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From: dowding@ai.sri.com (John Dowding)
Newsgroups: comp.lang.prolog
Subject: Re: Quintus Prolog Problem
Message-ID: <DOWDING.90Nov13152422@palm.ai.sri.com>
Date: 13 Nov 90 23:24:22 GMT
References: <264@messina.cs.utexas.edu>
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In-reply-to: bradley@cs.utexas.edu's message of 13 Nov 90 22:35:16 GMT

In article <264@messina.cs.utexas.edu> bradley@cs.utexas.edu (Bradley L. Richards) writes:

   As near as I can tell, setof and bagof don't work properly with the
   "recorded" predicate in Quintus Prolog (version 2.5.1, sun3-4.0).

   If I record:  recorda(woof, term2, _),
		 recorda(woof, term1, _).

   and then query:  setof(X, recorded(woof, X, _), Set).

   I receive the answer Set = [term2], and on backtracking the answer
   Set - [term1].  It seems to me that I should receive a single answer
   Set - [term1, term2].

   Am I missing something?  Or is this a known bug?

   Bradley

It is trickey.  This would work:

	setof(X, Ref^recorded(woof, X, Ref), Set)

Prolog doesn't have a true don't-care variable.  The _ is really
just a shorthand for some particular variable that you haven't
bothered to name.  


John Dowding
dowding@ai.sri.com