Node:Unique Values, Previous:Boolean Data, Up:Immediate Datatypes
The immediate values that are neither small integers, characters, nor booleans are all unique values -- that is, datatypes with only one instance.
| SCM SCM_EOL | Macro |
The Scheme empty list object, or "End Of List" object, usually written
in Scheme as '().
|
| SCM SCM_EOF_VAL | Macro |
| The Scheme end-of-file value. It has no standard written representation, for obvious reasons. |
| SCM SCM_UNSPECIFIED | Macro |
|
The value returned by expressions which the Scheme standard says return
an "unspecified" value.
This is sort of a weirdly literal way to take things, but the standard read-eval-print loop prints nothing when the expression returns this value, so it's not a bad idea to return this when you can't think of anything else helpful. |
| SCM SCM_UNDEFINED | Macro |
|
The "undefined" value. Its most important property is that is not
equal to any valid Scheme value. This is put to various internal uses
by C code interacting with Guile.
For example, when you write a C function that is callable from Scheme
and which takes optional arguments, the interpreter passes
We also use this to mark unbound variables. |
| int SCM_UNBNDP (SCM x) | Macro |
Return true if x is SCM_UNDEFINED. Apply this to a
symbol's value to see if it has a binding as a global variable.
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