[racket-dev] Enhancement to the syntax system?

I realize this is a very old thread, but the behavior of Racket has not
changed since.

On 03-05-14 23:29, Marijn Schouten (hkBst) wrote:
> 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
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