First note there is more than one code/macro expander for Gambit: Gambit's default, the one with Black Hole, and the syntax-case library file, for instance.

2012/8/26 Bob McIsaac <bobmc_net@rogers.com>
Hi:

3 questions...

I'm looking for a "when" macro and tried one patterned on "unless". It behaves like "when-not". How do I write a proper "when" macro?

(define-syntax when-not
  (syntax-rules ()
    ((when-not test body ...)
     (if test #t (begin body ...)))))

(define (test-when n) 
  (when-not (not (< n 50))
      (println "line1 " n)
      (println "line2 " n)
      (println "line3 " n)))
(test-when 0) (test-when 3) (test-when 55)
;-------------------------------------------

I'm not clear about what you are trying to achieve here.
 
Re "define-syntax" the Gambit-C manual says .."Note that this implementation of syntax-case does not support special forms that are specific to Gambit." What are the implications of this statement? Is there a preferred model for writing Gambit-C macros?

No support for #!rest #!optional #!key would be a good start. Not clear atm about more.
 
;------------------------------------------------------------

Some code has a "##" prefix like..
(##define-macro (err form)
  `(let ()
     (##declare (safe) (generic))
     (err-form (lambda () ,form))))

Why is that?

Generally in Gambit ##-prefixes on Gambit-provided procedures is to say it's the non-typechecked variant.

As for Gambit-provided syntactical forms (##define-macro ##lambda etc.) I believe they're equivalent with the non-prefixed variant.

Brgds
 
=bob=


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