# [racket-dev] Enhancement to the syntax system?

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