Node:let-optional Reference, Next:let-keywords Reference, Up:Optional Arguments
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* (see Local Bindings).
| let-optional rest-arg (binding ...) expr ... | library syntax |
| let-optional* rest-arg (binding ...) expr ... | library syntax |
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. |