[racket] syntax-parse and matching ordered optional keyworded expressions

From: Eric Dobson (eric.n.dobson at gmail.com)
Date: Sun May 5 15:58:31 EDT 2013

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

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:
 (~optional guard:guard-form)
 (~optional mutable:mutable-form)
 property:struct-property-form) ...
#'(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 ...)
#'(form.contracted ...)

Posted on the users mailing list.