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Re: Enhancement to the syntax system?

From: Stefan Israelsson Tampe
Subject: Re: Enhancement to the syntax system?
Date: Wed, 4 Jul 2012 10:04:15 +0200

Funny,  for guile I get,
scheme@(guile-user)> (define (f x) #`(let ((x 1)) #,x))
scheme@(guile-user)> (define-syntax m (lambda (x) (syntax-case x () ((_) #`(let ((x 2)) #,(f #'x))))))
scheme@(guile-user)> (m)
$1 = 1

I ported the racket matcher to guile and worked in that environment, so this illustrate the problem.
In racket the same idea will error out as you say (I did not find anything wrong with your example).
I do prefer the racket behavior of bailing out because it can help detecting the bug in stead of silently
behave against the intention for newbies. My original code where this issue comes from is located in
compat/racket/match/match.scm in the syntax-parse repo at

This is the racket matcher implemented using syntax-parse!

These bugs should have been corrected though in that code!


On Wed, Jul 4, 2012 at 9:47 AM, Marijn <address@hidden> wrote:
Hash: SHA1

Hi Stefan,

On 03-07-12 23:52, Stefan Israelsson Tampe wrote:
> You do not need gensyms if you try to mimic or implement my
> suggested #. . On the other hand when if you do this
> (define (f stx) #`(let ((x 1)) #,stx))
> and use this with
> #`(let ((x 2)) #,(f #'x))
> the resulting expanded code would produce 1 which is not what you
> want.

I tried it in Racket:

(define-for-syntax (f stx) #`(let ((x 1)) #,stx))

(define-syntax (m stx)
  (syntax-case stx ()
    ((_) #`(let ((x 2)) #,(f #'x))) ))


but I get error messages which I don't know what to do about. Do you
have running examples of code not producing the result you want?

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