One way is to have your ~or form in an ~and with a catch-all where you can observe the ordering. That is, (~and (~seq forms ...) (~seq (~or (~optional (~seq #:kw0 kw0)) ...others...) ...)) Then walk through (forms ...) when you're outputting your changed keyword arguments to determine which to output. Say, build a table of keyword to output for that keyword. You could also trust that syntax-parse will parse your dotted ~or in order and have ~do forms that populate a data structure via mutation and bump up a counter each time.
-Ian ----- Original Message ----- From: "Eric Dobson" <[email protected]> To: [email protected] Sent: Sunday, May 5, 2013 3:58:31 PM GMT -05:00 US/Canada Eastern Subject: [racket] syntax-parse and matching ordered optional keyworded expressions I'm trying to improve the struct: form in TR, and one of the things I need to do is match a sequence of keyworded expressions, add annotations on the expressions, and then put them back into the same order. I can either do a large ~or clause and have optional constraints on each clause, but If I do this then each kind of clause needs a different name and then putting them back in the same order is difficult. If I make a syntax class with each kind of clause then I don't know how to enforce the at most one constraint. Is there a way to do this with out duplicating the parsing work? Method 1: (~or (~optional guard:guard-form) (~optional mutable:mutable-form) property:struct-property-form) ... and #'(guard.contracted mutable.contracted property.contracted ...)) Method 2: (define-splicing-syntax-class any-form (pattern :guard-form) (pattern :mutable-form) (pattern :struct-property-form)) (form:any-form ...) and #'(form.contracted ...) ____________________ Racket Users list: http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
