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

From: Eric Dobson (eric.n.dobson at gmail.com)
Date: Sun May 5 16:21:16 EDT 2013

Version 1 was what I meant by not duplicating work, and version 2
seems much too complicated.

It looks like syntax/parse/experimental/eh, does what I need.

On Sun, May 5, 2013 at 1:11 PM, J. Ian Johnson <ianj at ccs.neu.edu> wrote:
> 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" <eric.n.dobson at gmail.com>
> To: users at racket-lang.org
> 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 ...)
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