Re: retractall and backtracking

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Article #216

#216

From: Joaquim Baptista (pxQuim)
Date: Tue, 13 Jun 1989 02:50

39 lines
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In article <10539@burdvax.PRC.Unisys.COM> armagan@PRC.Unisys.COM (Armagan Ozdinc) writes:

   In article <PX.89Jun9194119@uniq.unl.fctunl.rccn.pt>, Joaquim Baptista writes:
   > 
   > Variations on this problem also arise with asserta and assertz, as in:
   > 
   > /* this will loop forever, exhausting your heap space,
   >    writing 1211111111... */
   > 	b(1). b(2).
   > 	exec2:- b(X), write(X), assertz(b(X)), fail.
   > 

   In Quintus Prolog 2.4, exec2 doesn't behave as you describe above. It
   prints 12 and fails.

   Armagan Ozdinc
   Unisys Corporation
   Paoli Research Center

One of the postings on this subject mentioned that Quintos Prolog has
the nice property of 'freezing' the definition of a predicate when you
call it, which seems nice to me. This is a solution to the
assert/retract semantics that I had never heard of.

However, Prolog-2 for IBM PC and C-Prolog will behave as I said. I
believe Arity/Prolog will do that as well, but I'me not completely
sure.
--
--------

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Path: arc1-ca.pugleaf.net!utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!mcvax!inesc!unl!om!px
From: px@unl.fctunl.rccn.pt (Joaquim Baptista (pxQuim))
Newsgroups: comp.lang.prolog
Subject: Re: retractall and backtracking
Message-ID: <PX.89Jun13025034@om.unl.fctunl.rccn.pt>
Date: 13 Jun 89 02:50:34 GMT
References: <575@hfserver.hfnet.bt.co.uk> <PX.89Jun9194119@uniq.unl.fctunl.rccn.pt> <10539@burdvax.PRC.Unisys.COM>
Sender: px@unl.fctunl.rccn.pt
Organization: Universidade Nova de Lisboa, Portugal
Lines: 39
In-reply-to: armagan@PRC.Unisys.COM's message of 12 Jun 89 14:09:24 GMT
Posting-Front-End: GNU Emacs 18.44.13 of Wed Jun 24 1987 on om (berkeley-unix)

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