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(guile.info.gz) Optional Arguments
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23.2.1 let-optional Reference
-----------------------------
The syntax `let-optional' and `let-optional*' are for destructuring
rest argument lists and giving names to the various list elements.
`let-optional' binds all variables simultaneously, while
`let-optional*' binds them sequentially, consistent with `let' and
`let*' ( Local Bindings).
-- library syntax: let-optional rest-arg (binding ...) expr ...
-- library syntax: let-optional* rest-arg (binding ...) expr ...
These two macros give you an optional argument interface that is
very "Schemey" and introduces no fancy syntax. They are compatible
with the scsh macros of the same name, but are slightly extended.
Each of BINDING may be of one of the forms VAR or `(VAR
DEFAULT-VALUE)'. REST-ARG should be the rest-argument of the
procedures these are used from. The items in REST-ARG are
sequentially bound to the variable names are given. When REST-ARG
runs out, the remaining vars are bound either to the default
values or `#f' if no default value was specified. REST-ARG remains
bound to whatever may have been left of REST-ARG.
After binding the variables, the expressions EXPR ... are
evaluated in order.
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(guile.info.gz) Optional Arguments
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