After chatting with samth, I know the deal here.
Provided identifiers are only the same in symbol, but not free-identifier=?.
provide/contract creates mangled identifiers and provides them rename-out'd to
the original identifier. This does NOT make the provided identifier
free-identifier=? to the original - they are free-identifier=? to the mangled
ids.
The way I went about fixing this was to use an unhygienic macro so that I could
capture that mangled id when expanding in the other module.
(define-syntax (myprovide stx)
(syntax-case stx ()
[(_ param)
(with-syntax ([mystruct (datum->syntax #'param 'mystruct)])
#'(begin (provide/contract [a param])
(provide (struct-out mystruct))))]))
-Ian
----- Original Message -----
From: "J. Ian Johnson" <i...@ccs.neu.edu>
To: "users" <users@racket-lang.org>
Sent: Wednesday, July 20, 2011 8:42:05 PM GMT -05:00 US/Canada Eastern
Subject: [racket] Re-providing contracted structs?
I have a strange bug I can't figure out dealing with re-providing a struct that
was contracted in my require.
Module A:
Firstly, I have a specific contract for my struct:
(provide/contract (struct mystruct ([field integer?])))
I have another part of A I will contract later:
(provide a)
I have several other modules that give a, b and c in module A different
contracts, but only slightly, so I have a macro for it in module A.
(define-syntax-rule (myprovide param)
(begin (provide/contract [a param])
(provide (struct-out mystruct))))
Module B:
[require module A]
(myprovide any/c)
ERROR:
struct-out: no binding for structure-type identifier at: mystruct in:
(struct-out mystruct)
This works if Module A just does (provide (struct-out mystruct)), but I don't
want that.
Is it really the case that I can't re-export this struct using struct-out, or
is there a bug in provide/contract?
-Ian
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