Guile Reference Manual
23.2 Optional Arguments
Scheme procedures, as defined in R5RS, can either handle a fixed number
of actual arguments, or a fixed number of actual arguments followed by
arbitrarily many additional arguments. Writing procedures of variable
arity can be useful, but unfortunately, the syntactic means for handling
argument lists of varying length is a bit inconvenient. It is possible
to give names to the fixed number of argument, but the remaining
(optional) arguments can be only referenced as a list of values
(see section 23.1 Lambda: Basic Procedure Creation).
Guile comes with the module (ice-9 optargs), which makes using
optional arguments much more convenient. In addition, this module
provides syntax for handling keywords in argument lists
(see section 21.7 Keywords).
Before using any of the procedures or macros defined in this section,
you have to load the module (ice-9 optargs) with the statement:
| | (use-modules (ice-9 optargs))
|
