On Sat, 12 Jun 2004, Matthias Radestock wrote:

>> (define (force promise)
>>    (let ((content (unbox (unbox promise))))
>>      (case (car content)
>>        ((eager) (cdr content))
>>        ((lazy)  (let* ((promise* ((cdr content)))
>>                        (content  (unbox (unbox promise))))
>
> Shouldn't that last line use promise*? If so, how come your tests pass?

No.  It is correct as it stands.  The evaluation of ((cdr content)) in the
previous line may update the content of the original promise passed to
*force* in case of reentrancy.  This is exact what happens in reentrancy
test 3 contributed by John Shutt.

Regards
Andre