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 <c...@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 <stch...@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 >> > _________________________ Racket Developers list: http://lists.racket-lang.org/dev
