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33.2.2 Common Feature Symbols

In general, a particular feature may be available for one of two reasons. Either because the Guile library was configured and compiled with that feature enabled -- i.e. the feature is built into the library on your system. Or because some C or Scheme code that was dynamically loaded by Guile has added that feature to the list.

In the first category, here are the features that the current version of Guile may define (depending on how it is built), and what they mean.

array

Indicates support for arrays (see Arrays).

array-for-each

Indicates availability of array-for-each and other array mapping procedures (see Array Mapping).

char-ready?

Indicates that the char-ready? function is available (see Reading).

complex

Indicates support for complex numbers.

current-time

Indicates availability of time-related functions: times, get-internal-run-time and so on (see Time).

debug-extensions

Indicates that the debugging evaluator is available, together with the options for controlling it.

delay

Indicates support for promises (see Delayed Evaluation).

EIDs

Indicates that the geteuid and getegid really return effective user and group IDs (see Processes).

inexact

Indicates support for inexact numbers.

i/o-extensions

Indicates availability of the following extended I/O procedures: ftell, redirect-port, dup->fdes, dup2, fileno, isatty?, fdopen, primitive-move->fdes and fdes->ports (see Ports and File Descriptors).

net-db

Indicates availability of network database functions: scm_gethost, scm_getnet, scm_getproto, scm_getserv, scm_sethost, scm_setnet, scm_setproto, scm_setserv, and their `byXXX' variants (see Network Databases).

posix

Indicates support for POSIX functions: pipe, getgroups, kill, execl and so on (see POSIX).

random

Indicates availability of random number generation functions: random, copy-random-state, random-uniform and so on (see Random).

reckless

Indicates that Guile was built with important checks omitted -- you should never see this!

regex

Indicates support for POSIX regular expressions using make-regexp, regexp-exec and friends (see Regexp Functions).

socket

Indicates availability of socket-related functions: socket, bind, connect and so on (see Network Sockets and Communication).

sort

Indicates availability of sorting and merging functions (see Sorting).

system

Indicates that the system function is available (see Processes).

threads

Indicates support for multithreading (see Threads).

values

Indicates support for multiple return values using values and call-with-values (see Multiple Values).

Available features in the second category depend, by definition, on what additional code your Guile process has loaded in. The following table lists features that you might encounter for this reason.

defmacro

Indicates that the defmacro macro is available (see Macros).

describe

Indicates that the (oop goops describe) module has been loaded, which provides a procedure for describing the contents of GOOPS instances.

readline

Indicates that Guile has loaded in Readline support, for command line editing (see Readline Support).

record

Indicates support for record definition using make-record-type and friends (see Records).

Although these tables may seem exhaustive, it is probably unwise in practice to rely on them, as the correspondences between feature symbols and available procedures/behaviour are not strictly defined. If you are writing code that needs to check for the existence of some procedure, it is probably safer to do so directly using the defined? procedure than to test for the corresponding feature using feature?.