[CM] need macro help!

[bil at ccrma.Stanford.EDU]

I think the "sexp" argument to map is just the
macro argument name 'sexp, so map can't figure
out what to do, and asks make-iterator to do
something (hence the make-iterator error).  I
would write the macro:

(define-macro (run-expr sexp)
   `(eval (map
	  (lambda(token)
             (if (and (symbol? token)
		     (eq? ((symbol->string token) 0) #\%))
		`(s4m-expr-inputs ,(string->number (substring (symbol->string token) 
1)))
		token))
	  ,sexp))

so (s4m-run-expr "(+ %1 %2 %3)") returns 66.

If you omit the eval (to see what code is being generated),

   (s4m-run-expr "(+ %1 %2 %3)")

returns

   (+ (s4m-expr-inputs 1) (s4m-expr-inputs 2) (s4m-expr-inputs 3))