The `syntax-local-introduce` solution breaks when the macro is used from a
different module.
The datum->syntax solution may or may not have the behavior you are looking
for:
#lang racket
(module a racket
(require (for-syntax syntax/parse))
(require (for-syntax racket/syntax))
(define x 'a)
(define-syntax (my-macro stx)
(syntax-parse stx
[(_ x:id)
#:with a #'a
#:with y (datum->syntax #'a (syntax-e #'x))
#`(lambda (a b) y)]))
(provide my-macro))
(require 'a)
; These work
((my-macro a) 1 2) ; => 1
((my-macro b) 1 2) ; => 2
; Is this what you want?
(define x 'b)
((my-macro x) 1 2) ; => 'a
Notice that references are resolved in the complete environment of the
macro definition site, and not only to names bound in the macro-generated
template.
An alternative approach would be to have the macro unhygienicially
introduce the *bindings* a and b. The effect is different:
#lang racket
(module a racket
(require (for-syntax syntax/parse))
(require (for-syntax racket/syntax))
(define-syntax (my-macro stx)
(syntax-parse stx
[(_ x:id)
#:with a (datum->syntax this-syntax 'a)
#:with b (datum->syntax this-syntax 'b)
#`(lambda (a b) x)]))
(provide my-macro))
(require 'a)
; These work
((my-macro a) 1 2) ; => 1
((my-macro b) 1 2) ; => 2
; Is this what you want?
(define x 'b)
((my-macro x) 1 2) ; => 'b
On Saturday, February 23, 2019 at 8:22:57 AM UTC-5, Stefano Lande wrote:
>
> Thanks to both of you, it is exactly what I was trying to do.
>
> Stefano
>
> Il giorno ven 22 feb 2019 alle ore 18:37 Matthias Felleisen <
> matt...@felleisen.org <javascript:>> ha scritto:
>
>>
>> And that’s better of course because you pick up the lexical scope, which
>>
>> (let ([x 4]) [(my-macro x) 1 2])
>>
>> shows.
>>
>>
>>
>> > On Feb 22, 2019, at 1:26 PM, Sam Caldwell <sa...@ccs.neu.edu
>> <javascript:>> wrote:
>> >
>> > You can also do this with syntax-local-introduce to remove x's use-site
>> scope*:
>> >
>> > #lang racket
>> >
>> > (require (for-syntax syntax/parse))
>> >
>> > (define-syntax (my-macro stx)
>> > (syntax-parse stx
>> > [(_ x:id)
>> > #:with x- (syntax-local-introduce #'x)
>> > #'(lambda (a b) x-)]))
>> >
>> > ((my-macro a) 1 2)
>> > ;; 1
>> >
>> > ((my-macro b) 1 2)
>> > ;; 2
>> >
>> > (define x 3)
>> > ((my-macro x) 1 2)
>> > ;; 3
>> >
>> >
>> >
>> > -Sam
>> >
>> > * well, I think that's what's going on.
>> >
>> > On Fri, Feb 22, 2019 at 1:21 PM Matthias Felleisen <
>> matt...@felleisen.org <javascript:>> wrote:
>> >
>> >
>> > > On Feb 22, 2019, at 1:08 PM, Stefano Lande <land...@gmail.com
>> <javascript:>> wrote:
>> > >
>> > > Dear all,
>> > >
>> > > first of all, I might being misusing the terminology. Sorry about it.
>> > >
>> > > I would like to write a macro that gets an identifier and return its
>> value in the new lexical scope created by the macro.
>> > > For example:
>> > >
>> > > > (define-syntax (my-macro stx)
>> > > (syntax-parse stx
>> > > [(_ x:id) #'(lambda (a b) x) ]))
>> > >
>> > >
>> > > > ((my-macro a) 1 2)
>> > > 1
>> > >
>> > > >((my-macro b) 1 2)
>> > > 2
>> > >
>> > >
>> > >
>> > > my-macro as above of course would not work. Is possible to receive an
>> identifier, strip the lexical context, and evaluate it in the context of
>> (lambda (a b) body) ?
>> >
>> >
>> > Here is one way to get your macro:
>> >
>> > #lang racket
>> >
>> > (require (for-syntax syntax/parse))
>> > (require (for-syntax racket/syntax))
>> >
>> > (define-syntax (my-macro stx)
>> > (syntax-parse stx
>> > [(_ x:id)
>> > #:with a #'a
>> > #:with y (datum->syntax #'a (syntax-e #'x))
>> > #`(lambda (a b) y)]))
>> >
>> > [(my-macro a) 1 2]
>> > [(my-macro b) 1 2]
>> > (define x 3)
>> > [(my-macro x) 1 2]
>> >
>> > --
>> > You received this message because you are subscribed to the Google
>> Groups "Racket Users" group.
>> > To unsubscribe from this group and stop receiving emails from it, send
>> an email to racket-users...@googlegroups.com <javascript:>.
>> > For more options, visit https://groups.google.com/d/optout.
>>
>>
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