[racket] Macro Help

From: Helmut Rohrbacher (helmut.rohrbacher at gmail.com)
Date: Sun Feb 26 19:18:37 EST 2012

I'm trying to write a macro provide a new way to define functions so that:

(define fold-left
   _ i '() -> i
   f i (cons x xs) -> (fold-left f (f i x) xs)))

Would be valid syntax that would expand to:

(define fold-left
    [(list _ i '()) i]
    [(list f i (cons x xs)) (fold-left f (f i x) xs)]))

So far I have been able to get there half-way by wrapping each *args ...* ->
*body* pattern in parens, which makes the above declaration look like this:

(define fold-left
   [_ i '() -> i]
   [f i (cons x xs) -> (fold-left f (f i x) xs)]))

By using this macro:

(define-syntax function
  (syntax-rules (->)
    [(_ (args ... -> body) ...)
       [(list args ...) body]

What macro voodoo do I need to harness in order to be able to implement the
first definition syntax where the *args ... -> body* segments need not be
wrapped in parens?

BTW, first time poster, so go easy on me :)

Thanks a bunch!
-- Helmut
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