On Sun, 11 Mar 2007, R. Kent Dybvig wrote:
Okay, here's one example:
(library (L1)
(export y get-y set-y!)
(import (r6rs))
(define x (call/cc (lambda (k) (list 0 k values))))
(define y (car x))
(define z ((caddr x)))
(define get-y (lambda () y))
(define set-y!
(lambda (v)
(call/cc (lambda (k) ((cadr x) (list v (cadr x) k)))))))
I think there is an error. Here is a working version:
(library (L1)
(export y get-y set-y!)
(import (r6rs))
(define x (call/cc (lambda (k) (list 0 k values))))
(define y (car x))
(define z ((caddr x) #f)) ; modified line
(define get-y (lambda () y))
(define set-y!
(lambda (v)
(call/cc (lambda (k) ((cadr x) (list v (cadr x) k)))))))
By my reading of the current library description, the program:
(import (r6rs) (L1))
(write (list y (get-y))) (newline)
(set-y! 3)
(write (list y (get-y))) (newline)
prints
(0 0)
(0 3)
I get the following, which I think is also consistent with the current
specification:
(0 0)
(3 3)
This happens if exported variables are translated to shared r5rs toplevel
globals, which is a possible implementation of the shared semantics.
Andre
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