adding or
deleting holidays. The lists of holidays that Emacs uses are for
general holidays (general-holidays), local holidays
(local-holidays), Christian holidays (christian-holidays),
Hebrew (Jewish) holidays (hebrew-holidays), Islamic (Moslem)
holidays (islamic-holidays), and other holidays
(other-holidays).
The general holidays are, by default, holidays common throughout the
United States. To eliminate these holidays, set general-holidays
to nil.
There are no default local holidays (but sites may supply some). You
can set the variable local-holidays to any list of holidays, as
described below.
By default, Emacs does not include all the holidays of the religions
that it knows, only those commonly found in secular calendars. For a
more extensive collection of religious holidays, you can set any (or
all) of the variables all-christian-calendar-holidays,
all-hebrew-calendar-holidays, or
all-islamic-calendar-holidays to t. If you want to
eliminate the religious holidays, set any or all of the corresponding
variables christian-holidays, hebrew-holidays, and
islamic-holidays to nil.
You can set the variable other-holidays to any list of
holidays. This list, normally empty, is intended for individual use.
Each of the lists (general-holidays, local-holidays,
christian-holidays, hebrew-holidays,
islamic-holidays, and other-holidays) is a list of
holiday forms, each holiday form describing a holiday (or
sometimes a list of holidays).
Here is a table of the possible kinds of holiday form. Day numbers and month numbers count starting from 1, but “dayname” numbers count Sunday as 0. The element string is always the name of the holiday, as a string.
(holiday-fixed month day string)(holiday-float month dayname k string)(holiday-hebrew month day string)(holiday-islamic month day string)(holiday-julian month day string)(holiday-sexp sexp string)year to compute and return the date of a
holiday, or nil if the holiday doesn't happen this year. The
value of sexp must represent the date as a list of the form
(month day year).
(if condition holiday-form)(function [args])For example, suppose you want to add Bastille Day, celebrated in France on July 14. You can do this as follows:
(setq other-holidays '((holiday-fixed 7 14 "Bastille Day")))
The holiday form (holiday-fixed 7 14 "Bastille Day") specifies the
fourteenth day of the seventh month (July).
Many holidays occur on a specific day of the week, at a specific time of month. Here is a holiday form describing Hurricane Supplication Day, celebrated in the Virgin Islands on the fourth Monday in August:
(holiday-float 8 1 4 "Hurricane Supplication Day")
Here the 8 specifies August, the 1 specifies Monday (Sunday is 0, Tuesday is 2, and so on), and the 4 specifies the fourth occurrence in the month (1 specifies the first occurrence, 2 the second occurrence, −1 the last occurrence, −2 the second-to-last occurrence, and so on).
You can specify holidays that occur on fixed days of the Hebrew, Islamic, and Julian calendars too. For example,
(setq other-holidays
'((holiday-hebrew 10 2 "Last day of Hanukkah")
(holiday-islamic 3 12 "Mohammed's Birthday")
(holiday-julian 4 2 "Jefferson's Birthday")))
adds the last day of Hanukkah (since the Hebrew months are numbered with 1 starting from Nisan), the Islamic feast celebrating Mohammed's birthday (since the Islamic months are numbered from 1 starting with Muharram), and Thomas Jefferson's birthday, which is 2 April 1743 on the Julian calendar.
To include a holiday conditionally, use either Emacs Lisp's if or the
holiday-sexp form. For example, American presidential elections
occur on the first Tuesday after the first Monday in November of years
divisible by 4:
(holiday-sexp (if (= 0 (% year 4))
(calendar-gregorian-from-absolute
(1+ (calendar-dayname-on-or-before
1 (+ 6 (calendar-absolute-from-gregorian
(list 11 1 year))))))
"US Presidential Election"))
or
(if (= 0 (% displayed-year 4))
(fixed 11
(extract-calendar-day
(calendar-gregorian-from-absolute
(1+ (calendar-dayname-on-or-before
1 (+ 6 (calendar-absolute-from-gregorian
(list 11 1 displayed-year)))))))
"US Presidential Election"))
Some holidays just don't fit into any of these forms because special
calculations are involved in their determination. In such cases you
must write a Lisp function to do the calculation. To include eclipses,
for example, add (eclipses) to other-holidays
and write an Emacs Lisp function eclipses that returns a
(possibly empty) list of the relevant Gregorian dates among the range
visible in the calendar window, with descriptive strings, like this:
(((6 27 1991) "Lunar Eclipse") ((7 11 1991) "Solar Eclipse") ... )
You can customize the manner of displaying dates in the diary, in mode
lines, and in messages by setting calendar-date-display-form.
This variable holds a list of expressions that can involve the variables
month, day, and year, which are all numbers in
string form, and monthname and dayname, which are both
alphabetic strings. In the American style, the default value of this
list is as follows:
((if dayname (concat dayname ", ")) monthname " " day ", " year)
while in the European style this value is the default:
((if dayname (concat dayname ", ")) day " " monthname " " year)
The ISO standard date representation is this:
(year "-" month "-" day)
This specifies a typical American format:
(month "/" day "/" (substring year -2))
The calendar and diary by default display times of day in the
conventional American style with the hours from 1 through 12, minutes,
and either ‘am’ or ‘pm’. If you prefer the European style,
also known in the US as military, in which the hours go from 00 to 23,
you can alter the variable calendar-time-display-form. This
variable is a list of expressions that can involve the variables
12-hours, 24-hours, and minutes, which are all
numbers in string form, and am-pm and time-zone, which are
both alphabetic strings. The default value of
calendar-time-display-form is as follows:
(12-hours ":" minutes am-pm
(if time-zone " (") time-zone (if time-zone ")"))
Here is a value that provides European style times:
(24-hours ":" minutes
(if time-zone " (") time-zone (if time-zone ")"))
Emacs understands the difference between standard time and daylight savings time—the times given for sunrise, sunset, solstices, equinoxes, and the phases of the moon take that into account. The rules for daylight savings time vary from place to place and have also varied historically from year to year. To do the job properly, Emacs needs to know which rules to use.
Some operating systems keep track of the rules that apply to the place where you are; on these systems, Emacs gets the information it needs from the system automatically. If some or all of this information is missing, Emacs fills in the gaps with the rules currently used in Cambridge, Massachusetts, which is the center of GNU's world.
If the default choice of rules is not appropriate for your location,
you can tell Emacs the rules to use by setting the variables
calendar-daylight-savings-starts and
calendar-daylight-savings-ends. Their values should be Lisp
expressions that refer to the variable year, and evaluate to the
Gregorian date on which daylight savings time starts or (respectively)
ends, in the form of a list (month day year).
The values should be nil if your area does not use daylight
savings time.
Emacs uses these expressions to determine the start and end dates of daylight savings time as holidays and for correcting times of day in the solar and lunar calculations.
The values for Cambridge, Massachusetts are as follows:
(calendar-nth-named-day 1 0 4 year)
(calendar-nth-named-day -1 0 10 year)
i.e., the first 0th day (Sunday) of the fourth month (April) in
the year specified by year, and the last Sunday of the tenth month
(October) of that year. If daylight savings time were
changed to start on October 1, you would set
calendar-daylight-savings-starts to this:
(list 10 1 year)
For a more complex example, suppose daylight savings time begins on
the first of Nisan on the Hebrew calendar. You should set
calendar-daylight-savings-starts to this value:
(calendar-gregorian-from-absolute
(calendar-absolute-from-hebrew
(list 1 1 (+ year 3760))))
because Nisan is the first month in the Hebrew calendar and the Hebrew year differs from the Gregorian year by 3760 at Nisan.
If there is no daylight savings time at your location, or if you want
all times in standard time, set calendar-daylight-savings-starts
and calendar-daylight-savings-ends to nil.
The variable calendar-daylight-time-offset specifies the
difference between daylight savings time and standard time, measured in
minutes. The value for Cambridge is 60.
The variable calendar-daylight-savings-starts-time and the
variable calendar-daylight-savings-ends-time specify the number
of minutes after midnight local time when the transition to and from
daylight savings time should occur. For Cambridge, both variables'
values are 120.
Ordinarily, the mode line of the diary buffer window indicates any
holidays that fall on the date of the diary entries. The process of
checking for holidays can take several seconds, so including holiday
information delays the display of the diary buffer noticeably. If you'd
prefer to have a faster display of the diary buffer but without the
holiday information, set the variable holidays-in-diary-buffer to
nil.
The variable number-of-diary-entries controls the number of
days of diary entries to be displayed at one time. It affects the
initial display when view-diary-entries-initially is t, as
well as the command M-x diary. For example, the default value is
1, which says to display only the current day's diary entries. If the
value is 2, both the current day's and the next day's entries are
displayed. The value can also be a vector of seven elements: for
example, if the value is [0 2 2 2 2 4 1] then no diary entries
appear on Sunday, the current date's and the next day's diary entries
appear Monday through Thursday, Friday through Monday's entries appear
on Friday, while on Saturday only that day's entries appear.
The variable print-diary-entries-hook is a normal hook run
after preparation of a temporary buffer containing just the diary
entries currently visible in the diary buffer. (The other, irrelevant
diary entries are really absent from the temporary buffer; in the diary
buffer, they are merely hidden.) The default value of this hook does
the printing with the command lpr-buffer. If you want to use a
different command to do the printing, just change the value of this
hook. Other uses might include, for example, rearranging the lines into
order by day and time.
You can customize the form of dates in your diary file, if neither the
standard American nor European styles suits your needs, by setting the
variable diary-date-forms. This variable is a list of patterns
for recognizing a date. Each date pattern is a list whose elements may
be regular expressions (see Regular Expressions) or the symbols
month, day, year, monthname, and
dayname. All these elements serve as patterns that match certain
kinds of text in the diary file. In order for the date pattern, as a
whole, to match, all of its elements must match consecutively.
A regular expression in a date pattern matches in its usual fashion, using the standard syntax table altered so that ‘*’ is a word constituent.
The symbols month, day, year, monthname,
and dayname match the month number, day number, year number,
month name, and day name of the date being considered. The symbols that
match numbers allow leading zeros; those that match names allow
three-letter abbreviations and capitalization. All the symbols can
match ‘*’; since ‘*’ in a diary entry means “any day”, “any
month”, and so on, it should match regardless of the date being
considered.
The default value of diary-date-forms in the American style is
this:
((month "/" day "[^/0-9]")
(month "/" day "/" year "[^0-9]")
(monthname " *" day "[^,0-9]")
(monthname " *" day ", *" year "[^0-9]")
(dayname "\\W"))
The date patterns in the list must be mutually exclusive and
must not match any portion of the diary entry itself, just the date and
one character of whitespace. If, to be mutually exclusive, the pattern
must match a portion of the diary entry text—beyond the whitespace
that ends the date—then the first element of the date pattern
must be backup. This causes the date recognizer to back
up to the beginning of the current word of the diary entry, after
finishing the match. Even if you use backup, the date pattern
must absolutely not match more than a portion of the first word of the
diary entry. The default value of diary-date-forms in the
European style is this list:
((day "/" month "[^/0-9]")
(day "/" month "/" year "[^0-9]")
(backup day " *" monthname "\\W+\\<[^*0-9]")
(day " *" monthname " *" year "[^0-9]")
(dayname "\\W"))
Notice the use of backup in the third pattern, because it needs
to match part of a word beyond the date itself to distinguish it from
the fourth pattern.
Your diary file can have entries based on Hebrew or Islamic dates, as well as entries based on the world-standard Gregorian calendar. However, because recognition of such entries is time-consuming and most people don't use them, you must explicitly enable their use. If you want the diary to recognize Hebrew-date diary entries, for example, you must do this:
(add-hook 'nongregorian-diary-listing-hook 'list-hebrew-diary-entries)
(add-hook 'nongregorian-diary-marking-hook 'mark-hebrew-diary-entries)
If you want Islamic-date entries, do this:
(add-hook 'nongregorian-diary-listing-hook 'list-islamic-diary-entries)
(add-hook 'nongregorian-diary-marking-hook 'mark-islamic-diary-entries)
Hebrew- and Islamic-date diary entries have the same formats as Gregorian-date diary entries, except that ‘H’ precedes a Hebrew date and ‘I’ precedes an Islamic date. Moreover, because the Hebrew and Islamic month names are not uniquely specified by the first three letters, you may not abbreviate them. For example, a diary entry for the Hebrew date Heshvan 25 could look like this:
HHeshvan 25 Happy Hebrew birthday!
and would appear in the diary for any date that corresponds to Heshvan 25 on the Hebrew calendar. And here is an Islamic-date diary entry that matches Dhu al-Qada 25:
IDhu al-Qada 25 Happy Islamic birthday!
As with Gregorian-date diary entries, Hebrew- and Islamic-date entries are nonmarking if they are preceded with an ampersand (‘&’).
Here is a table of commands used in the calendar to create diary entries that match the selected date and other dates that are similar in the Hebrew or Islamic calendar:
insert-hebrew-diary-entry).
insert-monthly-hebrew-diary-entry). This diary
entry matches any date that has the same Hebrew day-within-month as the
selected date.
insert-yearly-hebrew-diary-entry). This diary
entry matches any date which has the same Hebrew month and day-within-month
as the selected date.
insert-islamic-diary-entry).
insert-monthly-islamic-diary-entry).
insert-yearly-islamic-diary-entry).
These commands work much like the corresponding commands for ordinary diary entries: they apply to the date that point is on in the calendar window, and what they do is insert just the date portion of a diary entry at the end of your diary file. You must then insert the rest of the diary entry.
Diary display works by preparing the diary buffer and then running the
hook diary-display-hook. The default value of this hook
(simple-diary-display) hides the irrelevant diary entries and
then displays the buffer. However, if you specify the hook as follows,
(add-hook 'diary-display-hook 'fancy-diary-display)
this enables fancy diary display. It displays diary entries and holidays by copying them into a special buffer that exists only for the sake of display. Copying to a separate buffer provides an opportunity to change the displayed text to make it prettier—for example, to sort the entries by the dates they apply to.
As with simple diary display, you can print a hard copy of the buffer
with print-diary-entries. To print a hard copy of a day-by-day
diary for a week, position point on Sunday of that week, type
7 d, and then do M-x print-diary-entries. As usual, the
inclusion of the holidays slows down the display slightly; you can speed
things up by setting the variable holidays-in-diary-buffer to
nil.
Ordinarily, the fancy diary buffer does not show days for which there are
no diary entries, even if that day is a holiday. If you want such days to be
shown in the fancy diary buffer, set the variable
diary-list-include-blanks to t.
If you use the fancy diary display, you can use the normal hook
list-diary-entries-hook to sort each day's diary entries by their
time of day. Here's how:
(add-hook 'list-diary-entries-hook 'sort-diary-entries t)
For each day, this sorts diary entries that begin with a recognizable time of day according to their times. Diary entries without times come first within each day.
Fancy diary display also has the ability to process included diary files. This permits a group of people to share a diary file for events that apply to all of them. Lines in the diary file of this form:
#include "filename"
includes the diary entries from the file filename in the fancy diary buffer. The include mechanism is recursive, so that included files can include other files, and so on; you must be careful not to have a cycle of inclusions, of course. Here is how to enable the include facility:
(add-hook 'list-diary-entries-hook 'include-other-diary-files)
(add-hook 'mark-diary-entries-hook 'mark-included-diary-files)
The include mechanism works only with the fancy diary display, because ordinary diary display shows the entries directly from your diary file.
Sexp diary entries allow you to do more than just have complicated conditions under which a diary entry applies. If you use the fancy diary display, sexp entries can generate the text of the entry depending on the date itself. For example, an anniversary diary entry can insert the number of years since the anniversary date into the text of the diary entry. Thus the ‘%d’ in this dairy entry:
%%(diary-anniversary 10 31 1948) Arthur's birthday (%d years old)
gets replaced by the age, so on October 31, 1990 the entry appears in the fancy diary buffer like this:
Arthur's birthday (42 years old)
If the diary file instead contains this entry:
%%(diary-anniversary 10 31 1948) Arthur's %d%s birthday
the entry in the fancy diary buffer for October 31, 1990 appears like this:
Arthur's 42nd birthday
Similarly, cyclic diary entries can interpolate the number of repetitions that have occurred:
%%(diary-cyclic 50 1 1 1990) Renew medication (%d%s time)
looks like this:
Renew medication (5th time)
in the fancy diary display on September 8, 1990.
There is an early reminder diary sexp that includes its entry in the diary not only on the date of occurrence, but also on earlier dates. For example, if you want a reminder a week before your anniversary, you can use
%%(diary-remind '(diary-anniversary 12 22 1968) 7) Ed's anniversary
and the fancy diary will show
Ed's anniversary
both on December 15 and on December 22.
The function diary-date applies to dates described by a month,
day, year combination, each of which can be an integer, a list of
integers, or t. The value t means all values. For
example,
%%(diary-date '(10 11 12) 22 t) Rake leaves
causes the fancy diary to show
Rake leaves
on October 22, November 22, and December 22 of every year.
The function diary-float allows you to describe diary entries
that apply to dates like the third Friday of November, or the last
Tuesday in April. The parameters are the month, dayname,
and an index n. The entry appears on the nth dayname
of month, where dayname=0 means Sunday, 1 means Monday, and
so on. If n is negative it counts backward from the end of
month. The value of month can be a list of months, a single
month, or t to specify all months. You can also use an optional
parameter day to specify the nth dayname of
month on or after/before day; the value of day defaults
to 1 if n is positive and to the last day of month if
n is negative. For example,
%%(diary-float t 1 -1) Pay rent
causes the fancy diary to show
Pay rent
on the last Monday of every month.
The generality of sexp diary entries lets you specify any diary entry
that you can describe algorithmically. A sexp diary entry contains an
expression that computes whether the entry applies to any given date.
If its value is non-nil, the entry applies to that date;
otherwise, it does not. The expression can use the variable date
to find the date being considered; its value is a list (month
day year) that refers to the Gregorian calendar.
Suppose you get paid on the 21st of the month if it is a weekday, and on the Friday before if the 21st is on a weekend. Here is how to write a sexp diary entry that matches those dates:
&%%(let ((dayname (calendar-day-of-week date))
(day (car (cdr date))))
(or (and (= day 21) (memq dayname '(1 2 3 4 5)))
(and (memq day '(19 20)) (= dayname 5)))
) Pay check deposited
The following sexp diary entries take advantage of the ability (in the fancy diary display) to concoct diary entries whose text varies based on the date:
%%(diary-sunrise-sunset)%%(diary-phases-of-moon)%%(diary-day-of-year)%%(diary-iso-date)%%(diary-julian-date)%%(diary-astro-day-number)%%(diary-hebrew-date)%%(diary-islamic-date)%%(diary-french-date)%%(diary-mayan-date)Thus including the diary entry
&%%(diary-hebrew-date)
causes every day's diary display to contain the equivalent date on the Hebrew calendar, if you are using the fancy diary display. (With simple diary display, the line ‘&%%(diary-hebrew-date)’ appears in the diary for any date, but does nothing particularly useful.)
These functions can be used to construct sexp diary entries based on the Hebrew calendar in certain standard ways:
%%(diary-rosh-hodesh)%%(diary-parasha)%%(diary-sabbath-candles)%%(diary-omer)%%(diary-yahrzeit month day year) nameYou can specify exactly how Emacs reminds you of an appointment, and how far in advance it begins doing so, by setting these variables:
appt-message-warning-timeappt-audiblenil, Emacs rings the
terminal bell for appointment reminders. The default is t.
appt-visiblenil, Emacs displays the appointment
message in the echo area. The default is t.
appt-display-mode-linenil, Emacs displays the number of minutes
to the appointment on the mode line. The default is t.
appt-msg-windownil, Emacs displays the appointment
message in another window. The default is t.
appt-disp-window-functionappt-delete-window-functionappt-display-durationThis chapter is about starting and getting out of Emacs, access to values in the operating system environment, and terminal input, output, and flow control.
See Building Emacs, for related information. See also Display, for additional operating system status information pertaining to the terminal and the screen.
This section describes what Emacs does when it is started, and how you can customize these actions.
The order of operations performed (in startup.el) by Emacs when it is started up is as follows:
load-path, by running the file named
subdirs.el in each directory in the list. Normally this file
adds the directory's subdirectories to the list, and these will be
scanned in their turn. The files subdirs.el are normally
generated automatically by Emacs installation.
LANG.
before-init-hook.
inhibit-default-init
is non-nil. (This is not done in ‘-batch’ mode or if
‘-q’ was specified on the command line.) The library's file name
is usually default.el.
after-init-hook.
initial-major-mode, provided
the buffer ‘*scratch*’ is still current and still in Fundamental
mode.
inhibit-startup-echo-area-message.
emacs-startup-hook and then term-setup-hook.
frame-notice-user-settings, which modifies the
parameters of the selected frame according to whatever the init files
specify.
window-setup-hook. See Window Systems.
inhibit-startup-message is nil, and the
buffer is still empty.
This variable inhibits the initial startup messages (the nonwarranty, etc.). If it is non-
nil, then the messages are not printed.This variable exists so you can set it in your personal init file, once you are familiar with the contents of the startup message. Do not set this variable in the init file of a new user, or in a way that affects more than one user, because that would prevent new users from receiving the information they are supposed to see.
This variable controls the display of the startup echo area message. You can suppress the startup echo area message by adding text with this form to your init file:
(setq inhibit-startup-echo-area-message "your-login-name")Emacs explicitly checks for an expression as shown above in your init file; your login name must appear in the expression as a Lisp string constant. Other methods of setting
inhibit-startup-echo-area-messageto the same value do not inhibit the startup message.This way, you can easily inhibit the message for yourself if you wish, but thoughtless copying of your init file will not inhibit the message for someone else.
When you start Emacs, it normally attempts to load your init file, a file in your home directory. Its normal name is .emacs, but you can alternatively call it .emacs.el, which enables you to byte-compile it (see Byte Compilation); then the actual file loaded will be .emacs.elc.
The command-line switches ‘-q’ and ‘-u’ control whether and
where to find the init file; ‘-q’ says not to load an init file,
and ‘-u user’ says to load user's init file instead of
yours. See Entering Emacs. If
neither option is specified, Emacs uses the LOGNAME environment
variable, or the USER (most systems) or USERNAME (MS
systems) variable, to find your home directory and thus your init file;
this way, even if you have su'd, Emacs still loads your own init file.
If those environment variables are absent, though, Emacs uses your
user-id to find your home directory.
A site may have a default init file, which is the library named
default.el. Emacs finds the default.el file through the
standard search path for libraries (see How Programs Do Loading).
The Emacs distribution does not come with this file; sites may provide
one for local customizations. If the default init file exists, it is
loaded whenever you start Emacs, except in batch mode or if ‘-q’ is
specified. But your own personal init file, if any, is loaded first; if
it sets inhibit-default-init to a non-nil value, then
Emacs does not subsequently load the default.el file.
Another file for site-customization is site-start.el. Emacs loads this before the user's init file. You can inhibit the loading of this file with the option ‘-no-site-file’.
This variable specifies the site-customization file to load before the user's init file. Its normal value is
"site-start". The only way you can change it with real effect is to do so before dumping Emacs.
See Init File Examples, for examples of how to make various commonly desired customizations in your .emacs file.
This variable prevents Emacs from loading the default initialization library file for your session of Emacs. If its value is non-
nil, then the default library is not loaded. The default value isnil.
This normal hook is run, once, just before loading all the init files (the user's init file, default.el, and/or site-start.el). (The only way to change it with real effect is before dumping Emacs.)
This normal hook is run, once, just after loading all the init files (the user's init file, default.el, and/or site-start.el), before loading the terminal-specific library and processing the command-line arguments.
This normal hook is run, once, just after handling the command line arguments, just before
term-setup-hook.
This variable holds the file name of the user's init file. If the actual init file loaded is a compiled file, such as .emacs.elc, the value refers to the corresponding source file.
Each terminal type can have its own Lisp library that Emacs loads when
run on that type of terminal. The library's name is constructed by
concatenating the value of the variable term-file-prefix and the
terminal type (specified by the environment variable TERM).
Normally, term-file-prefix has the value
"term/"; changing this is not recommended. Emacs finds the file
in the normal manner, by searching the load-path directories, and
trying the ‘.elc’ and ‘.el’ suffixes.
The usual function of a terminal-specific library is to enable special
keys to send sequences that Emacs can recognize. It may also need to
set or add to function-key-map if the Termcap entry does not
specify all the terminal's function keys. See Terminal Input.
When the name of the terminal type contains a hyphen, only the part of
the name before the first hyphen is significant in choosing the library
name. Thus, terminal types ‘aaa-48’ and ‘aaa-30-rv’ both use
the term/aaa library. If necessary, the library can evaluate
(getenv "TERM") to find the full name of the terminal
type.
Your init file can prevent the loading of the
terminal-specific library by setting the variable
term-file-prefix to nil. This feature is useful when
experimenting with your own peculiar customizations.
You can also arrange to override some of the actions of the
terminal-specific library by setting the variable
term-setup-hook. This is a normal hook which Emacs runs using
run-hooks at the end of Emacs initialization, after loading both
your init file and any terminal-specific libraries. You can
use this variable to define initializations for terminals that do not
have their own libraries. See Hooks.
If the
term-file-prefixvariable is non-nil, Emacs loads a terminal-specific initialization file as follows:(load (concat term-file-prefix (getenv "TERM")))You may set the
term-file-prefixvariable tonilin your init file if you do not wish to load the terminal-initialization file. To do this, put the following in your init file:(setq term-file-prefix nil).On MS-DOS, if the environment variable
TERMis not set, Emacs uses ‘internal’ as the terminal type.
This variable is a normal hook that Emacs runs after loading your init file, the default initialization file (if any) and the terminal-specific Lisp file.
You can use
term-setup-hookto override the definitions made by a terminal-specific file.
See window-setup-hook in Window Systems, for a related
feature.
You can use command-line arguments to request various actions when you start Emacs. Since you do not need to start Emacs more than once per day, and will often leave your Emacs session running longer than that, command-line arguments are hardly ever used. As a practical matter, it is best to avoid making the habit of using them, since this habit would encourage you to kill and restart Emacs unnecessarily often. These options exist for two reasons: to be compatible with other editors (for invocation by other programs) and to enable shell scripts to run specific Lisp programs.
This section describes how Emacs processes command-line arguments, and how you can customize them.
This function parses the command line that Emacs was called with, processes it, loads the user's init file and displays the startup messages.
The value of this variable is
tonce the command line has been processed.If you redump Emacs by calling
dump-emacs, you may wish to set this variable tonilfirst in order to cause the new dumped Emacs to process its new command-line arguments.
The value of this variable is an alist of user-defined command-line options and associated handler functions. This variable exists so you can add elements to it.
A command-line option is an argument on the command line, which has the form:
-optionThe elements of the
command-switch-alistlook like this:(option . handler-function)The car, option, is a string, the name of a command-line option (not including the initial hyphen). The handler-function is called to handle option, and receives the option name as its sole argument.
In some cases, the option is followed in the command line by an argument. In these cases, the handler-function can find all the remaining command-line arguments in the variable
command-line-args-left. (The entire list of command-line arguments is incommand-line-args.)The command-line arguments are parsed by the
command-line-1function in the startup.el file. See also Command Line Switches and Arguments.
The value of this variable is the list of command-line arguments passed to Emacs.
This variable's value is a list of functions for handling an unrecognized command-line argument. Each time the next argument to be processed has no special meaning, the functions in this list are called, in order of appearance, until one of them returns a non-
nilvalue.These functions are called with no arguments. They can access the command-line argument under consideration through the variable
argi, which is bound temporarily at this point. The remaining arguments (not including the current one) are in the variablecommand-line-args-left.When a function recognizes and processes the argument in
argi, it should return a non-nilvalue to say it has dealt with that argument. If it has also dealt with some of the following arguments, it can indicate that by deleting them fromcommand-line-args-left.If all of these functions return
nil, then the argument is used as a file name to visit.
There are two ways to get out of Emacs: you can kill the Emacs job, which exits permanently, or you can suspend it, which permits you to reenter the Emacs process later. As a practical matter, you seldom kill Emacs—only when you are about to log out. Suspending is much more common.
Killing Emacs means ending the execution of the Emacs process. The
parent process normally resumes control. The low-level primitive for
killing Emacs is kill-emacs.
This function exits the Emacs process and kills it.
If exit-data is an integer, then it is used as the exit status of the Emacs process. (This is useful primarily in batch operation; see Batch Mode.)
If exit-data is a string, its contents are stuffed into the terminal input buffer so that the shell (or whatever program next reads input) can read them.
All the information in the Emacs process, aside from files that have
been saved, is lost when the Emacs process is killed. Because killing
Emacs inadvertently can lose a lot of work, Emacs queries for
confirmation before actually terminating if you have buffers that need
saving or subprocesses that are running. This is done in the function
save-buffers-kill-emacs.
After asking the standard questions,
save-buffers-kill-emacscalls the functions in the listkill-emacs-query-functions, in order of appearance, with no arguments. These functions can ask for additional confirmation from the user. If any of them returnsnil, Emacs is not killed.
This variable is a normal hook; once
save-buffers-kill-emacsis finished with all file saving and confirmation, it runs the functions in this hook.
Suspending Emacs means stopping Emacs temporarily and returning
control to its superior process, which is usually the shell. This
allows you to resume editing later in the same Emacs process, with the
same buffers, the same kill ring, the same undo history, and so on. To
resume Emacs, use the appropriate command in the parent shell—most
likely fg.
Some operating systems do not support suspension of jobs; on these systems, “suspension” actually creates a new shell temporarily as a subprocess of Emacs. Then you would exit the shell to return to Emacs.
Suspension is not useful with window systems, because the Emacs job may not have a parent that can resume it again, and in any case you can give input to some other job such as a shell merely by moving to a different window. Therefore, suspending is not allowed when Emacs is using a window system (X or MS Windows).
This function stops Emacs and returns control to the superior process. If and when the superior process resumes Emacs,
suspend-emacsreturnsnilto its caller in Lisp.If string is non-
nil, its characters are sent to be read as terminal input by Emacs's superior shell. The characters in string are not echoed by the superior shell; only the results appear.Before suspending,
suspend-emacsruns the normal hooksuspend-hook.After the user resumes Emacs,
suspend-emacsruns the normal hooksuspend-resume-hook. See Hooks.The next redisplay after resumption will redraw the entire screen, unless the variable
no-redraw-on-reenteris non-nil(see Refresh Screen).In the following example, note that ‘pwd’ is not echoed after Emacs is suspended. But it is read and executed by the shell.
(suspend-emacs) => nil (add-hook 'suspend-hook (function (lambda () (or (y-or-n-p "Really suspend? ") (error "Suspend cancelled"))))) => (lambda nil (or (y-or-n-p "Really suspend? ") (error "Suspend cancelled"))) (add-hook 'suspend-resume-hook (function (lambda () (message "Resumed!")))) => (lambda nil (message "Resumed!")) (suspend-emacs "pwd") => nil ---------- Buffer: Minibuffer ---------- Really suspend? y ---------- Buffer: Minibuffer ---------- ---------- Parent Shell ---------- lewis@slug[23] % /user/lewis/manual lewis@slug[24] % fg ---------- Echo Area ---------- Resumed!
This variable is a normal hook that Emacs runs on resuming after a suspension.
Emacs provides access to variables in the operating system environment through various functions. These variables include the name of the system, the user's uid, and so on.
This variable holds the GNU configuration name for the hardware/software configuration of your system, as a string. The convenient way to test parts of this string is with
string-match.
The value of this variable is a symbol indicating the type of operating system Emacs is operating on. Here is a table of the possible values:
alpha-vms- VMS on the Alpha.
aix-v3- AIX.
berkeley-unix- Berkeley BSD.
dgux- Data General DGUX operating system.
gnu- the GNU system (using the GNU kernel, which consists of the HURD and Mach).
gnu/linux- A GNU/Linux system—that is, a variant GNU system, using the Linux kernel. (These systems are the ones people often call “Linux,” but actually Linux is just the kernel, not the whole system.)
hpux- Hewlett-Packard HPUX operating system.
irix- Silicon Graphics Irix system.
ms-dos- Microsoft MS-DOS “operating system.” Emacs compiled with DJGPP for MS-DOS binds
system-typetoms-doseven when you run it on MS-Windows.next-mach- NeXT Mach-based system.
rtu- Masscomp RTU, UCB universe.
unisoft-unix- UniSoft UniPlus.
usg-unix-v- AT&T System V.
vax-vms- VAX VMS.
windows-nt- Microsoft windows NT. The same executable supports Windows 9X, but the value of
system-typeiswindows-ntin either case.xenix- SCO Xenix 386.
We do not wish to add new symbols to make finer distinctions unless it is absolutely necessary! In fact, we hope to eliminate some of these alternatives in the future. We recommend using
system-configurationto distinguish between different operating systems.
This function returns the name of the machine you are running on.
(system-name) => "www.gnu.org"
The symbol system-name is a variable as well as a function. In
fact, the function returns whatever value the variable
system-name currently holds. Thus, you can set the variable
system-name in case Emacs is confused about the name of your
system. The variable is also useful for constructing frame titles
(see Frame Titles).
If this variable is non-
nil, it is used instead ofsystem-namefor purposes of generating email addresses. For example, it is used when constructing the default value ofuser-mail-address. See User Identification. (Since this is done when Emacs starts up, the value actually used is the one saved when Emacs was dumped. See Building Emacs.)
This function returns the value of the environment variable var, as a string. Within Emacs, the environment variable values are kept in the Lisp variable
process-environment.(getenv "USER") => "lewis" lewis@slug[10] % printenv PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin USER=lewis TERM=ibmapa16 SHELL=/bin/csh HOME=/user/lewis
This command sets the value of the environment variable named variable to value. Both arguments should be strings. This function works by modifying
process-environment; binding that variable withletis also reasonable practice.
This variable is a list of strings, each describing one environment variable. The functions
getenvandsetenvwork by means of this variable.process-environment => ("l=/usr/stanford/lib/gnuemacs/lisp" "PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin" "USER=lewis" "TERM=ibmapa16" "SHELL=/bin/csh" "HOME=/user/lewis")
This variable holds a string which says which character separates directories in a search path (as found in an environment variable). Its value is
":"for Unix and GNU systems, and";"for MS-DOS and MS-Windows.
This function takes a search path string such as would be the value of the
PATHenvironment variable, and splits it at the separators, returning a list of directory names.nilin this list stands for “use the current directory.” Although the function's name says “colon,” it actually uses the value ofpath-separator.(parse-colon-path ":/foo:/bar") => (nil "/foo/" "/bar/")
This variable holds the program name under which Emacs was invoked. The value is a string, and does not include a directory name.
This variable holds the directory from which the Emacs executable was invoked, or perhaps
nilif that directory cannot be determined.
If non-
nil, this is a directory within which to look for the lib-src and etc subdirectories. This is non-nilwhen Emacs can't find those directories in their standard installed locations, but can find them in a directory related somehow to the one containing the Emacs executable.
This function returns the current 1-minute, 5-minute, and 15-minute load averages, in a list.
By default, the values are integers that are 100 times the system load averages, which indicate the average number of processes trying to run. If use-float is non-
nil, then they are returned as floating point numbers and without multiplying by 100.(load-average) => (169 48 36) (load-average t) => (1.69 0.48 0.36) lewis@rocky[5] % uptime 11:55am up 1 day, 19:37, 3 users, load average: 1.69, 0.48, 0.36
This variable holds the erase character that was selected in the system's terminal driver, before Emacs was started.
This function sets or resets a VMS privilege. (It does not exist on other systems.) The first argument is the privilege name, as a string. The second argument, setp, is
tornil, indicating whether the privilege is to be turned on or off. Its default isnil. The function returnstif successful,nilotherwise.If the third argument, getprv, is non-
nil,setprvdoes not change the privilege, but returnstornilindicating whether the privilege is currently enabled.
This variable says which user's init files should be used by Emacs—or
nilif none. The value reflects command-line options such as ‘-q’ or ‘-u user’.Lisp packages that load files of customizations, or any other sort of user profile, should obey this variable in deciding where to find it. They should load the profile of the user name found in this variable. If
init-file-userisnil, meaning that the ‘-q’ option was used, then Lisp packages should not load any customization files or user profile.
This holds the nominal email address of the user who is using Emacs. Emacs normally sets this variable to a default value after reading your init files, but not if you have already set it. So you can set the variable to some other value in your init file if you do not want to use the default value.
If you don't specify uid, this function returns the name under which the user is logged in. If the environment variable
LOGNAMEis set, that value is used. Otherwise, if the environment variableUSERis set, that value is used. Otherwise, the value is based on the effective uid, not the real uid.If you specify uid, the value is the user name that corresponds to uid (which should be an integer).
(user-login-name) => "lewis"
This function returns the user name corresponding to Emacs's real uid. This ignores the effective uid and ignores the environment variables
LOGNAMEandUSER.
This function returns the full name of the logged-in user—or the value of the environment variable
NAME, if that is set.(user-full-name) => "Bil Lewis"If the Emacs job's user-id does not correspond to any known user (and provided
NAMEis not set), the value is"unknown".If uid is non-
nil, then it should be an integer (a user-id) or a string (a login name). Thenuser-full-namereturns the full name corresponding to that user-id or login name. If you specify a user-id or login name that isn't defined, it returnsnil.
The symbols user-login-name, user-real-login-name and
user-full-name are variables as well as functions. The functions
return the same values that the variables hold. These variables allow
you to “fake out” Emacs by telling the functions what to return. The
variables are also useful for constructing frame titles (see Frame Titles).
This section explains how to determine the current time and the time zone.
This function returns the current time and date as a human-readable string. The format of the string is unvarying; the number of characters used for each part is always the same, so you can reliably use
substringto extract pieces of it. It is wise to count the characters from the beginning of the string rather than from the end, as additional information may some day be added at the end.The argument time-value, if given, specifies a time to format instead of the current time. The argument should be a list whose first two elements are integers. Thus, you can use times obtained from
current-time(see below) and fromfile-attributes(see File Attributes).(current-time-string) => "Wed Oct 14 22:21:05 1987"
This function returns the system's time value as a list of three integers:
(high low microsec). The integers high and low combine to give the number of seconds since 0:00 January 1, 1970 (local time), which is high * 2**16 + low.The third element, microsec, gives the microseconds since the start of the current second (or 0 for systems that return time with the resolution of only one second).
The first two elements can be compared with file time values such as you get with the function
file-attributes. See File Attributes.
This function returns a list describing the time zone that the user is in.
The value has the form
(offset name). Here offset is an integer giving the number of seconds ahead of UTC (east of Greenwich). A negative value means west of Greenwich. The second element, name, is a string giving the name of the time zone. Both elements change when daylight savings time begins or ends; if the user has specified a time zone that does not use a seasonal time adjustment, then the value is constant through time.If the operating system doesn't supply all the information necessary to compute the value, both elements of the list are
nil.The argument time-value, if given, specifies a time to analyze instead of the current time. The argument should be a cons cell containing two integers, or a list whose first two elements are integers. Thus, you can use times obtained from
current-time(see above) and fromfile-attributes(see File Attributes).
This function returns the current time as a floating-point number of seconds since the epoch. The argument time-value, if given, specifies a time to convert instead of the current time. The argument should have the same form as for
current-time-string(see above), and it also accepts the output ofcurrent-timeandfile-attributes.Warning: Since the result is floating point, it may not be exact. Do not use this function if precise time stamps are required.
These functions convert time values (lists of two or three integers)
to strings or to calendrical information. There is also a function to
convert calendrical information to a time value. You can get time
values from the functions current-time (see Time of Day) and
file-attributes (see File Attributes).
Many operating systems are limited to time values that contain 32 bits of information; these systems typically handle only the times from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC. However, some operating systems have larger time values, and can represent times far in the past or future.
Time conversion functions always use the Gregorian calendar, even for dates before the Gregorian calendar was introduced. Year numbers count the number of years since the year 1 B.C., and do not skip zero as traditional Gregorian years do; for example, the year number −37 represents the Gregorian year 38 B.C.
This function converts time (or the current time, if time is omitted) to a string according to format-string. The argument format-string may contain ‘%’-sequences which say to substitute parts of the time. Here is a table of what the ‘%’-sequences mean:
- ‘%a’
- This stands for the abbreviated name of the day of week.
- ‘%A’
- This stands for the full name of the day of week.
- ‘%b’
- This stands for the abbreviated name of the month.
- ‘%B’
- This stands for the full name of the month.
- ‘%c’
- This is a synonym for ‘%x %X’.
- ‘%C’
- This has a locale-specific meaning. In the default locale (named C), it is equivalent to ‘%A, %B %e, %Y’.
- ‘%d’
- This stands for the day of month, zero-padded.
- ‘%D’
- This is a synonym for ‘%m/%d/%y’.
- ‘%e’
- This stands for the day of month, blank-padded.
- ‘%h’
- This is a synonym for ‘%b’.
- ‘%H’
- This stands for the hour (00-23).
- ‘%I’
- This stands for the hour (01-12).
- ‘%j’
- This stands for the day of the year (001-366).
- ‘%k’
- This stands for the hour (0-23), blank padded.
- ‘%l’
- This stands for the hour (1-12), blank padded.
- ‘%m’
- This stands for the month (01-12).
- ‘%M’
- This stands for the minute (00-59).
- ‘%n’
- This stands for a newline.
- ‘%p’
- This stands for ‘AM’ or ‘PM’, as appropriate.
- ‘%r’
- This is a synonym for ‘%I:%M:%S %p’.
- ‘%R’
- This is a synonym for ‘%H:%M’.
- ‘%S’
- This stands for the seconds (00-59).
- ‘%t’
- This stands for a tab character.
- ‘%T’
- This is a synonym for ‘%H:%M:%S’.
- ‘%U’
- This stands for the week of the year (01-52), assuming that weeks start on Sunday.
- ‘%w’
- This stands for the numeric day of week (0-6). Sunday is day 0.
- ‘%W’
- This stands for the week of the year (01-52), assuming that weeks start on Monday.
- ‘%x’
- This has a locale-specific meaning. In the default locale (named ‘C’), it is equivalent to ‘%D’.
- ‘%X’
- This has a locale-specific meaning. In the default locale (named ‘C’), it is equivalent to ‘%T’.
- ‘%y’
- This stands for the year without century (00-99).
- ‘%Y’
- This stands for the year with century.
- ‘%Z’
- This stands for the time zone abbreviation.
You can also specify the field width and type of padding for any of these ‘%’-sequences. This works as in
printf: you write the field width as digits in the middle of a ‘%’-sequences. If you start the field width with ‘0’, it means to pad with zeros. If you start the field width with ‘_’, it means to pad with spaces.For example, ‘%S’ specifies the number of seconds since the minute; ‘%03S’ means to pad this with zeros to 3 positions, ‘%_3S’ to pad with spaces to 3 positions. Plain ‘%3S’ pads with zeros, because that is how ‘%S’ normally pads to two positions.
The characters ‘E’ and ‘O’ act as modifiers when used between ‘%’ and one of the letters in the table above. ‘E’ specifies using the current locale's “alternative” version of the date and time. In a Japanese locale, for example,
%Exmight yield a date format based on the Japanese Emperors' reigns. ‘E’ is allowed in ‘%Ec’, ‘%EC’, ‘%Ex’, ‘%EX’, ‘%Ey’, and ‘%EY’.‘O’ means to use the current locale's “alternative” representation of numbers, instead of the ordinary decimal digits. This is allowed with most letters, all the ones that output numbers.
If universal is non-
nil, that means to describe the time as Universal Time;nilmeans describe it using what Emacs believes is the local time zone (seecurrent-time-zone).This function uses the C library function
strftimeto do most of the work. In order to communicate with that function, it first encodes its argument using the coding system specified bylocale-coding-system(see Locales); afterstrftimereturns the resulting string,format-time-stringdecodes the string using that same coding system.
This function converts a time value into calendrical information. The return value is a list of nine elements, as follows:
(seconds minutes hour day month year dow dst zone)Here is what the elements mean:
- seconds
- The number of seconds past the minute, as an integer between 0 and 59.
- minutes
- The number of minutes past the hour, as an integer between 0 and 59.
- hour
- The hour of the day, as an integer between 0 and 23.
- day
- The day of the month, as an integer between 1 and 31.
- month
- The month of the year, as an integer between 1 and 12.
- year
- The year, an integer typically greater than 1900.
- dow
- The day of week, as an integer between 0 and 6, where 0 stands for Sunday.
- dst
tif daylight savings time is effect, otherwisenil.- zone
- An integer indicating the time zone, as the number of seconds east of Greenwich.
Common Lisp Note: Common Lisp has different meanings for dow and zone.
This function is the inverse of
decode-time. It converts seven items of calendrical data into a time value. For the meanings of the arguments, see the table above underdecode-time.Year numbers less than 100 are not treated specially. If you want them to stand for years above 1900, or years above 2000, you must alter them yourself before you call
encode-time.The optional argument zone defaults to the current time zone and its daylight savings time rules. If specified, it can be either a list (as you would get from
current-time-zone), a string as in theTZenvironment variable, or an integer (as you would get fromdecode-time). The specified zone is used without any further alteration for daylight savings time.If you pass more than seven arguments to
encode-time, the first six are used as seconds through year, the last argument is used as zone, and the arguments in between are ignored. This feature makes it possible to use the elements of a list returned bydecode-timeas the arguments toencode-time, like this:(apply 'encode-time (decode-time ...))You can perform simple date arithmetic by using out-of-range values for the seconds, minutes, hour, day, and month arguments; for example, day 0 means the day preceding the given month.
The operating system puts limits on the range of possible time values; if you try to encode a time that is out of range, an error results.
You can set up a timer to call a function at a specified future time or after a certain length of idleness.
Emacs cannot run timers at any arbitrary point in a Lisp program; it
can run them only when Emacs could accept output from a subprocess:
namely, while waiting or inside certain primitive functions such as
sit-for or read-event which can wait. Therefore, a
timer's execution may be delayed if Emacs is busy. However, the time of
execution is very precise if Emacs is idle.
This function arranges to call function with arguments args at time time. The argument function is a function to call later, and args are the arguments to give it when it is called. The time time is specified as a string.
Absolute times may be specified in a wide variety of formats; this function tries to accept all the commonly used date formats. Valid formats include these two,
year-month-day hour:min:sec timezone hour:min:sec timezone month/day/yearwhere in both examples all fields are numbers; the format that
current-time-stringreturns is also allowed, and many others as well.To specify a relative time, use numbers followed by units. For example:
- ‘1 min’
- denotes 1 minute from now.
- ‘1 min 5 sec’
- denotes 65 seconds from now.
- ‘1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year’
- denotes exactly 103 months, 123 days, and 10862 seconds from now.
For relative time values, Emacs considers a month to be exactly thirty days, and a year to be exactly 365.25 days.
If time is a number (integer or floating point), that specifies a relative time measured in seconds.
The argument repeat specifies how often to repeat the call. If repeat is
nil, there are no repetitions; function is called just once, at time. If repeat is a number, it specifies a repetition period measured in seconds.In most cases, repeat has no effect on when first call takes place—time alone specifies that. There is one exception: if time is
t, then the timer runs whenever the time is a multiple of repeat seconds after the epoch. This is useful for functions likedisplay-time.The function
run-at-timereturns a timer value that identifies the particular scheduled future action. You can use this value to callcancel-timer(see below).
Execute body, but give up after seconds seconds. If body finishes before the time is up,
with-timeoutreturns the value of the last form in body. If, however, the execution of body is cut short by the timeout, thenwith-timeoutexecutes all the timeout-forms and returns the value of the last of them.This macro works by setting a timer to run after seconds seconds. If body finishes before that time, it cancels the timer. If the timer actually runs, it terminates execution of body, then executes timeout-forms.
Since timers can run within a Lisp program only when the program calls a primitive that can wait,
with-timeoutcannot stop executing body while it is in the midst of a computation—only when it calls one of those primitives. So usewith-timeoutonly with a body that waits for input, not one that does a long computation.
The function y-or-n-p-with-timeout provides a simple way to use
a timer to avoid waiting too long for an answer. See Yes-or-No Queries.
Set up a timer which runs when Emacs has been idle for secs seconds. The value of secs may be an integer or a floating point number.
If repeat is
nil, the timer runs just once, the first time Emacs remains idle for a long enough time. More often repeat is non-nil, which means to run the timer each time Emacs remains idle for secs seconds.The function
run-with-idle-timerreturns a timer value which you can use in callingcancel-timer(see below).
Emacs becomes “idle” when it starts waiting for user input, and it
remains idle until the user provides some input. If a timer is set for
five seconds of idleness, it runs approximately five seconds after Emacs
first becomes idle. Even if repeat is non-nil, this timer
will not run again as long as Emacs remains idle, because the duration
of idleness will continue to increase and will not go down to five
seconds again.
Emacs can do various things while idle: garbage collect, autosave or handle data from a subprocess. But these interludes during idleness do not interfere with idle timers, because they do not reset the clock of idleness to zero. An idle timer set for 600 seconds will run when ten minutes have elapsed since the last user command was finished, even if subprocess output has been accepted thousands of times within those ten minutes, and even if there have been garbage collections and autosaves.
When the user supplies input, Emacs becomes non-idle while executing the input. Then it becomes idle again, and all the idle timers that are set up to repeat will subsequently run another time, one by one.
Cancel the requested action for timer, which should be a value previously returned by
run-at-timeorrun-with-idle-timer. This cancels the effect of that call torun-at-time; the arrival of the specified time will not cause anything special to happen.
This section describes functions and variables for recording or manipulating terminal input. See Display, for related functions.
This function sets the mode for reading keyboard input. If interrupt is non-null, then Emacs uses input interrupts. If it is
nil, then it uses cbreak mode. The default setting is system-dependent. Some systems always use cbreak mode regardless of what is specified.When Emacs communicates directly with X, it ignores this argument and uses interrupts if that is the way it knows how to communicate.
If flow is non-
nil, then Emacs uses xon/xoff (C-q, C-s) flow control for output to the terminal. This has no effect except in cbreak mode. See Flow Control.The argument meta controls support for input character codes above 127. If meta is
t, Emacs converts characters with the 8th bit set into Meta characters. If meta isnil, Emacs disregards the 8th bit; this is necessary when the terminal uses it as a parity bit. If meta is neithertnornil, Emacs uses all 8 bits of input unchanged. This is good for terminals that use 8-bit character sets.If quit-char is non-
nil, it specifies the character to use for quitting. Normally this character is C-g. See Quitting.
The current-input-mode function returns the input mode settings
Emacs is currently using.
This function returns the current mode for reading keyboard input. It returns a list, corresponding to the arguments of
set-input-mode, of the form(interrupt flow meta quit)in which:
- interrupt
- is non-
nilwhen Emacs is using interrupt-driven input. Ifnil, Emacs is using cbreak mode.- flow
- is non-
nilif Emacs uses xon/xoff (C-q, C-s) flow control for output to the terminal. This value is meaningful only when interrupt isnil.- meta
- is
tif Emacs treats the eighth bit of input characters as the meta bit;nilmeans Emacs clears the eighth bit of every input character; any other value means Emacs uses all eight bits as the basic character code.- quit
- is the character Emacs currently uses for quitting, usually C-g.
This section describes features for translating input events into
other input events before they become part of key sequences. These
features apply to each event in the order they are described here: each
event is first modified according to extra-keyboard-modifiers,
then translated through keyboard-translate-table (if applicable),
and finally decoded with the specified keyboard coding system. If it is
being read as part of a key sequence, it is then added to the sequence
being read; then subsequences containing it are checked first with
function-key-map and then with key-translation-map.
This variable lets Lisp programs “press” the modifier keys on the keyboard. The value is a bit mask:
- 1
- The <SHIFT> key.
- 2
- The <LOCK> key.
- 4
- The <CTL> key.
- 8
- The <META> key.
Each time the user types a keyboard key, it is altered as if the modifier keys specified in the bit mask were held down.
When using a window system, the program can “press” any of the modifier keys in this way. Otherwise, only the <CTL> and <META> keys can be virtually pressed.
This variable is the translate table for keyboard characters. It lets you reshuffle the keys on the keyboard without changing any command bindings. Its value is normally a char-table, or else
nil.If
keyboard-translate-tableis a char-table (see Char-Tables), then each character read from the keyboard is looked up in this char-table. If the value found there is non-nil, then it is used instead of the actual input character.In the example below, we set
keyboard-translate-tableto a char-table. Then we fill it in to swap the characters C-s and C-\ and the characters C-q and C-^. Subsequently, typing C-\ has all the usual effects of typing C-s, and vice versa. (See Flow Control, for more information on this subject.)(defun evade-flow-control () "Replace C-s with C-\ and C-q with C-^." (interactive) (setq keyboard-translate-table (make-char-table 'keyboard-translate-table nil)) ;; Swap C-s and C-\. (aset keyboard-translate-table ?\034 ?\^s) (aset keyboard-translate-table ?\^s ?\034) ;; Swap C-q and C-^. (aset keyboard-translate-table ?\036 ?\^q) (aset keyboard-translate-table ?\^q ?\036))Note that this translation is the first thing that happens to a character after it is read from the terminal. Record-keeping features such as
recent-keysand dribble files record the characters after translation.
This function modifies
keyboard-translate-tableto translate character code from into character code to. It creates the keyboard translate table if necessary.
The remaining translation features translate subsequences of key
sequences being read. They are implemented in read-key-sequence
and have no effect on input read with read-event.
This variable holds a keymap that describes the character sequences sent by function keys on an ordinary character terminal. This keymap has the same structure as other keymaps, but is used differently: it specifies translations to make while reading key sequences, rather than bindings for key sequences.
If
function-key-map“binds” a key sequence k to a vector v, then when k appears as a subsequence anywhere in a key sequence, it is replaced with the events in v.For example, VT100 terminals send <ESC> O P when the keypad <PF1> key is pressed. Therefore, we want Emacs to translate that sequence of events into the single event
pf1. We accomplish this by “binding” <ESC> O P to[pf1]infunction-key-map, when using a VT100.Thus, typing C-c <PF1> sends the character sequence C-c <ESC> O P; later the function
read-key-sequencetranslates this back into C-c <PF1>, which it returns as the vector[?\C-c pf1].Entries in
function-key-mapare ignored if they conflict with bindings made in the minor mode, local, or global keymaps. The intent is that the character sequences that function keys send should not have command bindings in their own right—but if they do, the ordinary bindings take priority.The value of
function-key-mapis usually set up automatically according to the terminal's Terminfo or Termcap entry, but sometimes those need help from terminal-specific Lisp files. Emacs comes with terminal-specific files for many common terminals; their main purpose is to make entries infunction-key-mapbeyond those that can be deduced from Termcap and Terminfo. See Terminal-Specific.
This variable is another keymap used just like
function-key-mapto translate input events into other events. It differs fromfunction-key-mapin two ways:
key-translation-mapgoes to work afterfunction-key-mapis finished; it receives the results of translation byfunction-key-map.key-translation-mapoverrides actual key bindings. For example, if C-x f has a binding inkey-translation-map, that translation takes effect even though C-x f also has a key binding in the global map.The intent of
key-translation-mapis for users to map one character set to another, including ordinary characters normally bound toself-insert-command.
You can use function-key-map or key-translation-map for
more than simple aliases, by using a function, instead of a key
sequence, as the “translation” of a key. Then this function is called
to compute the translation of that key.
The key translation function receives one argument, which is the prompt
that was specified in read-key-sequence—or nil if the
key sequence is being read by the editor command loop. In most cases
you can ignore the prompt value.
If the function reads input itself, it can have the effect of altering the event that follows. For example, here's how to define C-c h to turn the character that follows into a Hyper character:
(defun hyperify (prompt)
(let ((e (read-event)))
(vector (if (numberp e)
(logior (lsh 1 24) e)
(if (memq 'hyper (event-modifiers e))
e
(add-event-modifier "H-" e))))))
(defun add-event-modifier (string e)
(let ((symbol (if (symbolp e) e (car e))))
(setq symbol (intern (concat string
(symbol-name symbol))))
(if (symbolp e)
symbol
(cons symbol (cdr e)))))
(define-key function-key-map "\C-ch" 'hyperify)
Finally, if you have enabled keyboard character set decoding using
set-keyboard-coding-system, decoding is done after the
translations listed above. See Specifying Coding Systems. In future
Emacs versions, character set decoding may be done before the other
translations.
This function returns a vector containing the last 100 input events from the keyboard or mouse. All input events are included, whether or not they were used as parts of key sequences. Thus, you always get the last 100 input events, not counting events generated by keyboard macros. (These are excluded because they are less interesting for debugging; it should be enough to see the events that invoked the macros.)
A call to
clear-this-command-keys(see Command Loop Info) causes this function to return an empty vector immediately afterward.
This function opens a dribble file named filename. When a dribble file is open, each input event from the keyboard or mouse (but not those from keyboard macros) is written in that file. A non-character event is expressed using its printed representation surrounded by ‘<...>’.
You close the dribble file by calling this function with an argument of
nil.This function is normally used to record the input necessary to trigger an Emacs bug, for the sake of a bug report.
(open-dribble-file "~/dribble") => nil
See also the open-termscript function (see Terminal Output).
The terminal output functions send output to the terminal, or keep
track of output sent to the terminal. The variable baud-rate
tells you what Emacs thinks is the output speed of the terminal.
This variable's value is the output speed of the terminal, as far as Emacs knows. Setting this variable does not change the speed of actual data transmission, but the value is used for calculations such as padding. It also affects decisions about whether to scroll part of the screen or repaint—even when using a window system. (We designed it this way despite the fact that a window system has no true “output speed”, to give you a way to tune these decisions.)
The value is measured in baud.
If you are running across a network, and different parts of the
network work at different baud rates, the value returned by Emacs may be
different from the value used by your local terminal. Some network
protocols communicate the local terminal speed to the remote machine, so
that Emacs and other programs can get the proper value, but others do
not. If Emacs has the wrong value, it makes decisions that are less
than optimal. To fix the problem, set baud-rate.
This function sends string to the terminal without alteration. Control characters in string have terminal-dependent effects.
One use of this function is to define function keys on terminals that have downloadable function key definitions. For example, this is how (on certain terminals) to define function key 4 to move forward four characters (by transmitting the characters C-u C-f to the computer):
(send-string-to-terminal "\eF4\^U\^F") => nil
This function is used to open a termscript file that will record all the characters sent by Emacs to the terminal. It returns
nil. Termscript files are useful for investigating problems where Emacs garbles the screen, problems that are due to incorrect Termcap entries or to undesirable settings of terminal options more often than to actual Emacs bugs. Once you are certain which characters were actually output, you can determine reliably whether they correspond to the Termcap specifications in use.See also
open-dribble-filein Terminal Input.(open-termscript "../junk/termscript") => nil
To play sound using Emacs, use the function play-sound. Only
certain systems are supported; if you call play-sound on a system
which cannot really do the job, it gives an error. Emacs version 20 and
earlier did not support sound at all.
The sound must be stored as a file in RIFF-WAVE format (‘.wav’) or Sun Audio format (‘.au’).
This function plays a specified sound. The argument, sound, has the form
(soundproperties...), where the properties consist of alternating keywords (particular symbols recognized specially) and values corresponding to them.Here is a table of the keywords that are currently meaningful in sound, and their meanings:
:filefile- This specifies the file containing the sound to play. If the file name is not absolute, it is expanded against the directory
data-directory.:datadata- This specifies the sound to play without need to refer to a file. The value, data, should be a string containing the same bytes as a sound file. We recommend using a unibyte string.
:volumevolume- This specifies how loud to play the sound. It should be a number in the range of 0 to 1. The default is to use whatever volume has been specified before.
:devicedevice- This specifies the system device on which to play the sound, as a string. The default device is system-dependent.
Before actually playing the sound,
play-soundcalls the functions in the listplay-sound-functions. Each function is called with one argument, sound.
This function is an alternative interface to playing a sound file specifying an optional volume and device.
A list of functions to be called before playing a sound. Each function is called with one argument, a property list that describes the sound.
To define system-specific X11 keysyms, set the variable
system-key-alist.
This variable's value should be an alist with one element for each system-specific keysym. Each element has the form
(code.symbol), where code is the numeric keysym code (not including the “vendor specific” bit, -2**28), and symbol is the name for the function key.For example
(168 . mute-acute)defines a system-specific key (used by HP X servers) whose numeric code is -2**28 + 168.It is not crucial to exclude from the alist the keysyms of other X servers; those do no harm, as long as they don't conflict with the ones used by the X server actually in use.
The variable is always local to the current terminal, and cannot be buffer-local. See Multiple Displays.
This section attempts to answer the question “Why does Emacs use flow-control characters in its command character set?” For a second view on this issue, read the comments on flow control in the emacs/INSTALL file from the distribution; for help with Termcap entries and DEC terminal concentrators, see emacs/etc/TERMS.
At one time, most terminals did not need flow control, and none used
C-s and C-q for flow control. Therefore, the choice of
C-s and C-q as command characters for searching and quoting
was natural and uncontroversial. With so many commands needing key
assignments, of course we assigned meanings to nearly all ascii
control characters.
Later, some terminals were introduced which required these characters for flow control. They were not very good terminals for full-screen editing, so Emacs maintainers ignored them. In later years, flow control with C-s and C-q became widespread among terminals, but by this time it was usually an option. And the majority of Emacs users, who can turn flow control off, did not want to switch to less mnemonic key bindings for the sake of flow control.
So which usage is “right”—Emacs's or that of some terminal and concentrator manufacturers? This question has no simple answer.
One reason why we are reluctant to cater to the problems caused by C-s and C-q is that they are gratuitous. There are other techniques (albeit less common in practice) for flow control that preserve transparency of the character stream. Note also that their use for flow control is not an official standard. Interestingly, on the model 33 teletype with a paper tape punch (around 1970), C-s and C-q were sent by the computer to turn the punch on and off!
As window systems and PC terminal emulators replace character-only
terminals, the flow control problem is gradually disappearing. For the
mean time, Emacs provides a convenient way of enabling flow control if
you want it: call the function enable-flow-control.
This function enables use of C-s and C-q for output flow control, and provides the characters C-\ and C-^ as aliases for them using
keyboard-translate-table(see Translating Input).
You can use the function enable-flow-control-on in your
init file to enable flow control automatically on certain
terminal types.
This function enables flow control, and the aliases C-\ and C-^, if the terminal type is one of termtypes. For example:
(enable-flow-control-on "vt200" "vt300" "vt101" "vt131")
Here is how enable-flow-control does its job:
(set-input-mode nil t).
keyboard-translate-table to translate C-\ and
C-^ into C-s and C-q. Except at its very
lowest level, Emacs never knows that the characters typed were anything
but C-s and C-q, so you can in effect type them as C-\
and C-^ even when they are input for other commands.
See Translating Input.
If the terminal is the source of the flow control characters, then once
you enable kernel flow control handling, you probably can make do with
less padding than normal for that terminal. You can reduce the amount
of padding by customizing the Termcap entry. You can also reduce it by
setting baud-rate to a smaller value so that Emacs uses a smaller
speed when calculating the padding needed. See Terminal Output.
The command-line option ‘-batch’ causes Emacs to run noninteractively. In this mode, Emacs does not read commands from the terminal, it does not alter the terminal modes, and it does not expect to be outputting to an erasable screen. The idea is that you specify Lisp programs to run; when they are finished, Emacs should exit. The way to specify the programs to run is with ‘-l file’, which loads the library named file, and ‘-f function’, which calls function with no arguments.
Any Lisp program output that would normally go to the echo area,
either using message, or using prin1, etc., with t
as the stream, goes instead to Emacs's standard error descriptor when
in batch mode. Similarly, input that would normally come from the
minibuffer is read from the standard input descriptor.
Thus, Emacs behaves much like a noninteractive
application program. (The echo area output that Emacs itself normally
generates, such as command echoing, is suppressed entirely.)
For those users who live backwards in time, here is information about downgrading to Emacs version 20.4. We hope you will enjoy the greater simplicity that results from the absence of many Emacs 21 features. In the following section, we carry this information back to Emacs 20.3, for which the previous printed edition of this manual was made.
push and pop macros are not defined.
Neither are dolist and dotimes.
display text property has no special meaning; you can use it
freely in Lisp programs, with no effects except what you implement for
yourself. With no images, who needs the display text property?
field text property has no special meaning; buffers are no
longer subdivided into fields. (The division of information into
fields is always rather arbitrary.)
:family,
:height, :width, :weight, and :slant,
have been replaced with a font name, a “bold” flag, and an
“italic” flag.
The attributes :overline, :strike-through and :box
have been eliminated too. Underlining now always has the same color as
the text—using any other color would be bad taste.
With fewer font attributes, there are no functions
set-face-attribute and face-attribute. Instead, you
access these attributes using functions such as face-font, and
set them with functions such as set-face-font. (These functions
were available in Emacs 21, but are not as useful there.)
scroll-bar, menu, border,
cursor, and mouse have been eliminated. They are rather
strange, as faces, and therefore shouldn't really exist. You can use
set-border-color, set-cursor-color and
set-mouse-color to specify the colors for the frame border, the
text cursor, and the mouse cursor. To specify menu colors, use X
resources.
delete-and-extract-region has been deleted; instead, use
buffer-substring to extract the text, then use
delete-region to delete it.
window-size-fixed to get special privileges.
intern-soft no longer accepts a symbol as argument.
bitmap-spec-p has been renamed to
pixmap-spec-p to encourage users to practice Emacs' help system
while trying to find it.
format and message ignore and discard text
properties.
propertize does not exist;
you can get the job done using set-text-properties.
color-values, color-defined-p and
defined-colors have been renamed to x-color-values,
x-color-defined-p and x-defined-colors.
before-string or
after-string property must contain only characters that display
as a single column—control characters, including tabs and newlines,
will give strange results.
write-region
has been eliminated; any non-nil value for the seventh
argument now means to ask the user for confirmation.
buffer-size always reports on the
current buffer.
assq-delete-all has itself been deleted.
So there!
:set-after no longer does anything in
defcustom.
small-temporary-file-directory has no special
meaning. There's only one variable for specifying which directory to
use for temporary files, temporary-file-directory, but not all
Emacs features use it anyway. Some use the TMP environment
variable, and some use the TMPDIR environment variable.
save-some-buffers, pred, is not
nil, then the precise value no longer matters. Any
non-nil value means the same as t: offer to save each
non-file buffer that has a non-nil value for
buffer-offer-save.
inhibit-modification-hooks
has no special meaning.
fontification-functions has been eliminated,
but there are other hooks, such as window-scroll-functions,
that you can use to do a similar job.
redisplay-dont-pause
has no special meaning.
calendar-move-hook has been deleted.
move-to-column treats any non-nil
second argument just like t.
Here are the most important of the features that you will learn to do without in Emacs 20.3:
Here are changes in the Lisp language itself:
line-beginning-position and line-end-position
have been eliminated.
directory-files-and-attributes,
file-attributes-lessp, and file-expand-wildcards, have
been eliminated.
decode-coding-region and encode-coding-region
leave text properties untouched, in case that is useful. (It rarely makes
any sense, though.)
position-bytes and byte-to-position have
been eliminated.
with-output-to-temp-buffer are now
modifiable by default, and use Fundamental mode rather than Help mode.
sref interprets its index argument as a
number of bytes, not a number of characters. And the function
char-bytes actually tries to report on the number of bytes that a
character occupies.
process-running-child-p has been eliminated.
interrupt-process and similar functions no longer do
anything special when the second argument is lambda.
define-prefix-command accepts only two arguments.
read-char,
read-event, and read-char-exclusive has been reversed:
they use the current input method if the argument is if nil.
with-temp-message has been eliminated.
clear-this-command-keys has been eliminated.
gap-position and gap-size have been eliminated.
modify-face, an argument of (nil) has no special
meaning.
find-file
and allied functions.
file-attributes returns the file size and the file inode number
only as a simple integer.
Copyright (C) 2000 Free Software Foundation, Inc.
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Free Documentation License''.
If you have no Invariant Sections, write “with no Invariant Sections” instead of saying which ones are invariant. If you have no Front-Cover Texts, write “no Front-Cover Texts” instead of “Front-Cover Texts being list”; likewise for Back-Cover Texts.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
Copyright © 1989, 1991 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software—to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification follow.
Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.
You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.
These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.
Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.
In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.
The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.
If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.
If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.
It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.
This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.
Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and “any later version”, you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.
If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.
one line to give the program's name and an idea of what it does.
Copyright (C) year name of author
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) year name of author
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'. This is free software, and you are welcome
to redistribute it under certain conditions; type `show c'
for details.
The hypothetical commands ‘show w’ and ‘show c’ should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than ‘show w’ and ‘show c’; they could even be mouse-clicks or menu items—whatever suits your program.
You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the program, if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written
by James Hacker.
signature of Ty Coon, 1 April 1989
Ty Coon, President of Vice
This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License.
This chapter describes no additional features of Emacs Lisp. Instead it gives advice on making effective use of the features described in the previous chapters, and describes conventions Emacs Lisp programmers should follow.
You can automatically check some of the conventions described below by running the command M-x checkdoc RET when visiting a Lisp file. It cannot check all of the conventions, and not all the warnings it gives necessarily correspond to problems, but it is worth examining them all.
Here are conventions that you should follow when writing Emacs Lisp code intended for widespread use:
This recommendation applies even to names for traditional Lisp
primitives that are not primitives in Emacs Lisp—even to
copy-list. Believe it or not, there is more than one plausible
way to define copy-list. Play it safe; append your name prefix
to produce a name like foo-copy-list or mylib-copy-list
instead.
If you write a function that you think ought to be added to Emacs under
a certain name, such as twiddle-files, don't call it by that name
in your program. Call it mylib-twiddle-files in your program,
and send mail to ‘bug-gnu-emacs@gnu.org’ suggesting we add
it to Emacs. If and when we do, we can change the name easily enough.
If one prefix is insufficient, your package may use two or three alternative common prefixes, so long as they make sense.
Separate the prefix from the rest of the symbol name with a hyphen, ‘-’. This will be consistent with Emacs itself and with most Emacs Lisp programs.
provide in each separate
library program, at least if there is more than one entry point to the
program.
require to make sure they are loaded.
(eval-when-compile (require 'bar))
(And the library bar should contain (provide 'bar),
to make the require work.) This will cause bar to be
loaded when you byte-compile foo. Otherwise, you risk compiling
foo without the necessary macro loaded, and that would produce
compiled code that won't work right. See Compiling Macros.
Using eval-when-compile avoids loading bar when
the compiled version of foo is used.
cl package of Common Lisp extensions at
run time. Use of this package is optional, and it is not part of the
standard Emacs namespace. If your package loads cl at run time,
that could cause name clashes for users who don't use that package.
However, there is no problem with using the cl package at compile
time, for the sake of macros. You do that like this:
(eval-when-compile (require 'cl))
framep and frame-live-p.
Instead, define sequences consisting of C-c followed by a control character, a digit, or certain punctuation characters. These sequences are reserved for major modes.
Changing all the Emacs major modes to follow this convention was a lot of work. Abandoning this convention would make that work go to waste, and inconvenience users.
The reason for this rule is that a non-prefix binding for <ESC> in any context prevents recognition of escape sequences as function keys in that context.
For a state which accepts ordinary Emacs commands, or more generally any kind of state in which <ESC> followed by a function key or arrow key is potentially meaningful, then you must not define <ESC> <ESC>, since that would preclude recognizing an escape sequence after <ESC>. In these states, you should define <ESC> <ESC> <ESC> as the way to escape. Otherwise, define <ESC> <ESC> instead.
-mode which turns the feature on or
off, and make it autoload (see Autoload). Design the package so
that simply loading it has no visible effect—that should not enable
the feature.11 Users will request the feature by
invoking the command.
(defalias 'gnus-point-at-bol
(if (fboundp 'point-at-bol)
'point-at-bol
'line-beginning-position))
next-line or previous-line in programs; nearly
always, forward-line is more convenient as well as more
predictable and robust. See Text Lines.
In particular, don't use any of these functions:
beginning-of-buffer, end-of-buffer
replace-string, replace-regexp
If you just want to move point, or replace a certain string, without any of the other features intended for interactive users, you can replace these functions with one or two lines of simple Lisp code.
Vectors are advantageous for tables that are substantial in size and are accessed in random order (not searched front to back), provided there is no need to insert or delete elements (only lists allow that).
message function, not princ. See The Echo Area.
error
(or signal). The function error does not return.
See Signaling Errors.
Do not use message, throw, sleep-for,
or beep to report errors.
interactive, if you use a Lisp expression to produce a list
of arguments, don't try to provide the “correct” default values for
region or position arguments. Instead, provide nil for those
arguments if they were not specified, and have the function body
compute the default value when the argument is nil. For
instance, write this:
(defun foo (pos)
(interactive
(list (if specified specified-pos)))
(unless pos (setq pos default-pos))
...)
rather than this:
(defun foo (pos)
(interactive
(list (if specified specified-pos
default-pos)))
...)
This is so that repetition of the command will recompute these defaults based on the current circumstances.
You do not need to take such precautions when you use interactive specs ‘d’, ‘m’ and ‘r’, because they make special arrangements to recompute the argument values on repetition of the command.
edit-options command does: switch to another buffer and let the
user switch back at will. See Recursive Editing.
defvar definitions for these variables.
Sometimes adding a require for another package is useful to avoid
compilation warnings for variables and functions defined in that
package. If you do this, often it is better if the require acts
only at compile time. Here's how to do that:
(eval-when-compile
(require 'foo)
(defvar bar-baz))
If you bind a variable in one function, and use it or set it in another function, the compiler warns about the latter function unless the variable has a definition. But often these variables have short names, and it is not clean for Lisp packages to define such variable names. Therefore, you should rename the variable to start with the name prefix used for the other functions and variables in your package.
indent-sexp) using the
default indentation parameters.
;; Copyright (C) year name
;; This program is free software; you can redistribute it and/or
;; modify it under the terms of the GNU General Public License as
;; published by the Free Software Foundation; either version 2 of
;; the License, or (at your option) any later version.
;; This program is distributed in the hope that it will be
;; useful, but WITHOUT ANY WARRANTY; without even the implied
;; warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
;; PURPOSE. See the GNU General Public License for more details.
;; You should have received a copy of the GNU General Public
;; License along with this program; if not, write to the Free
;; Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
;; MA 02111-1307 USA
If you have signed papers to assign the copyright to the Foundation, then use ‘Free Software Foundation, Inc.’ as name. Otherwise, use your name.
Here are ways of improving the execution speed of byte-compiled Lisp programs.
memq, member,
assq, or assoc is even faster than explicit iteration. It
can be worth rearranging a data structure so that one of these primitive
search functions can be used.
byte-compile
property. If the property is non-nil, then the function is
handled specially.
For example, the following input will show you that aref is
compiled specially (see Array Functions):
(get 'aref 'byte-compile)
=> byte-compile-two-args
Here are some tips and conventions for the writing of documentation strings. You can check many of these conventions by running the command M-x checkdoc-minor-mode.
The documentation string is not limited to one line; use as many lines as you need to explain the details of how to use the function or variable. Please use complete sentences in the additional lines.
dired-find-file is:
In Dired, visit the file or directory named on this line.
apropos.
You can fill the text if that looks good. However, rather than blindly filling the entire documentation string, you can often make it much more readable by choosing certain line breaks with care. Use blank lines between topics if the documentation string is long.
nil values are equivalent and indicate explicitly what
nil and non-nil mean.
eval refers to its second argument as ‘FORM’, because the
actual argument name is form:
Evaluate FORM and return its value.
Also write metasyntactic variables in capital letters, such as when you show the decomposition of a list or vector into subunits, some of which may vary. ‘KEY’ and ‘VALUE’ in the following example illustrate this practice:
The argument TABLE should be an alist whose elements
have the form (KEY . VALUE). Here, KEY is ...
The argument FOO can be either a number
\(a buffer position) or a string (a file name).
This prevents the open-parenthesis from being treated as the start of a defun (see Defuns).
Help mode automatically creates a hyperlink when a documentation string uses a symbol name inside single quotes, if the symbol has either a function or a variable definition. You do not need to do anything special to make use of this feature. However, when a symbol has both a function definition and a variable definition, and you want to refer to just one of them, you can specify which one by writing one of the words ‘variable’, ‘option’, ‘function’, or ‘command’, immediately before the symbol name. (Case makes no difference in recognizing these indicator words.) For example, if you write
This function sets the variable `buffer-file-name'.
then the hyperlink will refer only to the variable documentation of
buffer-file-name, and not to its function documentation.
If a symbol has a function definition and/or a variable definition, but those are irrelevant to the use of the symbol that you are documenting, you can write the word ‘symbol’ before the symbol name to prevent making any hyperlink. For example,
If the argument KIND-OF-RESULT is the symbol `list',
this function returns a list of all the objects
that satisfy the criterion.
does not make a hyperlink to the documentation, irrelevant here, of the
function list.
To make a hyperlink to Info documentation, write the name of the Info node in single quotes, preceded by ‘info node’ or ‘Info node’. The Info file name defaults to ‘emacs’. For example,
See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'.
forward-char.
(This is normally ‘C-f’, but it may be some other character if the
user has moved key bindings.) See Keys in Documentation.
It is not practical to use ‘\\[...]’ very many times, because display of the documentation string will become slow. So use this to describe the most important commands in your major mode, and then use ‘\\{...}’ to display the rest of the mode's keymap.
We recommend these conventions for where to put comments and how to indent them:
indent-for-comment)
command automatically inserts such a ‘;’ in the right place, or
aligns such a comment if it is already present.
This and following examples are taken from the Emacs sources.
(setq base-version-list ; there was a base
(assoc (substring fn 0 start-vn) ; version to which
file-version-assoc-list)) ; this looks like
; a subversion
(prog1 (setq auto-fill-function
...
...
;; update mode line
(force-mode-line-update)))
We also normally use two semicolons for comments outside functions.
;; This Lisp code is run in Emacs
;; when it is to operate as a server
;; for other processes.
Every function that has no documentation string (presumably one that is
used only internally within the package it belongs to), should instead
have a two-semicolon comment right before the function, explaining what
the function does and how to call it properly. Explain precisely what
each argument means and how the function interprets its possible values.
Another use for triple-semicolon comments is for commenting out lines within a function. We use three semicolons for this precisely so that they remain at the left margin.
(defun foo (a)
;;; This is no longer necessary.
;;; (force-mode-line-update)
(message "Finished with %s" a))
;;;; The kill ring
The indentation commands of the Lisp modes in Emacs, such as M-;
(indent-for-comment) and <TAB> (lisp-indent-line),
automatically indent comments according to these conventions,
depending on the number of semicolons. See Manipulating Comments.
Emacs has conventions for using special comments in Lisp libraries to divide them into sections and give information such as who wrote them. This section explains these conventions.
We'll start with an example, a package that is included in the Emacs distribution.
Parts of this example reflect its status as part of Emacs; for example, the copyright notice lists the Free Software Foundation as the copyright holder, and the copying permission says the file is part of Emacs. When you write a package and post it, the copyright holder would be you (unless your employer claims to own it instead), and you should get the suggested copying permission from the end of the GNU General Public License itself. Don't say your file is part of Emacs if we haven't installed it in Emacs yet!
With that warning out of the way, on to the example:
;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers
;; Copyright (C) 1992 Free Software Foundation, Inc.
;; Author: Eric S. Raymond <esr@snark.thyrsus.com>
;; Maintainer: Eric S. Raymond <esr@snark.thyrsus.com>
;; Created: 14 Jul 1992
;; Version: 1.2
;; Keywords: docs
;; This file is part of GNU Emacs.
...
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.
The very first line should have this format:
;;; filename --- description
The description should be complete in one line.
After the copyright notice come several header comment lines, each beginning with ‘;; header-name:’. Here is a table of the conventional possibilities for header-name:
If there are multiple authors, you can list them on continuation lines
led by ;; and a tab character, like this:
;; Author: Ashwin Ram <Ram-Ashwin@cs.yale.edu>
;; Dave Sill <de5@ornl.gov>
;; Dave Brennan <brennan@hal.com>
;; Eric Raymond <esr@snark.thyrsus.com>
The idea behind the ‘Author’ and ‘Maintainer’ lines is to make possible a Lisp function to “send mail to the maintainer” without having to mine the name out by hand.
Be sure to surround the network address with ‘<...>’ if
you include the person's full name as well as the network address.
finder-by-keyword help command.
Please use that command to see a list of the meaningful keywords.
This field is important; it's how people will find your package when they're looking for things by topic area. To separate the keywords, you can use spaces, commas, or both.
Just about every Lisp library ought to have the ‘Author’ and ‘Keywords’ header comment lines. Use the others if they are appropriate. You can also put in header lines with other header names—they have no standard meanings, so they can't do any harm.
We use additional stylized comments to subdivide the contents of the library file. These should be separated by blank lines from anything else. Here is a table of them:
This chapter describes how the runnable Emacs executable is dumped with the preloaded Lisp libraries in it, how storage is allocated, and some internal aspects of GNU Emacs that may be of interest to C programmers.
This section explains the steps involved in building the Emacs executable. You don't have to know this material to build and install Emacs, since the makefiles do all these things automatically. This information is pertinent to Emacs maintenance.
Compilation of the C source files in the src directory produces an executable file called temacs, also called a bare impure Emacs. It contains the Emacs Lisp interpreter and I/O routines, but not the editing commands.
The command ‘temacs -l loadup’ uses temacs to create the real runnable Emacs executable. These arguments direct temacs to evaluate the Lisp files specified in the file loadup.el. These files set up the normal Emacs editing environment, resulting in an Emacs that is still impure but no longer bare.
It takes a substantial time to load the standard Lisp files. Luckily, you don't have to do this each time you run Emacs; temacs can dump out an executable program called emacs that has these files preloaded. emacs starts more quickly because it does not need to load the files. This is the Emacs executable that is normally installed.
To create emacs, use the command ‘temacs -batch -l loadup dump’. The purpose of ‘-batch’ here is to prevent temacs from trying to initialize any of its data on the terminal; this ensures that the tables of terminal information are empty in the dumped Emacs. The argument ‘dump’ tells loadup.el to dump a new executable named emacs.
Some operating systems don't support dumping. On those systems, you must start Emacs with the ‘temacs -l loadup’ command each time you use it. This takes a substantial time, but since you need to start Emacs once a day at most—or once a week if you never log out—the extra time is not too severe a problem.
You can specify additional files to preload by writing a library named site-load.el that loads them. You may need to add a definition
#define SITELOAD_PURESIZE_EXTRA n
to make n added bytes of pure space to hold the additional files. (Try adding increments of 20000 until it is big enough.) However, the advantage of preloading additional files decreases as machines get faster. On modern machines, it is usually not advisable.
After loadup.el reads site-load.el, it finds the
documentation strings for primitive and preloaded functions (and
variables) in the file etc/DOC where they are stored, by calling
Snarf-documentation (see Accessing Documentation).
You can specify other Lisp expressions to execute just before dumping by putting them in a library named site-init.el. This file is executed after the documentation strings are found.
If you want to preload function or variable definitions, there are three ways you can do this and make their documentation strings accessible when you subsequently run Emacs:
nil value for
byte-compile-dynamic-docstrings as a local variable in each of these
files, and load them with either site-load.el or
site-init.el. (This method has the drawback that the
documentation strings take up space in Emacs all the time.)
It is not advisable to put anything in site-load.el or site-init.el that would alter any of the features that users expect in an ordinary unmodified Emacs. If you feel you must override normal features for your site, do it with default.el, so that users can override your changes if they wish. See Startup Summary.
This function dumps the current state of Emacs into an executable file to-file. It takes symbols from from-file (this is normally the executable file temacs).
If you want to use this function in an Emacs that was already dumped, you must run Emacs with ‘-batch’.
Emacs Lisp uses two kinds of storage for user-created Lisp objects: normal storage and pure storage. Normal storage is where all the new data created during an Emacs session are kept; see the following section for information on normal storage. Pure storage is used for certain data in the preloaded standard Lisp files—data that should never change during actual use of Emacs.
Pure storage is allocated only while temacs is loading the
standard preloaded Lisp libraries. In the file emacs, it is
marked as read-only (on operating systems that permit this), so that
the memory space can be shared by all the Emacs jobs running on the
machine at once. Pure storage is not expandable; a fixed amount is
allocated when Emacs is compiled, and if that is not sufficient for the
preloaded libraries, temacs crashes. If that happens, you must
increase the compilation parameter PURESIZE in the file
src/puresize.h. This normally won't happen unless you try to
preload additional libraries or add features to the standard ones.
This function makes a copy in pure storage of object, and returns it. It copies a string by simply making a new string with the same characters in pure storage. It recursively copies the contents of vectors and cons cells. It does not make copies of other objects such as symbols, but just returns them unchanged. It signals an error if asked to copy markers.
This function is a no-op except while Emacs is being built and dumped; it is usually called only in the file emacs/lisp/loaddefs.el, but a few packages call it just in case you decide to preload them.
The value of this variable is the number of bytes of pure storage allocated so far. Typically, in a dumped Emacs, this number is very close to the total amount of pure storage available—if it were not, we would preallocate less.
This variable determines whether
defunshould make a copy of the function definition in pure storage. If it is non-nil, then the function definition is copied into pure storage.This flag is
twhile loading all of the basic functions for building Emacs initially (allowing those functions to be sharable and non-collectible). Dumping Emacs as an executable always writesnilin this variable, regardless of the value it actually has before and after dumping.You should not change this flag in a running Emacs.
When a program creates a list or the user defines a new function (such as by loading a library), that data is placed in normal storage. If normal storage runs low, then Emacs asks the operating system to allocate more memory in blocks of 1k bytes. Each block is used for one type of Lisp object, so symbols, cons cells, markers, etc., are segregated in distinct blocks in memory. (Vectors, long strings, buffers and certain other editing types, which are fairly large, are allocated in individual blocks, one per object, while small strings are packed into blocks of 8k bytes.)
It is quite common to use some storage for a while, then release it by (for example) killing a buffer or deleting the last pointer to an object. Emacs provides a garbage collector to reclaim this abandoned storage. (This name is traditional, but “garbage recycler” might be a more intuitive metaphor for this facility.)
The garbage collector operates by finding and marking all Lisp objects that are still accessible to Lisp programs. To begin with, it assumes all the symbols, their values and associated function definitions, and any data presently on the stack, are accessible. Any objects that can be reached indirectly through other accessible objects are also accessible.
When marking is finished, all objects still unmarked are garbage. No matter what the Lisp program or the user does, it is impossible to refer to them, since there is no longer a way to reach them. Their space might as well be reused, since no one will miss them. The second (“sweep”) phase of the garbage collector arranges to reuse them.
The sweep phase puts unused cons cells onto a free list
for future allocation; likewise for symbols and markers. It compacts
the accessible strings so they occupy fewer 8k blocks; then it frees the
other 8k blocks. Vectors, buffers, windows, and other large objects are
individually allocated and freed using malloc and free.
Common Lisp note: Unlike other Lisps, GNU Emacs Lisp does not call the garbage collector when the free list is empty. Instead, it simply requests the operating system to allocate more storage, and processing continues untilgc-cons-thresholdbytes have been used.This means that you can make sure that the garbage collector will not run during a certain portion of a Lisp program by calling the garbage collector explicitly just before it (provided that portion of the program does not use so much space as to force a second garbage collection).
This command runs a garbage collection, and returns information on the amount of space in use. (Garbage collection can also occur spontaneously if you use more than
gc-cons-thresholdbytes of Lisp data since the previous garbage collection.)
garbage-collectreturns a list containing the following information:((used-conses . free-conses) (used-syms . free-syms) (used-miscs . free-miscs) used-string-chars used-vector-slots (used-floats . free-floats) (used-intervals . free-intervals) (used-strings . free-strings))Here is an example:
(garbage-collect) => ((106886 . 13184) (9769 . 0) (7731 . 4651) 347543 121628 (31 . 94) (1273 . 168) (25474 . 3569))Here is a table explaining each element:
- used-conses
- The number of cons cells in use.
- free-conses
- The number of cons cells for which space has been obtained from the operating system, but that are not currently being used.
- used-syms
- The number of symbols in use.
- free-syms
- The number of symbols for which space has been obtained from the operating system, but that are not currently being used.
- used-miscs
- The number of miscellaneous objects in use. These include markers and overlays, plus certain objects not visible to users.
- free-miscs
- The number of miscellaneous objects for which space has been obtained from the operating system, but that are not currently being used.
- used-string-chars
- The total size of all strings, in characters.
- used-vector-slots
- The total number of elements of existing vectors.
- used-floats
- The number of floats in use.
- free-floats
- The number of floats for which space has been obtained from the operating system, but that are not currently being used.
- used-intervals
- The number of intervals in use. Intervals are an internal data structure used for representing text properties.
- free-intervals
- The number of intervals for which space has been obtained from the operating system, but that are not currently being used.
- used-strings
- The number of strings in use.
- free-strings
- The number of string headers for which the space was obtained from the operating system, but which are currently not in use. (A string object consists of a header and the storage for the string text itself; the latter is only allocated when the string is created.)
If this variable is non-
nil, Emacs displays a message at the beginning and end of garbage collection. The default value isnil, meaning there are no such messages.
The value of this variable is the number of bytes of storage that must be allocated for Lisp objects after one garbage collection in order to trigger another garbage collection. A cons cell counts as eight bytes, a string as one byte per character plus a few bytes of overhead, and so on; space allocated to the contents of buffers does not count. Note that the subsequent garbage collection does not happen immediately when the threshold is exhausted, but only the next time the Lisp evaluator is called.
The initial threshold value is 400,000. If you specify a larger value, garbage collection will happen less often. This reduces the amount of time spent garbage collecting, but increases total memory use. You may want to do this when running a program that creates lots of Lisp data.
You can make collections more frequent by specifying a smaller value, down to 10,000. A value less than 10,000 will remain in effect only until the subsequent garbage collection, at which time
garbage-collectwill set the threshold back to 10,000.
The value return by garbage-collect describes the amount of
memory used by Lisp data, broken down by data type. By contrast, the
function memory-limit provides information on the total amount of
memory Emacs is currently using.
This function returns the address of the last byte Emacs has allocated, divided by 1024. We divide the value by 1024 to make sure it fits in a Lisp integer.
You can use this to get a general idea of how your actions affect the memory usage.
These functions and variables give information about the total amount
of memory allocation that Emacs has done, broken down by data type.
Note the difference between these and the values returned by
(garbage-collect); those count objects that currently exist, but
these count the number or size of all allocations, including those for
objects that have since been freed.
The total number of cons cells that have been allocated so far in this Emacs session.
The total number of floats that have been allocated so far in this Emacs session.
The total number of vector cells that have been allocated so far in this Emacs session.
The total number of symbols that have been allocated so far in this Emacs session.
The total number of string characters that have been allocated so far in this Emacs session.
The total number of miscellaneous objects that have been allocated so far in this Emacs session. These include markers and overlays, plus certain objects not visible to users.
The total number of intervals that have been allocated so far in this Emacs session.
The total number of strings that have been allocated so far in this Emacs session.
Lisp primitives are Lisp functions implemented in C. The details of interfacing the C function so that Lisp can call it are handled by a few C macros. The only way to really understand how to write new C code is to read the source, but we can explain some things here.
An example of a special form is the definition of or, from
eval.c. (An ordinary function would have the same general
appearance.)
DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
"Eval args until one of them yields non-nil; return that value.\n\
The remaining args are not evalled at all.\n\
If all args return nil, return nil.")
(args)
Lisp_Object args;
{
register Lisp_Object val;
Lisp_Object args_left;
struct gcpro gcpro1;
if (NILP (args))
return Qnil;
args_left = args;
GCPRO1 (args_left);
do
{
val = Feval (Fcar (args_left));
if (!NILP (val))
break;
args_left = Fcdr (args_left);
}
while (!NILP (args_left));
UNGCPRO;
return val;
}
Let's start with a precise explanation of the arguments to the
DEFUN macro. Here is a template for them:
DEFUN (lname, fname, sname, min, max, interactive, doc)
or.
For. Remember that the arguments must
be of type Lisp_Object; various macros and functions for creating
values of type Lisp_Object are declared in the file
lisp.h.
or allows a minimum of zero arguments.
UNEVALLED,
indicating a special form that receives unevaluated arguments, or
MANY, indicating an unlimited number of evaluated arguments (the
equivalent of &rest). Both UNEVALLED and MANY are
macros. If max is a number, it may not be less than min and
it may not be greater than seven.
interactive in a Lisp function. In the case of
or, it is 0 (a null pointer), indicating that or cannot be
called interactively. A value of "" indicates a function that
should receive no arguments when called interactively.
After the call to the DEFUN macro, you must write the argument
name list that every C function must have, followed by ordinary C
declarations for the arguments. For a function with a fixed maximum
number of arguments, declare a C argument for each Lisp argument, and
give them all type Lisp_Object. When a Lisp function has no
upper limit on the number of arguments, its implementation in C actually
receives exactly two arguments: the first is the number of Lisp
arguments, and the second is the address of a block containing their
values. They have types int and Lisp_Object *.
Within the function For itself, note the use of the macros
GCPRO1 and UNGCPRO. GCPRO1 is used to “protect”
a variable from garbage collection—to inform the garbage collector that
it must look in that variable and regard its contents as an accessible
object. This is necessary whenever you call Feval or anything
that can directly or indirectly call Feval. At such a time, any
Lisp object that you intend to refer to again must be protected somehow.
UNGCPRO cancels the protection of the variables that are
protected in the current function. It is necessary to do this explicitly.
For most data types, it suffices to protect at least one pointer to the object; as long as the object is not recycled, all pointers to it remain valid. This is not so for strings, because the garbage collector can move them. When the garbage collector moves a string, it relocates all the pointers it knows about; any other pointers become invalid. Therefore, you must protect all pointers to strings across any point where garbage collection may be possible.
The macro GCPRO1 protects just one local variable. If you want
to protect two, use GCPRO2 instead; repeating GCPRO1 will
not work. Macros GCPRO3 and GCPRO4 also exist.
These macros implicitly use local variables such as gcpro1; you
must declare these explicitly, with type struct gcpro. Thus, if
you use GCPRO2, you must declare gcpro1 and gcpro2.
Alas, we can't explain all the tricky details here.
You must not use C initializers for static or global variables unless the variables are never written once Emacs is dumped. These variables with initializers are allocated in an area of memory that becomes read-only (on certain operating systems) as a result of dumping Emacs. See Pure Storage.
Do not use static variables within functions—place all static
variables at top level in the file. This is necessary because Emacs on
some operating systems defines the keyword static as a null
macro. (This definition is used because those systems put all variables
declared static in a place that becomes read-only after dumping, whether
they have initializers or not.)
Defining the C function is not enough to make a Lisp primitive available; you must also create the Lisp symbol for the primitive and store a suitable subr object in its function cell. The code looks like this:
defsubr (&subr-structure-name);
Here subr-structure-name is the name you used as the third
argument to DEFUN.
If you add a new primitive to a file that already has Lisp primitives
defined in it, find the function (near the end of the file) named
syms_of_something, and add the call to defsubr
there. If the file doesn't have this function, or if you create a new
file, add to it a syms_of_filename (e.g.,
syms_of_myfile). Then find the spot in emacs.c where all
of these functions are called, and add a call to
syms_of_filename there.
The function syms_of_filename is also the place to define
any C variables that are to be visible as Lisp variables.
DEFVAR_LISP makes a C variable of type Lisp_Object visible
in Lisp. DEFVAR_INT makes a C variable of type int
visible in Lisp with a value that is always an integer.
DEFVAR_BOOL makes a C variable of type int visible in Lisp
with a value that is either t or nil. Note that variables
defined with DEFVAR_BOOL are automatically added to the list
byte-boolean-vars used by the byte compiler.
If you define a file-scope C variable of type Lisp_Object,
you must protect it from garbage-collection by calling staticpro
in syms_of_filename, like this:
staticpro (&variable);
Here is another example function, with more complicated arguments. This comes from the code in window.c, and it demonstrates the use of macros and functions to manipulate Lisp objects.
DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
Scoordinates_in_window_p, 2, 2,
"xSpecify coordinate pair: \nXExpression which evals to window: ",
"Return non-nil if COORDINATES is in WINDOW.\n\
COORDINATES is a cons of the form (X . Y), X and Y being distances\n\
...
If they are on the border between WINDOW and its right sibling,\n\
`vertical-line' is returned.")
(coordinates, window)
register Lisp_Object coordinates, window;
{
int x, y;
CHECK_LIVE_WINDOW (window, 0);
CHECK_CONS (coordinates, 1);
x = XINT (Fcar (coordinates));
y = XINT (Fcdr (coordinates));
switch (coordinates_in_window (XWINDOW (window), &x, &y))
{
case 0: /* NOT in window at all. */
return Qnil;
case 1: /* In text part of window. */
return Fcons (make_number (x), make_number (y));
case 2: /* In mode line of window. */
return Qmode_line;
case 3: /* On right border of window. */
return Qvertical_line;
default:
abort ();
}
}
Note that C code cannot call functions by name unless they are defined
in C. The way to call a function written in Lisp is to use
Ffuncall, which embodies the Lisp function funcall. Since
the Lisp function funcall accepts an unlimited number of
arguments, in C it takes two: the number of Lisp-level arguments, and a
one-dimensional array containing their values. The first Lisp-level
argument is the Lisp function to call, and the rest are the arguments to
pass to it. Since Ffuncall can call the evaluator, you must
protect pointers from garbage collection around the call to
Ffuncall.
The C functions call0, call1, call2, and so on,
provide handy ways to call a Lisp function conveniently with a fixed
number of arguments. They work by calling Ffuncall.
eval.c is a very good file to look through for examples; lisp.h contains the definitions for some important macros and functions.
If you define a function which is side-effect free, update the code in
byte-opt.el which binds side-effect-free-fns and
side-effect-and-error-free-fns to include it. This will help the
optimizer.
GNU Emacs Lisp manipulates many different types of data. The actual data are stored in a heap and the only access that programs have to it is through pointers. Pointers are thirty-two bits wide in most implementations. Depending on the operating system and type of machine for which you compile Emacs, twenty-eight bits are used to address the object, and the remaining four bits are used for a GC mark bit and the tag that identifies the object's type.
Because Lisp objects are represented as tagged pointers, it is always
possible to determine the Lisp data type of any object. The C data type
Lisp_Object can hold any Lisp object of any data type. Ordinary
variables have type Lisp_Object, which means they can hold any
type of Lisp value; you can determine the actual data type only at run
time. The same is true for function arguments; if you want a function
to accept only a certain type of argument, you must check the type
explicitly using a suitable predicate (see Type Predicates).
Buffers contain fields not directly accessible by the Lisp programmer. We describe them here, naming them by the names used in the C code. Many are accessible indirectly in Lisp programs via Lisp primitives.
Two structures are used to represent buffers in C. The
buffer_text structure contains fields describing the text of a
buffer; the buffer structure holds other fields. In the case
of indirect buffers, two or more buffer structures reference
the same buffer_text structure.
Here is a list of the struct buffer_text fields:
beggptzgpt_bytez_bytegap_sizemodiffsave_modiffmodiff, as of the last time a
buffer was visited or saved in a file.
overlay_modiffmodiff.
beg_unchangedend_unchangedunchanged_modifiedmodiff at the time of the last redisplay
that finished. If this value matches modiff,
beg_unchanged and end_unchanged contain no useful
information.
overlay_unchanged_modifiedoverlay_modiff at the time of the last
redisplay that finished. If this value matches overlay_modiff,
beg_unchanged and end_unchanged contain no useful
information.
markerschain are the other
markers referring to this buffer text.
intervalsThe fields of struct buffer are:
nextown_textstruct buffer_text structure. In an ordinary buffer,
it holds the buffer contents. In indirect buffers, this field is not
used.
textbuffer_text structure that is used for this
buffer. In an ordinary buffer, this is the own_text field above.
In an indirect buffer, this is the own_text field of the base
buffer.
ptpt_bytebegvbegv_bytezvzv_bytebase_bufferlocal_var_flagsDEFVAR_PER_BUFFER, and their buffer-local bindings are stored in
fields in the buffer structure itself. (Some of these fields are
described in this table.)
modtimeauto_save_modifiedauto_save_failure_timelast_window_startwindow-start position in the buffer as of
the last time the buffer was displayed in a window.
clip_changedprevent_redisplay_optimizations_pundo_listnamefilenamenil.
directorysave_lengthbuffer_text structure because indirect buffers are never saved.
auto_save_file_namebuffer_text because it's not used in indirect buffers at all.
read_onlynil means this buffer is read-only.
markmarkers. See The Mark.
local_var_alistmajor_modelisp-mode.
mode_name"Lisp".
mode_line_formatnil, no mode line will be displayed.
header_line_formatmode_line_format for the mode
line displayed at the top of windows.
keymapabbrev_tablesyntax_tablecategory_tablecase_fold_searchcase-fold-search in this buffer.
tab_widthtab-width in this buffer.
fill_columnfill-column in this buffer.
left_marginleft-margin in this buffer.
auto_fill_functionauto-fill-function in this buffer.
downcase_tableupcase_tablecase_canon_tablecase_eqv_tabletruncate_linestruncate-lines in this buffer.
ctl_arrowctl-arrow in this buffer.
selective_displayselective-display in this buffer.
selective_display_ellipsisselective-display-ellipsis in this buffer.
minor_modesoverwrite_modeoverwrite_mode in this buffer.
abbrev_modeabbrev-mode in this buffer.
display_tablenil if it doesn't
have one. See Display Tables.
save_modifiedmark_activenil if the buffer's mark is active.
overlays_beforeoverlays_afteroverlay_centerenable_multibyte_charactersenable-multibyte-characters—either t or nil.
buffer_file_coding_systembuffer-file-coding-system in this buffer.
file_formatbuffer-file-format in this buffer.
pt_markerbegv_markerbegv for this buffer
when the buffer is not current.
zv_markerzv for this buffer when
the buffer is not current.
file_truenamenil.
invisibility_specbuffer-invisibility-spec in this buffer.
last_selected_windownil
if that window no longer displays this buffer.
display_countleft_margin_widthleft-margin-width in this buffer.
right_margin_widthright-margin-width in this buffer.
indicate_empty_linesnil means indicate empty lines (lines with no text) with a
small bitmap in the fringe, when using a window system that can do it.
display_timescroll_up_aggressivelyscroll-up-aggressively in this buffer.
scroll_down_aggressivelyscroll-down-aggressively in this buffer.
Windows have the following accessible fields:
framemini_pnil if this window is a minibuffer window.
parentParent windows do not display buffers, and play little role in display except to shape their child windows. Emacs Lisp programs usually have no access to the parent windows; they operate on the windows at the leaves of the tree, which actually display buffers.
The following four fields also describe the window tree structure.
hchildnil.
vchildnil.
nextnil in a window that is
the rightmost or bottommost of a group of siblings.
prevnil in a window that
is the leftmost or topmost of a group of siblings.
lefttopheightwidthbufferstartpointmforce_startnil, it says that the window has been
scrolled explicitly by the Lisp program. This affects what the next
redisplay does if point is off the screen: instead of scrolling the
window to show the text around point, it moves point to a location that
is on the screen.
frozen_window_start_pstart of this window should not be changed, even if point
gets invisible.
start_at_line_begnil means current value of start was the beginning of a line
when it was chosen.
too_small_oknil means don't delete this window for becoming “too small”.
height_fixed_puse_timeget-lru-window uses this field.
sequence_numberlast_modifiedmodiff field of the window's buffer, as of the last time
a redisplay completed in this window.
last_overlay_modifiedoverlay_modiff field of the window's buffer, as of the last
time a redisplay completed in this window.
last_pointlast_had_starnil value means the window's buffer was “modified” when the
window was last updated.
vertical_scroll_barleft_margin_widthnil not to
specify it (in which case the buffer's value of left-margin-width
is used.
right_margin_widthwindow_end_posz minus the buffer position of the last glyph
in the current matrix of the window. The value is only valid if
window_end_valid is not nil.
window_end_byteposwindow_end_pos.
window_end_vposwindow_end_pos.
window_end_validnil value if window_end_pos is truly
valid. This is nil if nontrivial redisplay is preempted since in that
case the display that window_end_pos was computed for did not get
onto the screen.
redisplay_end_triggerredisplay-end-trigger-hook.
cursorlast_cursorcursor as of the last redisplay that finished.
phys_cursorphys_cursor_typephys_cursor_on_pcursor_off_plast_cursor_off_pcursor_off_p as of the time of
the last redisplay.
must_be_updated_phscrollvscrolldedicatednil if this window is dedicated to its buffer.
display_tablenil if none is specified for it.
update_mode_linenil means this window's mode line needs to be updated.
base_line_numbernil.
This is used for displaying the line number of point in the mode line.
base_line_posnil meaning none is known.
region_showingnil.
column_number_displayednil
if column numbers are not being displayed.
current_matrixdesired_matrixnamecommandfilternil.
sentinelnil.
bufferpidchildpnil if this is really a child process.
It is nil for a network connection.
markkill_without_querynil, killing Emacs while this process is still
running does not ask for confirmation about killing the process.
raw_status_lowraw_status_highwait system call.
statusprocess-status should return it.
tickupdate_tickpty_flagnil if communication with the subprocess uses a pty;
nil if it uses a pipe.
infdoutfdsubttynil.)
tty_namenil if it is using pipes.
decode_coding_systemdecoding_bufdecoding_carryoverencode_coding_systemencoding_bufencoding_carryoverinherit_coding_system_flagcoding-system of the process buffer from the
coding system used to decode process output.
Here is the complete list of the error symbols in standard Emacs,
grouped by concept. The list includes each symbol's message (on the
error-message property of the symbol) and a cross reference to a
description of how the error can occur.
Each error symbol has an error-conditions property that is a
list of symbols. Normally this list includes the error symbol itself
and the symbol error. Occasionally it includes additional
symbols, which are intermediate classifications, narrower than
error but broader than a single error symbol. For example, all
the errors in accessing files have the condition file-error. If
we do not say here that a certain error symbol has additional error
conditions, that means it has none.
As a special exception, the error symbol quit does not have the
condition error, because quitting is not considered an error.
See Errors, for an explanation of how errors are generated and handled.
error"error"quit"Quit"args-out-of-range"Args out of range"arith-error"Arithmetic error"/ and % in Numbers.
beginning-of-buffer"Beginning of buffer"buffer-read-only"Buffer is read-only"coding-system-error"Invalid coding system"cyclic-function-indirection"Symbol's chain of function indirections\
contains a loop"end-of-buffer"End of buffer"end-of-file"End of file during parsing"file-error,
because it pertains to the Lisp reader, not to file I/O.
See Input Functions.
file-already-existsfile-error.file-date-errorfile-error. It occurs when
copy-file tries and fails to set the last-modification time of
the output file. See Changing Files.
file-errorfile-error is present.file-lockedfile-error.file-supersessionfile-error.ftp-errorfile-error, which results from problems
in accessing a remote file using ftp.invalid-function"Invalid function"invalid-read-syntax"Invalid read syntax"invalid-regexp"Invalid regexp"mark-inactive"Mark inactive"no-catch"No catch for tag"scan-error"Scan error"search-failed"Search failed"setting-constant"Attempt to set a constant symbol"nil and t,
and any symbols that start with ‘:’,
may not be changed.text-read-only"Text is read-only"undefined-color"Undefined color"void-function"Symbol's function definition is void"void-variable"Symbol's value as variable is void"wrong-number-of-arguments"Wrong number of arguments"wrong-type-argument"Wrong type argument"These kinds of error, which are classified as special cases of
arith-error, can occur on certain systems for invalid use of
mathematical functions.
domain-error"Arithmetic domain error"overflow-error"Arithmetic overflow error"range-error"Arithmetic range error"singularity-error"Arithmetic singularity error"underflow-error"Arithmetic underflow error"The table below lists the general-purpose Emacs variables that automatically become buffer-local in each buffer. Most become buffer-local only when set; a few of them are always local in every buffer. Many Lisp packages define such variables for their internal use, but we don't try to list them all here.
abbrev-modeauto-fill-functionbuffer-auto-save-file-namebuffer-backed-upbuffer-display-countbuffer-display-tablebuffer-file-coding-systembuffer-file-formatbuffer-file-namebuffer-file-numberbuffer-file-truenamebuffer-file-typebuffer-invisibility-specbuffer-offer-savebuffer-read-onlybuffer-saved-sizebuffer-undo-listcache-long-line-scanscase-fold-searchctl-arrowcomment-columndefault-directorydefun-prompt-regexpenable-multibyte-charactersfill-columngoal-columnheader-line-formatindicate-empty-linesleft-marginleft-margin-widthlocal-abbrev-tablelocal-write-file-hooksmajor-modemark-activemark-ringminor-modesmode-line-buffer-identificationmode-line-formatmode-line-modifiedmode-line-processmode-nameoverwrite-modeparagraph-separateparagraph-startpoint-before-scrollrequire-final-newlineright-margin-widthscroll-down-aggressivelyscroll-up-aggressivelyselective-displayselective-display-ellipsestab-widthtruncate-linesvc-modeThe following symbols are used as the names for various keymaps. Some of these exist when Emacs is first started, others are loaded only when their respective mode is used. This is not an exhaustive list.
Almost all of these maps are used as local maps. Indeed, of the modes that presently exist, only Vip mode and Terminal mode ever change the global keymap.
Buffer-menu-mode-mapc-mode-mapcommand-history-mapctl-x-4-mapctl-x-5-mapctl-x-mapdebugger-mode-mapdired-mode-mapdired-mode buffers.
edit-abbrevs-mapedit-abbrevs.
edit-tab-stops-mapedit-tab-stops.
electric-buffer-menu-mode-mapelectric-history-mapemacs-lisp-mode-mapfacemenu-menufacemenu-background-menufacemenu-face-menufacemenu-foreground-menufacemenu-indentation-menufacemenu-justification-menufacemenu-special-menufunction-key-mapfundamental-mode-mapHelper-help-mapInfo-edit-mapInfo-mode-mapisearch-mode-mapkey-translation-mapfunction-key-map. See Translating Input.
lisp-interaction-mode-maplisp-mode-mapmenu-bar-edit-menumenu-bar-files-menumenu-bar-help-menumenu-bar-mule-menumenu-bar-search-menumenu-bar-tools-menumode-specific-mapdisplay-bindings),
where it describes the main use of the C-c prefix key.
occur-mode-mapquery-replace-mapquery-replace and related
commands; also for y-or-n-p and map-y-or-n-p. The functions
that use this map do not support prefix keys; they look up one event at a
time.
text-mode-mapview-mode-mapThe following is a list of hook variables that let you provide functions to be called from within Emacs on suitable occasions.
Most of these variables have names ending with ‘-hook’. They are
normal hooks, run by means of run-hooks. The value of such
a hook is a list of functions; the functions are called with no
arguments and their values are completely ignored. The recommended way
to put a new function on such a hook is to call add-hook.
See Hooks, for more information about using hooks.
The variables whose names end in ‘-hooks’ or ‘-functions’ are usually abnormal hooks; their values are lists of functions, but these functions are called in a special way (they are passed arguments, or their values are used). A few of these variables are actually normal hooks which were named before we established the convention that normal hooks' names should end in ‘-hook’.
The variables whose names end in ‘-function’ have single functions as their values. (In older Emacs versions, some of these variables had names ending in ‘-hook’ even though they were not normal hooks; however, we have renamed all of those.)
activate-mark-hookafter-change-functionsafter-init-hookafter-insert-file-functionsafter-make-frame-functionsafter-revert-hookafter-save-hookapropos-mode-hookauto-fill-functionauto-save-hookbefore-change-functionsbefore-init-hookbefore-make-frame-hookbefore-revert-hookblink-paren-functionbuffer-access-fontify-functionsc-mode-hookcalendar-load-hookchange-major-mode-hookcommand-history-hookcommand-line-functionscomment-indent-functiondeactivate-mark-hookdiary-display-hookdiary-hookdired-mode-hookdisabled-command-hookecho-area-clear-hookedit-picture-hookelectric-buffer-menu-mode-hookelectric-command-history-hookelectric-help-mode-hookemacs-lisp-mode-hookfind-file-hooksfind-file-not-found-hooksfirst-change-hookfortran-comment-hookfortran-mode-hookindent-mim-hookinitial-calendar-window-hookkbd-macro-termination-hookkill-buffer-hookkill-buffer-query-functionskill-emacs-hookkill-emacs-query-functionsLaTeX-mode-hookledit-mode-hooklisp-indent-functionlisp-interaction-mode-hooklisp-mode-hooklist-diary-entries-hooklocal-write-file-hooksmail-mode-hookmail-setup-hookmark-diary-entries-hookmedit-mode-hookmenu-bar-update-hookminibuffer-setup-hookminibuffer-exit-hookmouse-position-functionnews-mode-hooknews-reply-mode-hooknews-setup-hooknongregorian-diary-listing-hooknongregorian-diary-marking-hooknroff-mode-hookoutline-mode-hookplain-TeX-mode-hookpost-command-hookpre-abbrev-expand-hookpre-command-hookprint-diary-entries-hookprolog-mode-hookprotect-innocence-hookredisplay-end-trigger-functionsrmail-edit-mode-hookrmail-mode-hookrmail-summary-mode-hookscheme-indent-hookscheme-mode-hookscribe-mode-hookshell-mode-hookshell-set-directory-error-hooksuspend-hooksuspend-resume-hooktemp-buffer-show-functionterm-setup-hookterminal-mode-hookterminal-mode-break-hookTeX-mode-hooktext-mode-hooktoday-visible-calendar-hooktoday-invisible-calendar-hookvi-mode-hookview-hookwindow-configuration-change-hookwindow-scroll-functionswindow-setup-hookwindow-size-change-functionswrite-contents-hookswrite-file-hookswrite-region-annotate-functions%: Arithmetic Operations&define (Edebug): Specification List¬ (Edebug): Specification List&optional: Argument List&optional (Edebug): Specification List&or (Edebug): Specification List&rest: Argument List&rest (Edebug): Specification List*: Arithmetic Operationsinteractive: Using Interactive+: Arithmetic Operations, (with Backquote): Backquote,@ (with Backquote): Backquote-: Arithmetic Operations/: Arithmetic Operations/=: Comparison of Numbers1+: Arithmetic Operations1-: Arithmetic Operations2C-mode-map: Prefix Keys<: Comparison of Numbers<=: Comparison of Numbers=: Comparison of Numbers>: Comparison of Numbers>=: Comparison of Numbersinteractive: Using Interactive`: Backquoteabbrev-all-caps: Abbrev Expansionabbrev-expansion: Abbrev Expansionabbrev-file-name: Abbrev Filesabbrev-mode: Abbrev Modeabbrev-prefix-mark: Abbrev Expansionabbrev-start-location: Abbrev Expansionabbrev-start-location-buffer: Abbrev Expansionabbrev-symbol: Abbrev Expansionabbrev-table-name-list: Abbrev Tablesabbreviate-file-name: Directory Namesabbrevs-changed: Abbrev Filesabort-recursive-edit: Recursive Editingabs: Comparison of Numbersaccept-process-output: Accepting Outputaccess-file: Testing Accessibilityaccessible-keymaps: Scanning Keymapsacos: Math Functionsactivate-mark-hook: The Markactive-minibuffer-window: Minibuffer Miscad-activate: Activation of Advicead-activate-all: Activation of Advicead-activate-regexp: Activation of Advicead-add-advice: Computed Advicead-deactivate: Activation of Advicead-deactivate-all: Activation of Advicead-deactivate-regexp: Activation of Advicead-default-compilation-action: Activation of Advicead-define-subr-args: Subr Argumentsad-disable-advice: Enabling Advicead-disable-regexp: Enabling Advicead-do-it: Around-Advicead-enable-advice: Enabling Advicead-enable-regexp: Enabling Advicead-get-arg: Argument Access in Advicead-get-args: Argument Access in Advicead-return-value: Defining Advicead-set-arg: Argument Access in Advicead-set-args: Argument Access in Advicead-start-advice: Activation of Advicead-stop-advice: Activation of Advicead-unadvise: Defining Advicead-unadvise-all: Defining Advicead-update: Activation of Advicead-update-all: Activation of Advicead-update-regexp: Activation of Adviceadaptive-fill-first-line-regexp: Adaptive Filladaptive-fill-function: Adaptive Filladaptive-fill-mode: Adaptive Filladaptive-fill-regexp: Adaptive Filladd-abbrev: Defining Abbrevsadd-hook: Hooksadd-name-to-file: Changing Filesadd-text-properties: Changing Propertiesadd-to-invisibility-spec: Invisible Textadd-to-list: Setting Variablesafter-change-functions: Change Hooksafter-find-file: Subroutines of Visitingafter-init-hook: Init Fileafter-insert-file-functions: Saving Propertiesafter-load-alist: Hooks for Loadingafter-make-frame-functions: Creating Framesafter-revert-hook: Revertingafter-save-hook: Saving Buffersafter-string (overlay property): Overlay Propertiesall-christian-calendar-holidays: Holiday Customizingall-completions: Basic Completionall-hebrew-calendar-holidays: Holiday Customizingall-islamic-calendar-holidays: Holiday Customizingand: Combining Conditionsappend: Building Listsappend-to-file: Writing to Filesapply: Calling Functionsapply, and debugging: Internals of Debuggerappt-audible: Appt Customizingappt-delete-window-function: Appt Customizingappt-disp-window-function: Appt Customizingappt-display-duration: Appt Customizingappt-display-mode-line: Appt Customizingappt-message-warning-time: Appt Customizingappt-msg-window: Appt Customizingappt-visible: Appt Customizingapropos: Help Functionsaref: Array Functionsarith-error example: Handling Errorsarith-error in division: Arithmetic Operationsarrayp: Array Functionsaset: Array Functionsash: Bitwise Operationsasin: Math Functionsask-user-about-lock: File Locksask-user-about-supersession-threat: Modification Timeassoc: Association Listsassoc-default: Association Listsassoc-ignore-case: Text Comparisonassoc-ignore-representation: Text Comparisonassq: Association Listsassq-delete-all: Association Listsatan: Math Functionsatom: List-related Predicatesauto-coding-regexp-alist: Default Coding Systemsauto-fill-chars: Auto Fillingauto-fill-function: Auto Fillingauto-mode-alist: Auto Major Modeauto-raise-tool-bar-items: Tool Barauto-resize-tool-bar: Tool Barauto-save-default: Auto-Savingauto-save-file-format: Format Conversionauto-save-file-name-p: Auto-Savingauto-save-hook: Auto-Savingauto-save-interval: Auto-Savingauto-save-list-file-name: Auto-Savingauto-save-list-file-prefix: Auto-Savingauto-save-mode: Auto-Savingauto-save-timeout: Auto-Savingauto-save-visited-file-name: Auto-Savingback-to-indentation: Motion by Indentbacktrace: Internals of Debuggerbacktrace-debug: Internals of Debuggerbacktrace-frame: Internals of Debuggerbackup-buffer: Making Backupsbackup-by-copying: Rename or Copybackup-by-copying-when-linked: Rename or Copybackup-by-copying-when-mismatch: Rename or Copybackup-by-copying-when-privileged-mismatch: Rename or Copybackup-directory-alist: Making Backupsbackup-enable-predicate: Making Backupsbackup-file-name-p: Backup Namesbackup-inhibited: Making Backupsbackward-char: Character Motionbackward-delete-char-untabify: Deletionbackward-delete-char-untabify-method: Deletionbackward-list: List Motionbackward-prefix-chars: Motion and Syntaxbackward-sexp: List Motionbackward-to-indentation: Motion by Indentbackward-word: Word Motionbarf-if-buffer-read-only: Read Only Buffersbase64-decode-region: Base 64base64-decode-string: Base 64base64-encode-region: Base 64base64-encode-string: Base 64batch-byte-compile: Compilation Functionsbaud-rate: Terminal Outputbeep: Beepingbefore-change-functions: Change Hooksbefore-init-hook: Init Filebefore-make-frame-hook: Creating Framesbefore-revert-hook: Revertingbefore-string (overlay property): Overlay Propertiesbeginning-of-buffer: Buffer End Motionbeginning-of-defun: List Motionbeginning-of-defun-function: List Motionbeginning-of-line: Text Linesbitmap-spec-p: Face Attributesblink-matching-delay: Blinkingblink-matching-open: Blinkingblink-matching-paren: Blinkingblink-matching-paren-distance: Blinkingblink-paren-function: Blinkingbobp: Near Pointbold (face name): Standard Facesbold-italic (face name): Standard Facesbolp: Near Pointbool-vector-p: Bool-Vectorsboundp: Void Variablesbuffer-access-fontified-property: Lazy Propertiesbuffer-access-fontify-functions: Lazy Propertiesbuffer-auto-save-file-name: Auto-Savingbuffer-backed-up: Making Backupsbuffer-base-buffer: Indirect Buffersbuffer-disable-undo: Maintaining Undobuffer-display-table: Active Display Tablebuffer-display-time: Buffers and Windowsbuffer-enable-undo: Maintaining Undobuffer-end: Pointbuffer-file-coding-system: Encoding and I/Obuffer-file-format: Format Conversionbuffer-file-name: Buffer File Namebuffer-file-number: Buffer File Namebuffer-file-truename: Buffer File Namebuffer-file-type: MS-DOS File Typesbuffer-flush-undo: Maintaining Undobuffer-has-markers-at: Information from Markersbuffer-invisibility-spec: Invisible Textbuffer-list: The Buffer Listbuffer-local-variables: Creating Buffer-LocalBuffer-menu-mode-map: Standard Keymapsbuffer-modified-p: Buffer Modificationbuffer-modified-tick: Buffer Modificationbuffer-name: Buffer Namesbuffer-name-history: Minibuffer Historybuffer-offer-save: Killing Buffersbuffer-read-only: Read Only Buffersbuffer-saved-size: Auto-Savingbuffer-size: Pointbuffer-string: Buffer Contentsbuffer-substring: Buffer Contentsbuffer-substring-no-properties: Buffer Contentsbuffer-undo-list: Undobufferp: Buffer Basicsbury-buffer: The Buffer Listbutlast: List Elementsbyte-boolean-vars: Writing Emacs Primitivesbyte-code: Compilation Functionsbyte-code-function-p: What Is a Functionbyte-compile: Compilation Functionsbyte-compile-dynamic: Dynamic Loadingbyte-compile-dynamic-docstrings: Docs and Compilationbyte-compile-file: Compilation Functionsrequire: Named Featuresbyte-recompile-directory: Compilation Functionsbyte-to-position: Text RepresentationsC-M-x: Instrumentingc-mode-map: Standard Keymapsc-mode-syntax-table: Standard Syntax Tablescaar: List Elementscache-long-line-scans: Truncationcadr: List Elementscalendar-date-display-form: Date Display Formatcalendar-daylight-savings-ends: Daylight Savingscalendar-daylight-savings-ends-time: Daylight Savingscalendar-daylight-savings-starts: Daylight Savingscalendar-daylight-savings-starts-time: Daylight Savingscalendar-daylight-time-offset: Daylight Savingscalendar-holiday-marker: Calendar Customizingcalendar-holidays: Holiday Customizingcalendar-load-hook: Calendar Customizingcalendar-mark-today: Calendar Customizingcalendar-move-hook: Calendar Customizingcalendar-star-date: Calendar Customizingcalendar-time-display-form: Time Display Formatcalendar-today-marker: Calendar Customizingcall-interactively: Interactive Callcall-process: Synchronous Processescall-process-region: Synchronous Processescancel-debug-on-entry: Function Debuggingcancel-timer: Timerscapitalize: Case Conversioncapitalize-region: Case Changescapitalize-word: Case Changescar: List Elementscar-safe: List Elementscase-fold-search: Searching and Casecase-replace: Searching and Casecase-table-p: Case Tablescatch: Catch and Throwcategory (overlay property): Overlay Propertiescategory (text property): Special Propertiescategory-docstring: Categoriescategory-set-mnemonics: Categoriescategory-table: Categoriescategory-table-p: Categoriescdar: List Elementscddr: List Elementscdr: List Elementscdr-safe: List Elementsceiling: Numeric Conversionschange-major-mode-hook: Creating Buffer-Localchar-after: Near Pointchar-before: Near Pointchar-category-set: Categorieschar-charset: Character Setschar-equal: Text Comparisonchar-or-string-p: Predicates for Stringschar-syntax: Syntax Table Functionschar-table-extra-slot: Char-Tableschar-table-p: Char-Tableschar-table-parent: Char-Tableschar-table-range: Char-Tableschar-table-subtype: Char-Tableschar-to-string: String Conversionchar-valid-p: Character Codeschar-width: Widthcharacter quote: Syntax Class Tablecharset-bytes: Chars and Bytescharset-dimension: Chars and Bytescharset-list: Character Setscharset-plist: Character Setscharsetp: Character Setscheck-coding-system: Lisp and Coding Systemscheckdoc-minor-mode: Documentation Tipschristian-holidays: Holiday Customizingcl: Lisp Historyeq: Comparison of Numbersunion, intersection: Sets And Liststhrow in Emacs: Catch and Throwrplaca vrs setcar: Modifying Listsset local: Setting Variablescl-specs.el: Instrumentingcl.el (Edebug): Instrumentingclear-abbrev-table: Abbrev Tablesclear-face-cache: Font Selectionclear-image-cache: Image Cacheclear-this-command-keys: Command Loop Infoclear-visited-file-modtime: Modification Timeclose parenthesis character: Syntax Class Tableclrhash: Hash Accesscoding-system-change-eol-conversion: Lisp and Coding Systemscoding-system-change-text-conversion: Lisp and Coding Systemscoding-system-for-read: Specifying Coding Systemscoding-system-for-write: Specifying Coding Systemscoding-system-get: Coding System Basicscoding-system-list: Lisp and Coding Systemscoding-system-p: Lisp and Coding Systemscolor-defined-p: Color Namescolor-gray-p: Color Namescolor-supported-p: Color Namescolor-values: Color Namescombine-after-change-calls: Change Hookscommand-debug-status: Internals of Debuggercommand-execute: Interactive Callcommand-history: Command Historycommand-history-map: Standard Keymapscommand-line: Command-Line Argumentscommand-line-args: Command-Line Argumentscommand-line-functions: Command-Line Argumentscommand-line-processed: Command-Line Argumentscommand-switch-alist: Command-Line Argumentscommandp: Interactive Callcommandp example: High-Level Completioncomment ender: Syntax Class Tablecomment starter: Syntax Class Tablecompare-buffer-substrings: Comparing Textcompare-strings: Text Comparisoncompare-window-configurations: Window Configurationscompile-defun: Compilation Functionscompleting-read: Minibuffer Completioncompletion-auto-help: Completion Commandscompletion-ignore-case: Basic Completioncompletion-ignored-extensions: File Name Completioncompute-motion: Screen Linesconcat: Creating Stringscond: Conditionalscondition-case: Handling Errorscons: Building Listscons-cells-consed: Memory Usageconsp: List-related Predicatesconstrain-to-field: Fieldscontinue-process: Signals to ProcessesControl-X-prefix: Prefix Keysconvert-standard-filename: Standard File Namescoordinates-in-window-p: Coordinates and Windowscopy-alist: Association Listscopy-category-table: Categoriescopy-face: Face Functionscopy-file: Changing Filescopy-hash-table: Other Hashcopy-keymap: Creating Keymapscopy-marker: Creating Markerscopy-region-as-kill: Kill Functionscopy-sequence: Sequence Functionscopy-syntax-table: Syntax Table Functionscos: Math Functionscount-lines: Text Linescount-loop: A Sample Function Descriptioncount-screen-lines: Screen Linescreate-file-buffer: Subroutines of Visitingcreate-fontset-from-fontset-spec: Fontsetscreate-glyph: Glyphscreate-image: Defining Imagesctl-arrow: Usual Displayctl-x-4-map: Prefix Keysctl-x-5-map: Prefix Keysctl-x-map: Prefix Keyscurrent-buffer: Current Buffercurrent-case-table: Case Tablescurrent-column: Columnscurrent-fill-column: Marginscurrent-frame-configuration: Frame Configurationscurrent-global-map: Active Keymapscurrent-indentation: Primitive Indentcurrent-input-method: Input Methodscurrent-input-mode: Input Modescurrent-justification: Fillingcurrent-kill: Low-Level Kill Ringcurrent-left-margin: Marginscurrent-local-map: Active Keymapscurrent-message: The Echo Areacurrent-minor-mode-maps: Active Keymapscurrent-prefix-arg: Prefix Command Argumentscurrent-time: Time of Daycurrent-time-string: Time of Daycurrent-time-zone: Time of Daycurrent-window-configuration: Window Configurationscursor-in-echo-area: The Echo Areacursor-type: Window Frame Parameterscust-print: Printing in Edebugcustom-add-option: Variable Definitionsdata-directory: Help Functionsdeactivate-mark: The Markdeactivate-mark-hook: The Markdebug: Invoking the Debuggerdebug-ignored-errors: Error Debuggingdebug-on-entry: Function Debuggingdebug-on-error: Error Debuggingdebug-on-error use: Processing of Errorsdebug-on-next-call: Internals of Debuggerdebug-on-quit: Infinite Loopsdebug-on-signal: Error Debuggingdebugger: Internals of Debuggerdebugger-mode-map: Standard Keymapsdecode-coding-region: Explicit Encodingdecode-coding-string: Explicit Encodingdecode-time: Time Conversiondef-edebug-spec: Instrumenting Macro Callsdefadvice: Defining Advicedefalias: Defining Functionsdefault (face name): Standard Facesdefault-abbrev-mode: Abbrev Modedefault-boundp: Default Valuedefault-buffer-file-type: MS-DOS File Typesdefault-case-fold-search: Searching and Casedefault-ctl-arrow: Usual Displaydefault-directory: File Name Expansiondefault-enable-multibyte-characters: Text Representationsdefault-file-modes: Changing Filesdefault-fill-column: Marginsdefault-frame-alist: Initial Parametersdefault-header-line-format: Header Linesdefault-input-method: Input Methodsdefault-justification: Fillingdefault-major-mode: Auto Major Modedefault-minibuffer-frame: Minibuffers and Framesdefault-mode-line-format: Mode Line Variablesdefault-process-coding-system: Default Coding Systemsdefault-text-properties: Examining Propertiesdefault-truncate-lines: Truncationdefault-value: Default Valuedefconst: Defining Variablesdefcustom: Variable Definitionsdefface: Defining Facesdefgroup: Group Definitionsdefimage: Defining Imagesdefine-abbrev: Defining Abbrevsdefine-abbrev-table: Abbrev Tablesdefine-category: Categoriesdefine-derived-mode: Derived Modesdefine-hash-table-test: Defining Hashdefine-key: Changing Key Bindingsdefine-key-after: Modifying Menusdefine-logical-name: Changing Filesdefine-minor-mode: Defining Minor Modesdefine-prefix-command: Prefix Keysdefined-colors: Color Namesdefining-kbd-macro: Keyboard Macrosdefmacro: Defining Macrosdefsubst: Inline Functionsdefun: Defining Functionsdefun-prompt-regexp: List Motiondefvar: Defining Variablesdelete: Sets And Listsdelete-and-extract-region: Deletiondelete-auto-save-file-if-necessary: Auto-Savingdelete-auto-save-files: Auto-Savingdelete-backward-char: Deletiondelete-blank-lines: User-Level Deletiondelete-char: Deletiondelete-directory: Create/Delete Dirsdelete-exited-processes: Deleting Processesdelete-field: Fieldsdelete-file: Changing Filesdelete-frame: Deleting Framesdelete-frame event: Misc Eventsdelete-frame-hook: Deleting Framesdelete-horizontal-space: User-Level Deletiondelete-indentation: User-Level Deletiondelete-minibuffer-contents: Minibuffer Miscdelete-old-versions: Numbered Backupsdelete-other-windows: Deleting Windowsdelete-overlay: Managing Overlaysdelete-process: Deleting Processesdelete-region: Deletiondelete-to-left-margin: Marginsdelete-window: Deleting Windowsdelete-windows-on: Deleting Windowsdelq: Sets And Listsdescribe-bindings: Scanning Keymapsdescribe-buffer-case-table: Case Tablesdescribe-categories: Categoriesdescribe-current-display-table: Display Table Formatdescribe-display-table: Display Table Formatdescribe-mode: Mode Helpdescribe-prefix-bindings: Help Functionsdetect-coding-region: Lisp and Coding Systemsdetect-coding-string: Lisp and Coding Systemsdiary-anniversary: Sexp Diary Entriesdiary-astro-day-number: Sexp Diary Entriesdiary-cyclic: Sexp Diary Entriesdiary-date: Sexp Diary Entriesdiary-date-forms: Diary Customizingdiary-day-of-year: Sexp Diary Entriesdiary-display-hook: Fancy Diary Displaydiary-entry-marker: Calendar Customizingdiary-float: Sexp Diary Entriesdiary-french-date: Sexp Diary Entriesdiary-hebrew-date: Sexp Diary Entriesdiary-islamic-date: Sexp Diary Entriesdiary-iso-date: Sexp Diary Entriesdiary-julian-date: Sexp Diary Entriesdiary-list-include-blanks: Fancy Diary Displaydiary-mayan-date: Sexp Diary Entriesdiary-omer: Sexp Diary Entriesdiary-parasha: Sexp Diary Entriesdiary-phases-of-moon: Sexp Diary Entriesdiary-remind: Sexp Diary Entriesdiary-rosh-hodesh: Sexp Diary Entriesdiary-sabbath-candles: Sexp Diary Entriesdiary-sunrise-sunset: Sexp Diary Entriesdiary-yahrzeit: Sexp Diary Entriesdigit-argument: Prefix Command Argumentsding: Beepingdirectory-abbrev-alist: Directory Namesdirectory-file-name: Directory Namesdirectory-files: Contents of Directoriesdired-kept-versions: Numbered Backupsdired-mode-map: Standard Keymapsdisable-command: Disabling Commandsdisable-point-adjustment: Adjusting Pointdisabled: Disabling Commandsdisabled-command-hook: Disabling Commandsdisassemble: Disassemblydiscard-input: Event Input Miscdisplay (overlay property): Overlay Propertiesdisplay (text property): Display Propertydisplay (text property): Special Propertiesdisplay-backing-store: Display Feature Testingdisplay-buffer: Choosing Windowdisplay-buffer-function: Choosing Windowdisplay-buffer-reuse-frames: Choosing Windowdisplay-color-cells: Display Feature Testingdisplay-color-p: Display Feature Testingdisplay-completion-list: Completion Commandsdisplay-graphic-p: Display Feature Testingdisplay-grayscale-p: Display Feature Testingdisplay-images-p: Display Feature Testingdisplay-message-or-buffer: The Echo Areadisplay-mm-height: Display Feature Testingdisplay-mm-width: Display Feature Testingdisplay-mouse-p: Display Feature Testingdisplay-pixel-height: Display Feature Testingdisplay-pixel-width: Display Feature Testingdisplay-planes: Display Feature Testingdisplay-popup-menus-p: Display Feature Testingdisplay-save-under: Display Feature Testingdisplay-screens: Display Feature Testingdisplay-selections-p: Display Feature Testingdisplay-table-slot: Display Table Formatdisplay-visual-class: Display Feature Testingdo-auto-save: Auto-Savingdoc-directory: Accessing Documentationdocumentation: Accessing Documentationdocumentation-property: Accessing Documentationdolist: Iterationdotimes: Iterationdouble-click-fuzz: Repeat Eventsdouble-click-time: Repeat Eventsdown-list: List Motiondowncase: Case Conversiondowncase-region: Case Changesdowncase-word: Case Changeslookup-key: Key Sequence Inputdrag-n-drop event: Misc Eventsdump-emacs: Building Emacseasy-mmode-define-minor-mode: Defining Minor Modesecho-area-clear-hook: The Echo Areaecho-keystrokes: The Echo Areaedebug: Source Breakpointsedebug-all-defs: Edebug Optionsedebug-all-forms: Edebug Optionsedebug-continue-kbd-macro: Edebug Optionsedebug-display-freq-count: Coverage Testingedebug-eval-top-level-form: Instrumentingedebug-global-break-condition: Edebug Optionsedebug-initial-mode: Edebug Optionsedebug-on-error: Edebug Optionsedebug-on-quit: Edebug Optionsedebug-print-circle: Printing in Edebugedebug-print-length: Printing in Edebugedebug-print-level: Printing in Edebugedebug-print-trace-after: Trace Bufferedebug-print-trace-before: Trace Bufferedebug-save-displayed-buffer-points: Edebug Optionsedebug-save-windows: Edebug Optionsedebug-set-global-break-condition: Global Break Conditionedebug-setup-hook: Edebug Optionsedebug-test-coverage: Edebug Optionsedebug-trace: Edebug Optionsedebug-trace: Trace Bufferedebug-tracing: Trace Bufferedebug-unwrap: Specification Listedit-abbrevs-map: Standard Keymapsedit-and-eval-command: Object from Minibufferedit-tab-stops-map: Standard Keymapselectric-buffer-menu-mode-map: Standard Keymapselectric-future-map: A Sample Variable Descriptionelectric-history-map: Standard Keymapselt: Sequence Functionsemacs-build-time: Version Infoemacs-lisp-mode-map: Standard Keymapsemacs-lisp-mode-syntax-table: Standard Syntax Tablesemacs-major-version: Version Infoemacs-minor-version: Version Infoemacs-pid: System Environmentemacs-startup-hook: Init Fileemacs-version: Version InfoEMACSLOADPATH environment variable: Library Searchenable-command: Disabling Commandsenable-flow-control: Flow Controlenable-flow-control-on: Flow Controlenable-local-eval: File Local Variablesenable-local-variables: File Local Variablesenable-multibyte-characters: Text Representationsenable-recursive-minibuffers: Minibuffer Miscencode-coding-region: Explicit Encodingencode-coding-string: Explicit Encodingencode-time: Time Conversionend-of-buffer: Buffer End Motionend-of-defun: List Motionend-of-defun-function: List Motionend-of-file: Input Functionsend-of-line: Text Linesenlarge-window: Resizing Windowsenlarge-window-horizontally: Resizing Windowseobp: Near Pointeolp: Near Pointeq: Equality Predicatesequal: Equality Predicateserase-buffer: Deletionerror: Signaling Errorserror in debug: Invoking the Debuggererror-conditions: Error Symbolserror-message-string: Handling Errorsesc-map: Prefix KeysESC-prefix: Prefix Keysescape: Syntax Class Tableeval: Evaleval, and debugging: Internals of Debuggereval-after-load: Hooks for Loadingeval-and-compile: Eval During Compileeval-current-buffer: Evaleval-current-buffer (Edebug): Instrumentingeval-defun (Edebug): Instrumentingeval-expression (Edebug): Instrumentingeval-minibuffer: Object from Minibuffereval-region: Evaleval-region (Edebug): Instrumentingeval-when-compile: Eval During Compileevaporate (overlay property): Overlay Propertieseven-window-heights: Choosing Windowevent-basic-type: Classifying Eventsevent-click-count: Repeat Eventsevent-convert-list: Classifying Eventsevent-end: Accessing Eventsevent-modifiers: Classifying Eventsevent-start: Accessing Eventseventp: Input Eventsinteractive form: Using Interactiveinteractive: Interactive Examplesexec-directory: Subprocess Creationexec-path: Subprocess Creationexecute-extended-command: Interactive Callexecute-kbd-macro: Keyboard Macrosexecuting-macro: Keyboard Macrosexit: Recursive Editingexit-minibuffer: Minibuffer Miscexit-recursive-edit: Recursive Editingexp: Math Functionsexpand-abbrev: Abbrev Expansionexpand-file-name: File Name Expansionexpression prefix: Syntax Class Tableexpt: Math Functionsextended-command-history: Minibuffer Historyextra-keyboard-modifiers: Translating Inputface (overlay property): Overlay Propertiesface (text property): Special Propertiesface-attribute: Attribute Functionsface-background: Attribute Functionsface-bold-p: Attribute Functionsface-default-registry: Font Selectionface-differs-from-default-p: Face Functionsface-documentation: Face Functionsface-equal: Face Functionsface-font: Attribute Functionsface-font-family-alternatives: Font Selectionface-font-registry-alternatives: Font Selectionface-font-selection-order: Font Selectionface-foreground: Attribute Functionsface-id: Face Functionsface-inverse-video-p: Attribute Functionsface-italic-p: Attribute Functionsface-list: Face Functionsface-stipple: Attribute Functionsface-underline-p: Attribute Functionsfacemenu-background-menu: Standard Keymapsfacemenu-face-menu: Standard Keymapsfacemenu-foreground-menu: Standard Keymapsfacemenu-indentation-menu: Standard Keymapsfacemenu-justification-menu: Standard Keymapsfacemenu-keymap: Prefix Keysfacemenu-menu: Standard Keymapsfacemenu-special-menu: Standard Keymapsfacep: Facesfancy-diary-display: Fancy Diary Displayfboundp: Function Cellsfceiling: Rounding Operations-unload-hook: Unloadingfeaturep: Named Featuresfetch-bytecode: Dynamic Loadingffloor: Rounding Operationsfield (text property): Special Propertiesfield-beginning: Fieldsfield-end: Fieldsfield-string: Fieldsfield-string-no-properties: Fieldsfile-accessible-directory-p: Testing Accessibilityfile-already-exists: Changing Filesfile-attributes: File Attributesfile-chase-links: Truenamesfile-coding-system-alist: Default Coding Systemsfile-directory-p: Kinds of Filesfile-error: How Programs Do Loadingfile-executable-p: Testing Accessibilityfile-exists-p: Testing Accessibilityfile-expand-wildcards: Contents of Directoriesfile-local-copy: Magic File Namesfile-locked: File Locksfile-locked-p: File Locksfile-modes: File Attributesfile-name-absolute-p: Relative File Namesfile-name-all-completions: File Name Completionfile-name-all-versions: Contents of Directoriesfile-name-as-directory: Directory Namesfile-name-buffer-file-type-alist: MS-DOS File Typesfile-name-completion: File Name Completionfile-name-directory: File Name Componentsfile-name-extension: File Name Componentsfile-name-history: Minibuffer Historyfile-name-nondirectory: File Name Componentsfile-name-sans-extension: File Name Componentsfile-name-sans-versions: File Name Componentsfile-newer-than-file-p: Testing Accessibilityfile-newest-backup: Backup Namesfile-nlinks: File Attributesfile-ownership-preserved-p: Testing Accessibilityfile-precious-flag: Saving Buffersfile-readable-p: Testing Accessibilityfile-regular-p: Kinds of Filesfile-relative-name: File Name Expansionfile-supersession: Modification Timefile-symlink-p: Kinds of Filesfile-truename: Truenamesfile-writable-p: Testing Accessibilityfill-column: Marginsfill-context-prefix: Adaptive Fillfill-individual-paragraphs: Fillingfill-individual-varying-indent: Fillingfill-nobreak-predicate: Marginsfill-paragraph: Fillingfill-paragraph-function: Fillingfill-prefix: Marginsfill-region: Fillingfill-region-as-paragraph: Fillingfillarray: Array Functionsfind-backup-file-name: Backup Namesfind-charset-region: Scanning Charsetsfind-charset-string: Scanning Charsetsfind-coding-systems-for-charsets: Lisp and Coding Systemsfind-coding-systems-region: Lisp and Coding Systemsfind-coding-systems-string: Lisp and Coding Systemsfind-file: Visiting Functionsfind-file-hooks: Visiting Functionsfind-file-name-handler: Magic File Namesfind-file-noselect: Visiting Functionsfind-file-not-found-hooks: Visiting Functionsfind-file-other-window: Visiting Functionsfind-file-read-only: Visiting Functionsfind-file-wildcards: Visiting Functionsfind-image: Defining Imagesfind-operation-coding-system: Default Coding Systemsfirst-change-hook: Change Hooksfixed-pitch (face name): Standard Facesfixup-whitespace: User-Level Deletionfloat: Numeric Conversionsfloat-time: Time of Dayfloatp: Predicates on Numbersfloats-consed: Memory Usagefloor: Numeric Conversionsfmakunbound: Function Cellsfocus-follows-mouse: Input Focusfollowing-char: Near Pointfont-list-limit: Font Lookupfont-lock-beginning-of-syntax-function: Other Font Lock Variablesfont-lock-builtin-face: Faces for Font Lockfont-lock-comment-face: Faces for Font Lockfont-lock-constant-face: Faces for Font Lockfont-lock-defaults: Font Lock Basicsfont-lock-function-name-face: Faces for Font Lockfont-lock-keyword-face: Faces for Font Lockfont-lock-keywords: Search-based Fontificationfont-lock-keywords-case-fold-search: Other Font Lock Variablesfont-lock-keywords-only: Other Font Lock Variablesfont-lock-mark-block-function: Other Font Lock Variablesfont-lock-string-face: Faces for Font Lockfont-lock-syntactic-keywords: Syntactic Font Lockfont-lock-syntax-table: Other Font Lock Variablesfont-lock-type-face: Faces for Font Lockfont-lock-variable-name-face: Faces for Font Lockfont-lock-warning-face: Faces for Font Lockfontification-functions: Auto Facesfontified (text property): Special Propertiesfoo: A Sample Function Descriptionfor: Argument Evaluationforce-mode-line-update: Mode Line Formatformat: Formatting Stringsformat-alist: Format Conversionformat-find-file: Format Conversionformat-insert-file: Format Conversionformat-time-string: Time Conversionformat-write-file: Format Conversionforward-char: Character Motionforward-comment: Parsing Expressionsforward-line: Text Linesforward-list: List Motionforward-sexp: List Motionforward-to-indentation: Motion by Indentforward-word: Word Motionframe-background-mode: Defining Facesframe-char-height: Size and Positionframe-char-width: Size and Positionframe-first-window: Frames and Windowsframe-height: Size and Positionframe-list: Finding All Framesframe-live-p: Deleting Framesframe-parameter: Parameter Accessframe-parameters: Parameter Accessframe-pixel-height: Size and Positionframe-pixel-width: Size and Positionframe-selected-window: Frames and Windowsframe-title-format: Frame Titlesframe-visible-p: Visibility of Framesframe-width: Size and Positionframep: Framesfringe (face name): Standard Facesfround: Rounding Operationsfset: Function Cellsftp-login: Cleanupsftruncate: Rounding Operationsfuncall: Calling Functionsfuncall, and debugging: Internals of Debuggerfunction: Anonymous Functionsfunction-key-map: Translating Inputfunctionp: What Is a Functionfundamental-mode: Auto Major Modefundamental-mode-abbrev-table: Standard Abbrev Tablesfundamental-mode-map: Standard Keymapsgap-position: Buffer Gapgap-size: Buffer Gapgarbage-collect: Garbage Collectiongarbage-collection-messages: Garbage Collectiongc-cons-threshold: Garbage Collectiongeneral-holidays: Holiday Customizinggenerate-new-buffer: Creating Buffersgenerate-new-buffer-name: Buffer Namesgeneric comment delimiter: Syntax Class Tablegeneric string delimiter: Syntax Class Tableget: Symbol Plistsget-buffer: Buffer Namesget-buffer-create: Creating Buffersget-buffer-process: Process Buffersget-buffer-window: Buffers and Windowsget-buffer-window-list: Buffers and Windowsget-char-property: Examining Propertiesget-file-buffer: Buffer File Nameget-file-char: Input Streamsget-largest-window: Selecting Windowsget-lru-window: Selecting Windowsget-process: Process Informationget-register: Registersget-text-property: Examining Propertiesget-unused-category: Categoriesget-window-with-predicate: Selecting Windowsgetenv: System Environmentgethash: Hash Accessglobal-abbrev-table: Standard Abbrev Tablesglobal-disable-point-adjustment: Adjusting Pointglobal-key-binding: Functions for Key Lookupglobal-map: Active Keymapsglobal-mode-string: Mode Line Variablesglobal-set-key: Key Binding Commandsglobal-unset-key: Key Binding Commandsglyph-table: Glyphsgoto-char: Character Motiongoto-line: Text Lineshack-local-variables: File Local Variableshandle-switch-frame: Input Focushash-table-count: Other Hashhash-table-p: Other Hashhash-table-rehash-size: Other Hashhash-table-rehash-threshold: Other Hashhash-table-size: Other Hashhash-table-test: Other Hashhash-table-weakness: Other Hashheader-line (face name): Standard Facesheader-line prefix key: Key Sequence Inputheader-line-format: Header Lineshebrew-holidays: Holiday Customizinghelp-char: Help Functionshelp-command: Help Functionshelp-echo (text property): Overlay Propertieshelp-echo (text property): Special Propertieshelp-event-list: Help Functionshelp-form: Help Functionshelp-map: Help FunctionsHelper-describe-bindings: Help FunctionsHelper-help: Help FunctionsHelper-help-map: Standard Keymapshighlight (face name): Standard Facesholidays-in-diary-buffer: Diary CustomizingHOME environment variable: Subprocess Creationhorizontal-scroll-bar prefix key: Key Sequence Inputicon-title-format: Frame Titlesiconify-frame: Visibility of Framesiconify-frame event: Misc Eventsidentity: Calling Functionsif: Conditionalsignore: Calling Functionsignored-local-variables: File Local Variablesimage-cache-eviction-delay: Image Cacheimage-mask-p: Image Descriptorsimage-size: Showing Imagesimage-types: Imagesimenu-case-fold-search: Imenuimenu-create-index-function: Imenuimenu-extract-index-name-function: Imenuimenu-generic-expression: Imenuimenu-index-alist: Imenuimenu-prev-index-position-function: Imenuimenu-syntax-alist: Imenuprogn: Sequencinginc: Simple Macroinclude-other-diary-files: Fancy Diary Displayindent-according-to-mode: Mode-Specific Indentindent-code-rigidly: Region Indentindent-for-tab-command: Mode-Specific Indentindent-line-function: Mode-Specific Indentindent-region: Region Indentindent-region-function: Region Indentindent-relative: Relative Indentindent-relative-maybe: Relative Indentindent-rigidly: Region Indentindent-tabs-mode: Primitive Indentindent-to: Primitive Indentindent-to-left-margin: Marginsindicate-empty-lines: Usual Displayindirect-function: Function IndirectionInfo-edit-map: Standard KeymapsInfo-mode-map: Standard Keymapsinherit: Syntax Class Tableinhibit-default-init: Init Fileinhibit-eol-conversion: Specifying Coding Systemsinhibit-field-text-motion: Word Motioninhibit-file-name-handlers: Magic File Namesinhibit-file-name-operation: Magic File Namesinhibit-modification-hooks: Change Hooksinhibit-point-motion-hooks: Special Propertiesinhibit-quit: Quittinginhibit-read-only: Read Only Buffersinhibit-startup-echo-area-message: Startup Summaryinhibit-startup-message: Startup Summaryinit-file-user: User Identificationinitial-calendar-window-hook: Calendar Customizinginitial-frame-alist: Initial Parametersinitial-major-mode: Auto Major Modeinput-method-alist: Input Methodsinput-method-function: Invoking the Input Methodinput-pending-p: Event Input Miscinsert: Insertioninsert-abbrev-table-description: Abbrev Tablesinsert-and-inherit: Sticky Propertiesinsert-before-markers: Insertioninsert-before-markers-and-inherit: Sticky Propertiesinsert-behind-hooks (overlay property): Overlay Propertiesinsert-behind-hooks (text property): Special Propertiesinsert-buffer: Commands for Insertioninsert-buffer-substring: Insertioninsert-char: Insertioninsert-default-directory: Reading File Namesinsert-directory: Contents of Directoriesinsert-directory-program: Contents of Directoriesinsert-file-contents: Reading from Filesinsert-file-contents-literally: Reading from Filesinsert-hebrew-diary-entry: Hebrew/Islamic Entriesinsert-image: Showing Imagesinsert-in-front-hooks (overlay property): Overlay Propertiesinsert-in-front-hooks (text property): Special Propertiesinsert-islamic-diary-entry: Hebrew/Islamic Entriesinsert-monthly-hebrew-diary-entry: Hebrew/Islamic Entriesinsert-monthly-islamic-diary-entry: Hebrew/Islamic Entriesinsert-register: Registersinsert-yearly-hebrew-diary-entry: Hebrew/Islamic Entriesinsert-yearly-islamic-diary-entry: Hebrew/Islamic Entriesinstallation-directory: System Environmentintangible (overlay property): Overlay Propertiesintangible (text property): Special Propertiesinteger-or-marker-p: Predicates on Markersintegerp: Predicates on Numbersinteractive: Using Interactiveinteractive, examples of using: Interactive Examplesinteractive-form: Using Interactiveinteractive-p: Interactive Callintern: Creating Symbolsintern-soft: Creating Symbolsinterpreter-mode-alist: Auto Major Modeinterprogram-cut-function: Low-Level Kill Ringinterprogram-paste-function: Low-Level Kill Ringinterrupt-process: Signals to Processesintervals-consed: Memory Usageinvalid-function: Function Indirectioninvalid-read-syntax: Printed Representationinvalid-regexp: Regexp Backslashinverse-video: Inverse Videoinvert-face: Attribute Functionsinvisible (overlay property): Overlay Propertiesinvisible (text property): Special Propertiesinvocation-directory: System Environmentinvocation-name: System Environmentisearch-mode-map: Standard Keymapsislamic-holidays: Holiday Customizingitalic (face name): Standard Facesjust-one-space: User-Level Deletionjustify-current-line: Fillingkbd-macro-termination-hook: Keyboard Macroskept-new-versions: Numbered Backupskept-old-versions: Numbered Backupskey-binding: Functions for Key Lookupkey-description: Describing Characterskey-translation-map: Translating Inputkeyboard-coding-system: Terminal I/O Encodingkeyboard-quit: Quittingkeyboard-translate: Translating Inputkeyboard-translate-table: Translating Inputkeymap (overlay property): Overlay Propertieskeymap (text property): Special Propertieskeymap-parent: Inheritance and Keymapskeymapp: Format of Keymapskeywordp: Constant Variableskill-all-local-variables: Creating Buffer-Localkill-append: Low-Level Kill Ringkill-buffer: Killing Bufferskill-buffer-hook: Killing Bufferskill-buffer-query-functions: Killing Bufferskill-emacs: Killing Emacskill-emacs-hook: Killing Emacskill-emacs-query-functions: Killing Emacskill-local-variable: Creating Buffer-Localkill-new: Low-Level Kill Ringkill-process: Signals to Processeskill-read-only-ok: Kill Functionskill-region: Kill Functionskill-ring: Internals of Kill Ringkill-ring-max: Internals of Kill Ringkill-ring-yank-pointer: Internals of Kill Ringlambda in debug: Invoking the Debuggerlambda in keymap: Key Lookuplast: List Elementslast-abbrev: Abbrev Expansionlast-abbrev-location: Abbrev Expansionlast-abbrev-text: Abbrev Expansionlast-coding-system-used: Encoding and I/Olast-command: Command Loop Infolast-command-char: Command Loop Infolast-command-event: Command Loop Infolast-event-frame: Command Loop Infolast-input-char: Event Input Misclast-input-event: Event Input Misclast-kbd-macro: Keyboard Macroslast-nonmenu-event: Command Loop Infolast-prefix-arg: Prefix Command Argumentsleft-margin: Marginsleft-margin-width: Display Marginslength: Sequence Functionslet: Local Variableslet*: Local Variablesline-beginning-position: Text Linesline-end-position: Text Linesline-move-ignore-invisible: Invisible Textlisp-interaction-mode-map: Standard Keymapslisp-mode-abbrev-table: Standard Abbrev Tableslisp-mode-map: Standard Keymapslist: Building Listslist-buffers-directory: Buffer File Namelist-diary-entries-hook: Fancy Diary Displaylist-hebrew-diary-entries: Hebrew/Islamic Entrieslist-islamic-diary-entries: Hebrew/Islamic Entrieslist-processes: Process Informationlistify-key-sequence: Event Input Misclistp: List-related Predicatesln: Changing Filesload: How Programs Do Loadingload-average: System Environmentload-file: How Programs Do Loadingload-history: Unloadingload-in-progress: How Programs Do Loadingload-library: How Programs Do Loadingload-path: Library Searchload-read-function: How Programs Do Loadingloadhist-special-hooks: Unloadinglocal-abbrev-table: Standard Abbrev Tableslocal-holidays: Holiday Customizinglocal-key-binding: Functions for Key Lookuplocal-map (overlay property): Overlay Propertieslocal-map (text property): Special Propertieslocal-set-key: Key Binding Commandslocal-unset-key: Key Binding Commandslocal-variable-p: Creating Buffer-Locallocal-write-file-hooks: Saving Bufferslocale-coding-system: Localeslocate-library: Library Searchlock-buffer: File Lockslog: Math Functionslog10: Math Functionslogand: Bitwise Operationslogb: Float Basicslogior: Bitwise Operationslognot: Bitwise Operationslogxor: Bitwise Operationslooking-at: Regexp Searchlookup-key: Functions for Key Lookuplower-frame: Raising and Loweringlsh: Bitwise Operationsmacroexpand: Expansionmail-host-address: System Environmentmajor-mode: Mode Helpmake-abbrev-table: Abbrev Tablesmake-auto-save-file-name: Auto-Savingmake-backup-file-name: Backup Namesmake-backup-file-name-function: Making Backupsmake-backup-files: Making Backupsmake-bool-vector: Bool-Vectorsmake-byte-code: Byte-Code Objectsmake-category-set: Categoriesmake-category-table: Categoriesmake-char: Splitting Charactersmake-char-table: Char-Tablesmake-directory: Create/Delete Dirsmake-display-table: Display Table Formatmake-face: Face Functionsmake-frame: Creating Framesmake-frame-invisible: Visibility of Framesmake-frame-on-display: Multiple Displaysmake-frame-visible: Visibility of Framesmake-frame-visible event: Misc Eventsmake-hash-table: Creating Hashmake-help-screen: Help Functionsmake-indirect-buffer: Indirect Buffersmake-keymap: Creating Keymapsmake-list: Building Listsmake-local-hook: Hooksmake-local-variable: Creating Buffer-Localmake-marker: Creating Markersmake-overlay: Managing Overlaysmake-sparse-keymap: Creating Keymapsmake-string: Creating Stringsmake-symbol: Creating Symbolsmake-symbolic-link: Changing Filesmake-syntax-table: Syntax Table Functionsmake-temp-file: Unique File Namesmake-temp-name: Unique File Namesmake-translation-table: Translation of Charactersmake-variable-buffer-local: Creating Buffer-Localmake-variable-frame-local: Frame-Local Variablesmake-vector: Vector Functionsmakehash: Creating Hashmakunbound: Void Variablesmap-char-table: Char-Tablesmap-y-or-n-p: Multiple Queriesmapatoms: Creating Symbolsmapc: Mapping Functionsmapcar: Mapping Functionsmapconcat: Mapping Functionsmaphash: Hash Accessmark: The Markmark-active: The Markmark-diary-entries-hook: Fancy Diary Displaymark-diary-entries-in-calendar: Calendar Customizingmark-even-if-inactive: The Markmark-hebrew-diary-entries: Hebrew/Islamic Entriesmark-holidays-in-calendar: Calendar Customizingmark-included-diary-files: Fancy Diary Displaymark-islamic-diary-entries: Hebrew/Islamic Entriesmark-marker: The Markmark-ring: The Markmark-ring-max: The Markmarker-buffer: Information from Markersmarker-insertion-type: Marker Insertion Typesmarker-position: Information from Markersmarkerp: Predicates on Markersmatch-beginning: Simple Match Datamatch-data: Entire Match Datamatch-end: Simple Match Datamatch-string: Simple Match Datamatch-string-no-properties: Simple Match Datamax: Comparison of Numbersmax-lisp-eval-depth: Evalmax-specpdl-size: Local Variablesmd5: MD5 Checksummember: Sets And Listsmember-ignore-case: Sets And Listsmemory-limit: Garbage Collectionmemq: Sets And Listsmenu-bar prefix key: Key Sequence Inputmenu-bar-edit-menu: Standard Keymapsmenu-bar-files-menu: Standard Keymapsmenu-bar-final-items: Menu Barmenu-bar-help-menu: Standard Keymapsmenu-bar-mule-menu: Standard Keymapsmenu-bar-search-menu: Standard Keymapsmenu-bar-tools-menu: Standard Keymapsmenu-bar-update-hook: Menu Barmenu-item: Extended Menu Itemsmenu-prompt-more-char: Keyboard Menusmessage: The Echo Areamessage-box: The Echo Areamessage-log-max: The Echo Areamessage-or-box: The Echo Areamessage-truncate-lines: The Echo Areameta-prefix-char: Functions for Key Lookupmin: Comparison of Numbersminibuffer-allow-text-properties: Text from Minibufferminibuffer-auto-raise: Raising and Loweringminibuffer-complete: Completion Commandsminibuffer-complete-and-exit: Completion Commandsminibuffer-complete-word: Completion Commandsminibuffer-completion-confirm: Completion Commandsminibuffer-completion-help: Completion Commandsminibuffer-completion-predicate: Completion Commandsminibuffer-completion-table: Completion Commandsminibuffer-contents: Minibuffer Miscminibuffer-contents-no-properties: Minibuffer Miscminibuffer-depth: Minibuffer Miscminibuffer-exit-hook: Minibuffer Miscminibuffer-frame-alist: Initial Parametersminibuffer-help-form: Minibuffer Miscminibuffer-history: Minibuffer Historyminibuffer-local-completion-map: Completion Commandsminibuffer-local-map: Text from Minibufferminibuffer-local-must-match-map: Completion Commandsminibuffer-local-ns-map: Text from Minibufferminibuffer-prompt: Minibuffer Miscminibuffer-prompt-end: Minibuffer Miscminibuffer-scroll-window: Minibuffer Miscminibuffer-setup-hook: Minibuffer Miscminibuffer-window: Minibuffer Miscminibuffer-window-active-p: Minibuffer Miscminor-mode-alist: Mode Line Variablesminor-mode-key-binding: Functions for Key Lookupminor-mode-map-alist: Active Keymapsminor-mode-overriding-map-alist: Active Keymapsminubuffer-prompt-width: Minibuffer Miscmisc-objects-consed: Memory Usagemod: Arithmetic Operationsmode-class property: Major Mode Conventionsmode-line (face name): Standard Facesmode-line prefix key: Key Sequence Inputmode-line-buffer-identification: Mode Line Variablesmode-line-format: Mode Line Datamode-line-frame-identification: Mode Line Variablesmode-line-inverse-video: Inverse Videomode-line-modified: Mode Line Variablesmode-line-mule-info: Mode Line Variablesmode-line-process: Mode Line Variablesmode-name: Mode Line Variablesmode-specific-map: Prefix Keysmodeline (face name): Standard Facesmodification-hooks (overlay property): Overlay Propertiesmodification-hooks (text property): Special Propertiesmodify-category-entry: Categoriesmodify-frame-parameters: Parameter Accessmodify-syntax-entry: Syntax Table Functionsmomentary-string-display: Temporary Displaysmouse-face (overlay property): Overlay Propertiesmouse-face (text property): Special Propertiesmouse-movement-p: Classifying Eventsmouse-pixel-position: Mouse Positionmouse-position: Mouse Positionmouse-position-function: Mouse Positionmouse-wheel event: Misc Eventsmove-marker: Moving Markersmove-overlay: Managing Overlaysmove-to-column: Columnsmove-to-left-margin: Marginsmove-to-window-line: Screen Linesmovemail: Subprocess Creationmule-keymap: Prefix Keysmultibyte-string-p: Text Representationsmultibyte-syntax-as-symbol: Parsing Expressionsmultiple-frames: Frame Titlesnarrow-to-page: Narrowingnarrow-to-region: Narrowingnatnump: Predicates on Numbersnbutlast: List Elementsnconc: Rearrangementnegative-argument: Prefix Command Argumentsnetwork-coding-system-alist: Default Coding Systemsnewline: Commands for Insertionnewline-and-indent: Mode-Specific Indentnext-char-property-change: Property Searchnext-frame: Finding All Framesnext-history-element: Minibuffer Miscnext-matching-history-element: Minibuffer Miscnext-overlay-change: Finding Overlaysnext-property-change: Property Searchnext-screen-context-lines: Textual Scrollingnext-single-char-property-change: Property Searchnext-single-property-change: Property Searchnext-window: Cyclic Window Orderingnil: Constant Variablesnil and lists: Cons Cellsnil in keymap: Key Lookupnil in lists: Cons Cell Typenil input stream: Input Streamsnil output stream: Output Streamsnil, uses of: nil and tnlistp: List-related Predicatesno-catch: Catch and Throwno-redraw-on-reenter: Refresh Screennonascii-insert-offset: Converting Representationsnonascii-translation-table: Converting Representationsnongregorian-diary-listing-hook: Hebrew/Islamic Entriesnongregorian-diary-marking-hook: Hebrew/Islamic Entriesnoninteractive: Batch Modenormal-auto-fill-function: Auto Fillingnormal-backup-enable-predicate: Making Backupsnormal-mode: Auto Major Modenot: Combining Conditionsnot-modified: Buffer Modificationnreverse: Rearrangementnth: List Elementsnthcdr: List Elementsnull: List-related Predicatesnum-input-keys: Key Sequence Inputnum-nonmacro-input-events: Key Sequence Inputnumber-of-diary-entries: Diary Customizingnumber-or-marker-p: Predicates on Markersnumber-to-string: String Conversionnumberp: Predicates on Numbersoccur-mode-map: Standard Keymapsone-window-p: Splitting Windowsonly-global-abbrevs: Defining Abbrevsopen-dribble-file: Recording Inputopen-network-stream: Networkopen-paren-in-column-0-is-defun-start: List Motionopen-termscript: Terminal Outputopen parenthesis character: Syntax Class Tableor: Combining Conditionsother-buffer: The Buffer Listother-holidays: Holiday Customizingother-window: Cyclic Window Orderingother-window-scroll-buffer: Textual Scrollingoverlay-arrow-position: Overlay Arrowoverlay-arrow-string: Overlay Arrowoverlay-buffer: Managing Overlaysoverlay-end: Managing Overlaysoverlay-get: Overlay Propertiesoverlay-put: Overlay Propertiesoverlay-start: Managing Overlaysoverlays-at: Finding Overlaysoverlays-in: Finding Overlaysoverriding-local-map: Active Keymapsoverriding-local-map-menu-flag: Active Keymapsoverriding-terminal-local-map: Active Keymapsoverwrite-mode: Commands for Insertionpage-delimiter: Standard Regexpspaired delimiter: Syntax Class Tableparagraph-separate: Standard Regexpsparagraph-start: Standard Regexpsparse-colon-path: System Environmentparse-partial-sexp: Parsing Expressionsparse-sexp-ignore-comments: Parsing Expressionsparse-sexp-lookup-properties: Syntax PropertiesPATH environment variable: Subprocess Creationpath-separator: System Environmentperform-replace: Search and Replaceplay-sound: Sound Outputplay-sound-file: Sound Outputplay-sound-functions: Sound Outputplist-get: Other Plistsplist-member: Other Plistsplist-put: Other Plistspoint-entered (text property): Special Propertiespoint-left (text property): Special Propertiespoint-marker: Creating Markerspoint-max: Pointpoint-max-marker: Creating Markerspoint-min: Pointpoint-min-marker: Creating Markerspop: List Elementspop-mark: The Markpop-to-buffer: Displaying Bufferspop-up-frame-alist: Choosing Windowpop-up-frame-function: Choosing Windowpop-up-frames: Choosing Windowpop-up-windows: Choosing Windowpos-visible-in-window-p: Window Startposition-bytes: Text Representationsposix-looking-at: POSIX Regexpsposix-search-backward: POSIX Regexpsposix-search-forward: POSIX Regexpsposix-string-match: POSIX Regexpsposn-col-row: Accessing Eventsposn-point: Accessing Eventsposn-timestamp: Accessing Eventsposn-window: Accessing Eventsposn-x-y: Accessing Eventspost-command-hook: Command Overviewpre-abbrev-expand-hook: Abbrev Expansionpre-command-hook: Command Overviewpreceding-char: Near Pointprefix-arg: Prefix Command Argumentsprefix-help-command: Help Functionsprefix-numeric-value: Prefix Command Argumentsprevious-char-property-change: Property Searchprevious-frame: Finding All Framesprevious-history-element: Minibuffer Miscprevious-matching-history-element: Minibuffer Miscprevious-overlay-change: Finding Overlaysprevious-property-change: Property Searchprevious-single-char-property-change: Property Searchprevious-single-property-change: Property Searchprevious-window: Cyclic Window Orderingprimitive-undo: Undoprin1: Output Functionsprin1-to-string: Output Functionsprinc: Output Functionsprint: Output Functionsprint-circle: Output Variablesprint-diary-entries: Diary Customizingprint-diary-entries-hook: Diary Customizingprint-escape-multibyte: Output Variablesprint-escape-newlines: Output Variablesprint-escape-nonascii: Output Variablesprint-gensym: Output Variablesprint-help-return-message: Help Functionsprint-length: Output Variablesprint-level: Output Variablespriority (overlay property): Overlay Propertiesprocess-buffer: Process Buffersprocess-coding-system: Process Informationprocess-coding-system-alist: Default Coding Systemsprocess-command: Process Informationprocess-connection-type: Asynchronous Processesprocess-contact: Process Informationprocess-environment: System Environmentprocess-exit-status: Process Informationprocess-filter: Filter Functionsprocess-id: Process Informationprocess-kill-without-query: Deleting Processesprocess-list: Process Informationprocess-mark: Process Buffersprocess-name: Process Informationprocess-running-child-p: Input to Processesprocess-send-eof: Input to Processesprocess-send-region: Input to Processesprocess-send-string: Input to Processesprocess-sentinel: Sentinelsprocess-status: Process Informationprocess-tty-name: Process Informationprocessp: Processesprog1: Sequencingprog2: Sequencingprogn: Sequencingpropertize: Changing Propertiesprovide: Named Featurespunctuation character: Syntax Class Tablepure-bytes-used: Pure Storagepurecopy: Pure Storagepurify-flag: Pure Storagepush: Building Listspush-mark: The Markput: Symbol Plistsput-image: Showing Imagesput-text-property: Changing Propertiesputhash: Hash Accessquery-replace-history: Minibuffer Historyquery-replace-map: Search and Replacequietly-read-abbrev-file: Abbrev Filesquit-flag: Quittingquit-process: Signals to Processesquote: Quotingquoted-insert suppression: Changing Key Bindingsraise-frame: Raising and Loweringrandom: Random Numbersrassoc: Association Listsrassq: Association Listsre-search-backward: Regexp Searchre-search-forward: Regexp Searchread: Input Functionsread-buffer: High-Level Completionread-buffer-function: High-Level Completionread-char: Reading One Eventread-char-exclusive: Reading One Eventread-coding-system: User-Chosen Coding Systemsread-command: High-Level Completionread-event: Reading One Eventread-expression-history: Minibuffer Historyread-file-name: Reading File Namesread-from-minibuffer: Text from Minibufferread-from-string: Input Functionsread-input-method-name: Input Methodsread-kbd-macro: Describing Charactersread-key-sequence: Key Sequence Inputread-key-sequence-vector: Key Sequence Inputread-minibuffer: Object from Minibufferread-no-blanks-input: Text from Minibufferread-non-nil-coding-system: User-Chosen Coding Systemsread-only (text property): Special Propertiesread-passwd: Reading a Passwordread-quoted-char: Quoted Character Inputread-quoted-char quitting: Quittingread-string: Text from Minibufferread-variable: High-Level Completionreal-last-command: Command Loop Inforecent-auto-save-p: Auto-Savingrecent-keys: Recording Inputrecenter: Textual Scrollingrecursion-depth: Recursive Editingrecursive-edit: Recursive Editingredirect-frame-focus: Input Focusredisplay-dont-pause: Forcing Redisplayredisplay-end-trigger-functions: Window Hooksredraw-display: Refresh Screenredraw-frame: Refresh Screenregexp-history: Minibuffer Historyregexp-opt: Regexp Functionsregexp-opt-depth: Regexp Functionsregexp-quote: Regexp Functionsregion (face name): Standard Facesregion-beginning: The Regionregion-end: The Regionregister-alist: Registersreindent-then-newline-and-indent: Mode-Specific Indentremhash: Hash Accessremove: Sets And Listsremove-from-invisibility-spec: Invisible Textremove-hook: Hooksremove-images: Showing Imagesremove-text-properties: Changing Propertiesremq: Building Listsrename-auto-save-file: Auto-Savingrename-buffer: Buffer Namesrename-file: Changing Filesreplace-buffer-in-windows: Displaying Buffersreplace-match: Replacing Matchrequire: Named Featuresrequire-final-newline: Saving Buffersno-redraw-on-reenter): Refresh Screenreverse: Building Listsrevert-buffer: Revertingrevert-buffer-function: Revertingrevert-buffer-insert-file-contents-function: Revertingrevert-without-query: Revertingright-margin-width: Display Marginsring-bell-function: Beepingrm: Changing Filesround: Numeric Conversionsrplaca: Modifying Listsrplacd: Modifying Listsrun-at-time: Timersrun-hook-with-args: Hooksrun-hook-with-args-until-failure: Hooksrun-hook-with-args-until-success: Hooksrun-hooks: Hooksrun-with-idle-timer: Timerssafe-length: List Elementssame-window-buffer-names: Choosing Windowsame-window-regexps: Choosing Windowsave-abbrevs: Abbrev Filessave-buffer: Saving Bufferssave-buffer-coding-system: Encoding and I/Osave-current-buffer: Current Buffersave-excursion: Excursionssave-match-data: Saving Match Datasave-restriction: Narrowingsave-selected-window: Selecting Windowssave-some-buffers: Saving Bufferssave-window-excursion: Window Configurationsscalable-fonts-allowed: Font Selectionscan-lists: Parsing Expressionsscan-sexps: Parsing Expressionsscreen-height: Size and Positionscreen-width: Size and Positionscroll-bar (face name): Standard Facesscroll-bar-event-ratio: Accessing Eventsscroll-bar-scale: Accessing Eventsscroll-conservatively: Textual Scrollingscroll-down: Textual Scrollingscroll-down-aggressively: Textual Scrollingscroll-left: Horizontal Scrollingscroll-margin: Textual Scrollingscroll-other-window: Textual Scrollingscroll-preserve-screen-position: Textual Scrollingscroll-right: Horizontal Scrollingscroll-step: Textual Scrollingscroll-up: Textual Scrollingscroll-up-aggressively: Textual Scrollingsearch-backward: String Searchsearch-failed: String Searchsearch-forward: String Searchsecondary-selection (face name): Standard Facesselect-frame: Input Focusselect-safe-coding-system: User-Chosen Coding Systemsselect-safe-coding-system-accept-default-p: User-Chosen Coding Systemsselect-window: Selecting Windowsselected-frame: Input Focusselected-window: Selecting Windowsselection-coding-system: Window System Selectionsselective-display: Selective Displayselective-display-ellipses: Selective Displayself-insert-and-exit: Minibuffer Miscself-insert-command: Commands for Insertionself-insert-command override: Changing Key Bindingsself-insert-command, minor modes: Keymaps and Minor Modessend-string-to-terminal: Terminal Outputsentence-end: Standard Regexpssentence-end-double-space: Fillingsequencep: Sequence Functionsset: Setting Variablesset-auto-mode: Auto Major Modeset-buffer: Current Bufferset-buffer-auto-saved: Auto-Savingset-buffer-major-mode: Auto Major Modeset-buffer-modified-p: Buffer Modificationset-buffer-multibyte: Selecting a Representationset-case-syntax: Case Tablesset-case-syntax-delims: Case Tablesset-case-syntax-pair: Case Tablesset-case-table: Case Tablesset-category-table: Categoriesset-char-table-default: Char-Tablesset-char-table-extra-slot: Char-Tablesset-char-table-parent: Char-Tablesset-char-table-range: Char-Tablesset-default: Default Valueset-default-file-modes: Changing Filesset-display-table-slot: Display Table Formatset-face-attribute: Attribute Functionsset-face-background: Attribute Functionsset-face-bold-p: Attribute Functionsset-face-font: Attribute Functionsset-face-foreground: Attribute Functionsset-face-italic-p: Attribute Functionsset-face-stipple: Attribute Functionsset-face-underline-p: Attribute Functionsset-file-modes: Changing Filesset-frame-configuration: Frame Configurationsset-frame-height: Size and Positionset-frame-position: Size and Positionset-frame-size: Size and Positionset-frame-width: Size and Positionset-input-method: Input Methodsset-input-mode: Input Modesset-keyboard-coding-system: Terminal I/O Encodingset-keymap-parent: Inheritance and Keymapsset-left-margin: Marginsset-mark: The Markset-marker: Moving Markersset-marker-insertion-type: Marker Insertion Typesset-match-data: Entire Match Dataset-mouse-pixel-position: Mouse Positionset-mouse-position: Mouse Positionset-process-buffer: Process Buffersset-process-coding-system: Process Informationset-process-filter: Filter Functionsset-process-sentinel: Sentinelsset-register: Registersset-right-margin: Marginsset-screen-height: Size and Positionset-screen-width: Size and Positionset-standard-case-table: Case Tablesset-syntax-table: Syntax Table Functionsset-terminal-coding-system: Terminal I/O Encodingset-text-properties: Changing Propertiesset-visited-file-modtime: Modification Timeset-visited-file-name: Buffer File Nameset-window-buffer: Buffers and Windowsset-window-configuration: Window Configurationsset-window-dedicated-p: Choosing Windowset-window-display-table: Active Display Tableset-window-hscroll: Horizontal Scrollingset-window-margins: Display Marginsset-window-point: Window Pointset-window-redisplay-end-trigger: Window Hooksset-window-start: Window Startset-window-vscroll: Vertical Scrollingsetcar: Setcarsetcdr: Setcdrsetenv: System Environmentsetplist: Symbol Plistssetprv: System Environmentsetq: Setting Variablessetq-default: Default Valuesetting-constant: Constant Variablesmode-line-format: Mode Line Datashell-command-history: Minibuffer Historyshell-command-to-string: Synchronous Processesshell-quote-argument: Shell Argumentsshow-help-function: Special Propertiesshow-trailing-whitespace: Standard Facesshrink-window: Resizing Windowsshrink-window-horizontally: Resizing Windowsshrink-window-if-larger-than-buffer: Resizing Windowssignal: Signaling Errorssignal-process: Signals to Processessimple-diary-display: Fancy Diary Displaysin: Math Functionssingle-key-description: Describing Characterssit-for: Waitingsite-run-file: Init Fileskip-chars-backward: Skipping Charactersskip-chars-forward: Skipping Charactersskip-syntax-backward: Motion and Syntaxskip-syntax-forward: Motion and Syntaxsleep-for: Waitingsmall-temporary-file-directory: Unique File NamesSnarf-documentation: Accessing Documentationsort: Rearrangementsort-columns: Sortingsort-diary-entries: Fancy Diary Displaysort-fields: Sortingsort-fold-case: Sortingsort-lines: Sortingsort-numeric-fields: Sortingsort-pages: Sortingsort-paragraphs: Sortingsort-regexp-fields: Sortingsort-subr: Sortingspecial: Major Mode Conventionsspecial-display-buffer-names: Choosing Windowspecial-display-frame-alist: Choosing Windowspecial-display-function: Choosing Windowspecial-display-popup-frame: Choosing Windowspecial-display-regexps: Choosing Windowspecial-event-map: Active Keymapssplit-char: Splitting Characterssplit-height-threshold: Choosing Windowsplit-line: Commands for Insertionsplit-string: Creating Stringssplit-window: Splitting Windowssplit-window-horizontally: Splitting Windowssplit-window-vertically: Splitting Windowssqrt: Math Functionsstandard-case-table: Case Tablesstandard-category-table: Categoriesstandard-display-table: Active Display Tablestandard-input: Input Functionsstandard-output: Output Variablesstandard-syntax-table: Standard Syntax Tablesstandard-translation-table-for-decode: Translation of Charactersstandard-translation-table-for-encode: Translation of Charactersstart-process: Asynchronous Processesstart-process-shell-command: Asynchronous Processesstop-process: Signals to Processesstore-match-data: Entire Match Datastore-substring: Modifying Stringsstring: Creating Stringsstring-as-multibyte: Selecting a Representationstring-as-unibyte: Selecting a Representationstring-chars-consed: Memory Usagestring-equal: Text Comparisonstring-lessp: Text Comparisonstring-make-multibyte: Converting Representationsstring-make-unibyte: Converting Representationsstring-match: Regexp Searchstring-to-char: String Conversionstring-to-int: String Conversionstring-to-number: String Conversionstring-to-syntax: Syntax Table Internalsstring-width: Widthstring<: Text Comparisonstring=: Text Comparisonstringp: Predicates for Stringsstrings-consed: Memory Usagestring quote: Syntax Class Tablesubr-arity: What Is a Functionsubrp: What Is a Functionsubst-char-in-region: Substitutionsubstitute-command-keys: Keys in Documentationsubstitute-in-file-name: File Name Expansionsubstitute-key-definition: Changing Key Bindingssubstring: Creating Stringssuppress-keymap: Changing Key Bindingsno-redraw-on-reenter): Refresh Screensuspend-emacs: Suspending Emacssuspend-hook: Suspending Emacssuspend-resume-hook: Suspending Emacsswitch-to-buffer: Displaying Buffersswitch-to-buffer-other-window: Displaying Bufferssxhash: Defining Hashsymbol-file: Unloadingsymbol-function: Function Cellssymbol-name: Creating Symbolssymbol-plist: Symbol Plistssymbol-value: Accessing Variablessymbolp: Symbolssymbols-consed: Memory Usagesymbol constituent: Syntax Class Tablesyntax-table: Syntax Table Functionssyntax-table (text property): Syntax Propertiessyntax-table-p: Syntax Basicssystem-configuration: System Environmentsystem-key-alist: Special Keysymssystem-messages-locale: Localessystem-name: System Environmentsystem-time-locale: Localessystem-type: System Environmentt: Constant Variablest and truth: nil and tt input stream: Input Streamst output stream: Output Streamstab-stop-list: Indent Tabstab-to-tab-stop: Indent Tabstab-width: Usual Displaytan: Math Functionstemacs: Building EmacsTEMP environment variable: Unique File Namestemp-buffer-setup-hook: Temporary Displaystemp-buffer-show-function: Temporary Displaystemp-buffer-show-hook: Temporary Displaystemporary-file-directory: Unique File NamesTERM environment variable: Terminal-Specificterm-file-prefix: Terminal-Specificterm-setup-hook: Terminal-Specificterminal-coding-system: Terminal I/O Encodingterpri: Output Functionstext-char-description: Describing Characterstext-mode-abbrev-table: Standard Abbrev Tablestext-mode-map: Standard Keymapstext-mode-syntax-table: Standard Syntax Tablestext-properties-at: Examining Propertiestext-property-any: Property Searchtext-property-default-nonsticky: Sticky Propertiestext-property-not-all: Property Searchthing-at-point: Buffer Contentsthis-command: Command Loop Infothis-command-keys: Command Loop Infothis-command-keys-vector: Command Loop Infothree-step-help: Help Functionsthrow: Catch and Throwthrow example: Recursive EditingTMP environment variable: Unique File NamesTMPDIR environment variable: Unique File Namestoday-invisible-calendar-hook: Calendar Customizingtoday-visible-calendar-hook: Calendar Customizingtoggle-read-only: Read Only Bufferstool-bar (face name): Standard Facestool-bar-add-item: Tool Bartool-bar-add-item-from-menu: Tool Bartool-bar-item-margin: Tool Bartool-bar-item-relief: Tool Bartool-bar-map: Tool Bartop-level: Recursive Editingtq-close: Transaction Queuestq-create: Transaction Queuestq-enqueue: Transaction Queuestrack-mouse: Mouse Trackingtrailing-whitespace (face name): Standard Facestransient-mark-mode: The Marktranslate-region: Substitutiontranspose-regions: Transpositiontruncate: Numeric Conversionstruncate-lines: Truncationtruncate-partial-width-windows: Truncationtruncate-string-to-width: Widthtry-completion: Basic Completiontty-color-alist: Text Terminal Colorstty-color-approximate: Text Terminal Colorstty-color-clear: Text Terminal Colorstty-color-define: Text Terminal Colorstty-color-translate: Text Terminal Colorstty-erase-char: System Environmenttype-of: Type Predicatesundefined: Functions for Key Lookupundefined in keymap: Key Lookupunderline (face name): Standard Facesundo-boundary: Undoundo-limit: Maintaining Undoundo-strong-limit: Maintaining Undounhandled-file-name-directory: Magic File Namesunintern: Creating Symbolsuniversal-argument: Prefix Command Argumentsunless: Conditionalsunload-feature: Unloadingunlock-buffer: File Locksunread-command-char: Event Input Miscunread-command-events: Event Input Miscunwind-protect: Cleanupsup-list: List Motionupcase: Case Conversionupcase-initials: Case Conversionupcase-region: Case Changesupcase-word: Case Changesupdate-directory-autoloads: Autoloadupdate-file-autoloads: Autoloaduse-global-map: Active Keymapsuse-hard-newlines: Fillinguse-local-map: Active Keymapsuser-full-name: User Identificationuser-init-file: Init Fileuser-login-name: User Identificationuser-mail-address: User Identificationuser-real-login-name: User Identificationuser-real-uid: User Identificationuser-uid: User Identificationuser-variable-p: Defining Variablesuser-variable-p example: High-Level Completionvalues: Evalvariable-documentation: Documentation Basicsvariable-interactive: Defining Variablesvariable-pitch (face name): Standard Facesvc-mode: Mode Line Variablesvc-prefix-map: Prefix Keysvconcat: Vector Functionsvector: Vector Functionsvector-cells-consed: Memory Usagevectorp: Vector Functionsverify-visited-file-modtime: Modification Timeversion-control: Numbered Backupsvertical-line prefix key: Key Sequence Inputvertical-motion: Screen Linesvertical-scroll-bar prefix key: Key Sequence Inputview-calendar-holidays-initially: Calendar Customizingview-diary-entries-initially: Calendar Customizingview-file: Visiting Functionsview-mode-map: Standard Keymapsview-register: Registersvisible-bell: Beepingvisible-frame-list: Finding All Framesvisited-file-modtime: Modification Timevoid-function: Function Cellsvoid-variable: Void Variableswaiting-for-user-input-p: Sentinelswalk-windows: Cyclic Window Orderingwhen: Conditionalswhere-is-internal: Scanning Keymapswhile: Iterationwhitespace character: Syntax Class Tablewholenump: Predicates on Numberswiden: Narrowingwindow (overlay property): Overlay Propertieswindow-at: Coordinates and Windowswindow-buffer: Buffers and Windowswindow-configuration-change-hook: Window Hookswindow-configuration-p: Window Configurationswindow-dedicated-p: Choosing Windowwindow-display-table: Active Display Tablewindow-edges: Size of Windowwindow-end: Window Startwindow-frame: Frames and 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Word Motionword constituent: Syntax Class Tablewrite-abbrev-file: Abbrev Fileswrite-char: Output Functionswrite-contents-hooks: Saving Bufferswrite-file: Saving Bufferswrite-file-hooks: Saving Bufferswrite-region: Writing to Fileswrite-region-annotate-functions: Saving Propertieswrong-number-of-arguments: Argument Listwrong-type-argument: Type Predicatesx-bitmap-file-path: Face Attributesx-close-connection: Multiple Displaysx-color-defined-p: Color Namesx-color-values: Color Namesx-defined-colors: Color Namesx-display-color-p: Display Feature Testingx-display-list: Multiple Displaysx-family-fonts: Font Lookupx-font-family-list: Font Lookupx-get-cut-buffer: Window System Selectionsx-get-resource: Resourcesx-get-selection: Window System Selectionsx-list-fonts: Font Lookupx-open-connection: Multiple Displaysx-parse-geometry: Size and Positionx-pointer-shape: Pointer Shapesx-popup-dialog: Dialog Boxesx-popup-menu: Pop-Up Menusx-resource-class: Resourcesx-select-enable-clipboard: Window System Selectionsx-sensitive-text-pointer-shape: Pointer Shapesx-server-vendor: Display Feature Testingx-server-version: Display Feature Testingx-set-cut-buffer: Window System Selectionsx-set-selection: Window System Selectionsy-or-n-p: Yes-or-No Queriesy-or-n-p-with-timeout: Yes-or-No Queriesyank: Yank Commandsyank-pop: Yank Commandsyes-or-no-p: Yes-or-No Querieszerop: Predicates on Numbersafter-make-frame-functions: Creating Framesassq-delete-all: Association Listsauto-raise-tool-bar-items: Tool Barauto-resize-tool-bar: Tool Barauto-save-list-file-prefix: Auto-Savingbackup-directory-alist: Making Backupsbase64-decode-region: Base 64base64-decode-string: Base 64base64-encode-region: Base 64base64-encode-string: Base 64beginning-of-defun-function: List Motionbuffer-has-markers-at: Information from Markersbyte-to-position: Text Representationscharset-bytes: Chars and Bytescharset-plist: Character Setsclear-face-cache: Font Selectionclear-image-cache: Image Cacheclear-this-command-keys: Command Loop Infoclrhash: Hash Accesscolor-defined-p: Color Namescolor-gray-p: Color Namescolor-supported-p: Color Namescolor-values: Color Namesconstrain-to-field: Fieldscopy-hash-table: Other Hashcreate-glyph: Glyphscreate-image: Defining Imagesdefault-header-line-format: Header Linesdefimage: Defining Imagesdefine-hash-table-test: Defining Hashdefine-minor-mode: Defining Minor Modesdefined-colors: Color Namesdelete-and-extract-region: Deletiondelete-field: Fieldsdelete-minibuffer-contents: Minibuffer Miscdescribe-current-display-table: Display Table Formatdescribe-display-table: Display Table Formatdisable-point-adjustment: Adjusting Pointdisplay-backing-store: Display Feature Testingdisplay-color-cells: Display Feature Testingdisplay-color-p: Display Feature Testingdisplay-graphic-p: Display Feature Testingdisplay-grayscale-p: Display Feature Testingdisplay-message-or-buffer: The Echo Areadisplay-mm-height: Display Feature Testingdisplay-mm-width: Display Feature Testingdisplay-mouse-p: Display Feature Testingdisplay-pixel-height: Display Feature Testingdisplay-pixel-width: Display Feature Testingdisplay-planes: Display Feature Testingdisplay-popup-menus-p: Display Feature Testingdisplay-save-under: Display Feature Testingdisplay-screens: Display Feature Testingdisplay-selections-p: Display Feature Testingdisplay-visual-class: Display Feature Testingdolist: Iterationdotimes: Iterationemacs-startup-hook: Init Fileend-of-defun-function: List Motionface-attribute: Attribute Functionsface-font-family-alternatives: Font Selectionface-font-registry-alternatives: Font Selectionface-font-selection-order: Font Selectionfield-beginning: Fieldsfield-end: Fieldsfield-string: Fieldsfield-string-no-properties: Fieldsfile-expand-wildcards: Contents of Directoriesfind-file-wildcards: Visiting Functionsfind-image: Defining Imagesfont-list-limit: Font Lookupfontification-functions: Auto Facesframe-parameter: Parameter Accessgethash: Hash Accessglobal-disable-point-adjustment: Adjusting Pointhash-table-count: Other Hashhash-table-p: Other Hashhash-table-rehash-size: Other Hashhash-table-rehash-threshold: Other Hashhash-table-size: Other Hashhash-table-test: Other Hashhash-table-weakness: Other Hashheader-line-format: Header Linesimage-cache-eviction-delay: Image Cacheimage-mask-p: Image Descriptorsimage-size: Showing Imagesindicate-empty-lines: Usual Displayinhibit-field-text-motion: Word Motioninhibit-modification-hooks: Change Hookskeywordp: Constant Variablesleft-margin-width: Display Marginsline-beginning-position: Text Linesline-end-position: Text Lineslocale-coding-system: Localesmake-backup-file-name-function: Making Backupsmake-category-table: Categoriesmake-hash-table: Creating Hashmake-temp-file: Unique File Namesmakehash: Creating Hashmapc: Mapping Functionsmaphash: Hash Accessminibuffer-contents: Minibuffer Miscminibuffer-contents-no-properties: Minibuffer Miscminibuffer-prompt-end: Minibuffer 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Defining Hashsystem-messages-locale: Localessystem-time-locale: Localestemp-buffer-setup-hook: Temporary Displaystext-property-default-nonsticky: Sticky Propertiestool-bar-add-item: Tool Bartool-bar-add-item-from-menu: Tool Bartool-bar-item-margin: Tool Bartool-bar-item-relief: Tool Bartool-bar-map: Tool Bartty-color-alist: Text Terminal Colorstty-color-approximate: Text Terminal Colorstty-color-clear: Text Terminal Colorstty-color-define: Text Terminal Colorstty-color-translate: Text Terminal Colorsuser-init-file: Init Filewindow-margins: Display Marginswindow-size-fixed: Resizing Windowswith-syntax-table: Syntax Table Functionswith-temp-message: The Echo Areax-family-fonts: Font Lookupx-font-family-list: Font Lookupdisplay Property
[1] There is no strictly equivalent way to add an element to
the end of a list. You can use (append listname (list
newelt)), which creates a whole new list by copying listname
and adding newelt to its end. Or you can use (nconc
listname (list newelt)), which modifies listname
by following all the cdrs and then replacing the terminating
nil. Compare this to adding an element to the beginning of a
list with cons, which neither copies nor modifies the list.
[2] This usage of “key” is not related to the term “key sequence”; it means a value used to look up an item in a table. In this case, the table is the alist, and the alist associations are the items.
[3] This definition of “environment” is specifically not intended to include all the data that can affect the result of a program.
[4] They may also be declared equivalently in cus-start.el.
[5] Button-down is the conservative antithesis of drag.
[6] It is required for menus which do not use a toolkit, e.g. under MS-DOS.
[7] An RFC, an acronym for Request for Comments, is a numbered Internet informational document describing a standard. RFCs are usually written by technical experts acting on their own initiative, and are traditionally written in a pragmatic, experience-driven manner.
[8] For an explanation of what is an RFC, see the footnote in Base 64.
[9] On other systems, Emacs uses a Lisp emulation of
ls; see Contents of Directories.
[10] The benefits of a Common Lisp-style package system are considered not to outweigh the costs.
[11] Consider that the package may be loaded arbitrarily by Custom for instance.