From: Matthew Flatt <mflatt-sDh8Nw2yj/+Vc3sceRu5cw@public.gmane.org>
To: Eli Barzilay <eli-oSK4jVRJLyZg9hUCZPvPmw@public.gmane.org>
Cc: "dev-GvBox1K3Ixw1Q5oZIJT9Xw@public.gmane.org"
<dev-GvBox1K3Ixw1Q5oZIJT9Xw@public.gmane.org>,
"Ludovic Courtès" <ludo-mXXj517/zsQ@public.gmane.org>,
guile-devel-mXXj517/zsQ@public.gmane.org
Subject: Re: Enhancement to the syntax system?
Date: Tue, 10 Jul 2012 09:03:14 -0600 [thread overview]
Message-ID: <20120710150315.B7B27650059@mail-svr1.cs.utah.edu> (raw)
In-Reply-To: <20476.16781.257276.194149-a5nvgYPMCZcx/1z6v04GWfZ8FUJU4vz8@public.gmane.org>
At Tue, 10 Jul 2012 10:51:57 -0400, Eli Barzilay wrote:
> 20 minutes ago, Marijn wrote:
> >
> > It seems to me that both these results cannot be correct
> > simultaneously, but I'll await the experts' opinion on that.
>
> This does look weird:
>
> #lang racket
> (define-for-syntax (f stx) #`(let ([x 1]) #,stx))
> (define-syntax (m stx)
> (with-syntax ([zz (f #'x)]) #`(let ([x 2]) zz)))
> (m)
>
> evaluates to 1, but if I change the first two "stx" names into "x"
> *or* if I change the argument name for the macro to "x", then it
> returns 2.
It's natural --- but not correct --- to think that #` is responsible
for hygiene, in which case `(f #'x)' should keep the given `x' separate
from the `let'-bound `x' in the result.
Instead, hygiene is the responsibility of macro invocation, and
#`(let ([x 1]) #,#'x)
is simply the same as
#`(let ([x 1]) x)
and so
(f #'x)
above is equivalent to
#`(let ([x 1]) x)
If you change the example to
#lang racket
(begin-for-syntax
(define-syntax-rule (f body)
#`(let ([x 1]) body)))
(define-syntax (m stx)
(with-syntax ([zz (f x)]) #`(let ([x 2]) zz)))
(m)
so that `f' is used as a macro instead of a function, then you get 2,
since the macro-expansion of `(f x)' keeps the `x's separate.
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next prev parent reply other threads:[~2012-07-10 15:03 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-30 15:22 Enhancement to the syntax system? Stefan Israelsson Tampe
2012-07-02 19:28 ` Ludovic Courtès
2012-07-02 20:43 ` Stefan Israelsson Tampe
2012-07-02 22:41 ` Ludovic Courtès
2012-07-03 14:37 ` Stefan Israelsson Tampe
2012-07-03 21:33 ` Ludovic Courtès
2012-07-03 21:52 ` Stefan Israelsson Tampe
2012-07-04 7:47 ` Marijn
2012-07-04 8:04 ` Stefan Israelsson Tampe
2012-07-09 15:52 ` Ludovic Courtès
2012-07-09 17:40 ` Stefan Israelsson Tampe
2012-07-10 8:24 ` Ludovic Courtès
2012-07-10 13:35 ` Stefan Israelsson Tampe
2012-07-10 14:34 ` Marijn
2012-07-10 14:51 ` [racket-dev] " Eli Barzilay
[not found] ` <20476.16781.257276.194149-a5nvgYPMCZcx/1z6v04GWfZ8FUJU4vz8@public.gmane.org>
2012-07-10 15:03 ` Matthew Flatt [this message]
2012-07-10 15:26 ` Ludovic Courtès
2012-07-10 15:44 ` Stefan Israelsson Tampe
2012-07-10 17:47 ` Stefan Israelsson Tampe
2012-07-10 16:48 ` Eli Barzilay
2014-05-03 21:29 ` Marijn Schouten (hkBst)
2012-07-10 15:44 ` Ryan Culpepper
2012-07-10 15:22 ` Ludovic Courtès
2012-07-10 7:36 ` Stefan Israelsson Tampe
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