2010/11/13 김태윤 <[email protected]>:
> [...]
> I was told by mailing list that read the racket guide unit section
> but sorry I still don't understand.
> [...]
Hello,
you have to use units here because modules do not allow mutually recursive
dependencies. An example for your situation may look like this:
-----BEGIN "ab-sig.rkt"-----
#lang racket
(define-signature a^
(a))
(define-signature b^
(b))
(provide
(all-defined-out))
-----END "ab-sig.rkt"-----
-----BEGIN "a.rkt"-----
#lang racket
(require
"ab-sig.rkt")
(define-unit a@
(import b^)
(export a^)
(define a 1)
(printf "a@ sees b = ~s~%" b))
(provide
(all-defined-out))
-----END "a.rkt"-----
-----BEGIN "b.rkt"-----
#lang racket
(require
"ab-sig.rkt")
(define-unit b@
(import a^)
(export b^)
(define b 2)
(printf "b@ sees a = ~s~%" a))
(provide
(all-defined-out))
-----END "b.rkt"-----
-----BEGIN "ab.rkt"-----
#lang racket
(require
"ab-sig.rkt" "a.rkt" "b.rkt")
(define-values/invoke-unit/infer
(export a^ b^)
(link a@ b@))
(printf "ab.rkt sees a = ~s~%" a)
(printf "ab.rkt sees b = ~s~%" b)
-----END "ab.rkt"-----
As you can see, the module dependencies are cycle free but the unit dependency
between a@ and b@ is mutual.
Note that, even though a@ and b@ can see each other's variables exported through
the signatures a^ and b^ respectively, the units still have to be initialized
in some order and hence one of the printf calls in a@ or b@ will show an
undefined value when "ab.rkt" is run.
I hope this helps :-)
Ciao,
Thomas
--
When C++ is your hammer, every problem looks like your thumb.
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