From: "Marijn Schouten (hkBst)" <hkbst@gentoo.org>
To: Matthew Flatt <mflatt@cs.utah.edu>, Eli Barzilay <eli@barzilay.org>
Cc: "dev@racket-lang.org" <dev@racket-lang.org>,
"Ludovic Courtès" <ludo@gnu.org>,
guile-devel@gnu.org
Subject: Re: [racket-dev] Enhancement to the syntax system?
Date: Sat, 03 May 2014 23:29:21 +0200 [thread overview]
Message-ID: <53655FB1.5060702@gentoo.org> (raw)
In-Reply-To: <20120710150315.B7B27650059@mail-svr1.cs.utah.edu>
On 07/10/2012 05:03 PM, Matthew Flatt wrote:
> 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)
IIUC then you're saying that also all the following (fx #'x) and (fy
#'x) are equivalent to #`(let ((x 0)) x), but if you run this code then
you will get a 0 result only for (myy), contrary to what I would expect
based on the above explanation.
#lang racket
(define-for-syntax (fx x) #`(let ((x 0)) #,x))
(define-for-syntax (fy y) #`(let ((x 0)) #,y))
(define-syntax (mxx x)
(syntax-case x () ((_) #`(let ((x 99)) #,(fx #'x)))))
(define-syntax (mxy x)
(syntax-case x () ((_) #`(let ((x 99)) #,(fy #'x)))))
(define-syntax (myx y)
(syntax-case y () ((_) #`(let ((x 99)) #,(fx #'x)))))
(define-syntax (myy y)
(syntax-case y () ((_) #`(let ((x 99)) #,(fy #'x)))))
(mxx)
(mxy)
(myx)
(myy)
==>
99
99
99
0
Marijn
next prev parent reply other threads:[~2014-05-03 21:29 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
2012-07-10 15:26 ` [racket-dev] " 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) [this message]
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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