C[omp]ute

From: "andrew cooke" <andrew@...>

Date: Sun, 19 Aug 2007 08:57:04 -0400 (CLT)

I may be misunderstanding hygienic macros here, but as far as I can tell I
am getting variable capture.

(define-syntax bad
  (syntax-rules ()
    ((_ (arg1 ...) (arg2 ...))
     (receive (a b c) (values arg1 ...)
       (newline)
       (write (list arg2 ...))))))

(receive (a b c) (values 1 2 3) (bad (7 8 9) (a b c)))

This displays (7 8 9) when arg2 should be (1 2 3) (the value of a b c in
the calling code, not the value in "bad").

For comparison, similar code with "let" instead of "receive" works as
expected:

(define-syntax bad2
  (syntax-rules ()
    ((_ arg1 arg2)
     (let ((a arg1))
         (newline)
         (write arg2)))))

(let ((a 1)) (bad2 7 a))

This displays "1".

Gambit Version 4.0 beta 22, on Suse linux 10.2, amd64.

Andrew