Two things: 1) syntax-classes can take parameters, so you can pass an argument to x that is a boolean, within-y?. You can't create a parameterization scope because this is all within the parsing code for syntax-parse. You could mutate a box or parameter with a ~do pattern and reset it after the patterns you want within that "scope," but c'mon. Don't do that.
(define-syntax-class (x within-y?) (pattern _ #:when within-y?)) (define-syntax-class y (pattern (~var dummy (x #t)))) [the use-case of nothing to the left of a : to indicate non-binding is something that should be extended to parameterized syntax-classes, probably.] 2) If you're communicating between macros and not syntax-classes, you want to use syntax-parameters. (require racket/stxparam) (define-syntax-parameter within-y? #f) (define-syntax-rule (y body) (syntax-parameterize ([within-y? #t]) body)) (define-syntax-class x (pattern _ #:when (syntax-parameter-value #'within-y?))) -Ian ----- Original Message ----- From: "Alexander D. Knauth" <[email protected]> To: "racket users list" <[email protected]> Sent: Friday, August 1, 2014 12:23:21 PM GMT -05:00 US/Canada Eastern Subject: [racket] is there any way to tell syntax-parse to parse a pattern within a parametization ? Is there any way to tell syntax-parse to parse a pattern within a parametization ? For example in something like this: (define within-y? (make-parameter #f)) (define-syntax-class x [pattern _ #:when (within-y?)]) (define-syntax-class y [pattern :x]) (define (parse stx) (syntax-parse stx [:y #t])) How do I tell it to parse the y syntax-class within a (parameterize ([within-y? #t]) …) form? ____________________ Racket Users list: http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
