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Re: [Chicken-hackers] clarification of multiple evaluation of promises


From: Jörg F . Wittenberger
Subject: Re: [Chicken-hackers] clarification of multiple evaluation of promises
Date: 13 May 2013 10:29:34 +0200

On May 13 2013, Jörg F. Wittenberger wrote:

Peter Bex has pointed out that my example in
http://lists.nongnu.org/archive/html/chicken-hackers/2013-05/msg00031.html
was not very clear about the problem at hand; let my clarify.
...
NB: Things would be even stranger, if we would cause the promise "p"
   to raise an exception for most results of (random 1000).

Thus `delay` and `force` behave as my intuition would suggest
*only* if `force` is called from the same thread, which produced
the promise using `delay`.

Attached a test case, which shows that promises raising exceptions
are also evaluated more than once, even when there is only the
primordial thread involved.

According to my understanding this clearly violates at least the
r7rs draft.


Best

/Jörg


.......

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