[racket-dev] can a syntax-class "inherit" attributes?

You'd have to ask Ryan to be sure, but I think they're pretty stable.  I've
been using them for some time.

Carl Eastlund


On Fri, Aug 23, 2013 at 12:53 PM, Stephen Chang <stchang at ccs.neu.edu> wrote:

> Ah, thanks. That's exactly what I wanted.
>
> How stable are these features? Shall I add them to the docs?
>
> On Fri, Aug 23, 2013 at 12:54 AM, Carl Eastlund <cce at ccs.neu.edu> wrote:
> > Here's how you want to define AorB:
> >
> > (define-syntax-class AorB #:auto-nested-attributes
> >   (pattern :A)
> >   (pattern :B))
> >
> > There's two things going on here, both of which I believe are
> undocumented,
> > sadly.
> >
> > One is #:auto-nested-attributes, an option that tells AorB that anything
> > bound as an attribute by nested sub-patterns in its clauses should
> > automatically become an attribute of AorB.
> >
> > The other is that empty identifier does not add "." to its attribute
> names.
> > When you bind a with the attribute X, you get A.X, and when you bind b,
> you
> > get b.X, but when you bind the empty identifier, you just get X.
> >
> > So now you just have X bound in both clauses, and that's automatically
> made
> > an attribute of AorB, and it all works like you want.
> >
> > Carl Eastlund
> >
> >
> > On Fri, Aug 23, 2013 at 12:22 AM, Stephen Chang <stchang at ccs.neu.edu>
> wrote:
> >>
> >> Is there a way for a syntax-class to automatically inherit attributes?
> >>
> >> For example, the third class below combines the first two. Is there a
> >> way to automatically get the attributes from the first two classes in
> >> the third one (ie, I want to drop the "#:attr X #'a.X" part in the
> >> third class)?
> >>
> >> #lang racket
> >> (require syntax/parse)
> >>
> >> (define-syntax-class A (pattern (a b) #:attr X #'b))
> >> (define-syntax-class B (pattern (a b c) #:attr X #'c))
> >> (define-syntax-class AorB
> >>   (pattern a:A #:attr X #'a.X)
> >>   (pattern b:B #:attr X #'b.X))
> >>
> >> (syntax-parse #'(list 1) [ab:AorB (attribute ab.X)])
> >> _________________________
> >>   Racket Developers list:
> >>   http://lists.racket-lang.org/dev
> >>
> >
>
>
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