On Thu, Apr 16, 2015 at 7:32 AM, Alexander D. Knauth <alexan...@knauth.org> wrote: > > >>> On Apr 15, 2015, at 2:29 PM, Jon Zeppieri <zeppi...@gmail.com> wrote: >>> >>>> I'm trying to provide a struct, the struct type of which uses >>>> prop:procedure and prop:match-expander, and I'd like the procedure to >>>> have a contract. > > >>> On Apr 15, 2015, at 10:12 PM, Jon Zeppieri <zeppi...@gmail.com> wrote: >>> >>>> It's an instance of a struct. Here's the background: I have a struct >>>> type, created with `struct`, which has its own constructor and match >>>> expander. However, I don't want to use that constructor or match >>>> expander as part of the public interface. (The struct contains some >>>> fields that should be treated as private.) Now, the only way I know to >>>> provide a single identifier that can act as both a struct constructor >>>> and a match expander is to use a struct. So, in this case, I need to >>>> use a *different* struct type, an instance of which can be used, on >>>> one hand, as a procedure to construct an instance of the original >>>> struct type, and on the other, as a match expander (also for the >>>> original struct type). >>> >>> So If I understand correctly what you’re doing, you have a normal struct A, >>> at “runtime” with a transformer binding like normal structs have. >>> Then you have a compile-time struct B, which has prop:procedure and >>> prop:match-expander, where you want an instance of B to be the right-hand >>> side of a (define-syntax <identifier> (B ….))? Is that correct? And the >>> prop:procedure in B will expand to something like (A ….), and the >>> prop:match-expander in B will expand to (A ….) as a match pattern? Or am I >>> misunderstanding what you’re trying to do? > > > On Apr 15, 2015, at 11:02 PM, Jon Zeppieri <zeppi...@gmail.com> wrote: > >> You got it. > > So do you want to put a contract on the instance of B, or do you want to put > a contract on what it expands to?
What it expands to, with correct blame ascription. > > If you want to put it on what it expands to, then you could look at this: > http://docs.racket-lang.org/syntax/exprc.html > Or this: > http://docs.racket-lang.org/unstable/wrapc.html Thanks, I'll take a look. > > By the way, why wouldn’t you just use define-match-expander instead of > defining the B struct? > > Because I need the same identifier to expand either to a procedure or to a match expander, and I don't know how to do that using define-match-expander. -Jon -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
