How to set default or optional parameters in scheme?

user_896112 0
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I'm trying to figure out how to how to set default or optional parameters in Scheme.

I've tried (define (func a #!optional b) (+ a b)) but I can't find of a way to check if b is a default parameter, because simply calling (func 1 2) will give the error:

Error: +: number required, but got #("halt") [func, +]

I've also tried (define (func a [b 0]) (+ a b)) but I get the following error:

Error: execute: unbound symbol: "b" [func]

If it helps I'm using BiwaScheme as used in repl.it

scheme lisp
3 Answers

MIT/GNU Scheme doc for this purpose.

(define (f a #!optional b)
  (+ a
     (if (default-object? b)
         0
         b)))

; test
(f 1) ; 1
(f 1 2) ; 3
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