Question

I have a Scheme macro and a long list, and I’d like to map the macro across the list, just as if it were a function. How can I do that using R5RS?

The macro accepts several arguments:

(mac a b c d)

The list has

(define my-list ((a1 b1 c1 d1)
                 (a2 b2 c2 d2)
                 ...
                 (an bn cn dn)))

And I’d like to have this:

(begin
   (mac a1 b1 c1 d2)
   (mac a2 b2 c2 d2)
   ...
   (mac an bn cn dn))

(By the way, as you can see I’d like to splice the list of arguments too)

Answer 1

Expanding on z5h’s answer of using eval, the methods below show how a map-macro macro can be written if interaction-environment in implemented in the version of R5RS in use:

(define test-list '((1 2 3 4)
                    (5 6 7 8)))

;Or if your version of scheme implments interaction-environment then:
(define-syntax trade
  (syntax-rules ()
    ((_ a b c d) (display (list b a d c)))))

;!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
;Careful this is not really mapping. More like combined map and apply.
;!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
(define-syntax map-macro
  (syntax-rules ()
    ((_ mac ls) (let ((mac-list (map (lambda (lst) (cons 'trade lst)) ls)))
                          (eval 
                           `(begin
                              ,@mac-list)
                           (interaction-environment))))
                        ))

(map-macro trade test-list)
;outputs: (2 1 4 3)(6 5 8 7)

So that last map-macro call evaluates the following:

What ends up getting evaluated from (map-macro trade test-list) is:

(begin
  (trade 1 2 3 4)
  (trade 5 6 7 8))

Which is not quite a map, but I believe it does answers your question.