Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!edcastle!aiai!ken
From: ken@aiai.ed.ac.uk (Ken Johnson)
Newsgroups: comp.lang.prolog
Subject: Re: Quintus Prolog Problem
Message-ID: <3751@skye.ed.ac.uk>
Date: 14 Nov 90 12:33:37 GMT
References: <264@messina.cs.utexas.edu>
Reply-To: ken@aiai.UUCP (Ken Johnson)
Organization: Bugs-R-Us
Lines: 36

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

You're missing something.  That's the correct behaviour.  Look again at
the incantation:

?- setof(X, recorded(woof, X, _), Set).

That anonymous variable will be given a different value on each
backtrack.  To state that you want all values to be included in Set, use
the existential quantifier and give the variable a name:

?- setof(X, Ref^recorded(woof, X, Ref), Set).

In general you should not use the anonymous variable anywhere inside a
setof or bagof unless you *know* what you are doing. 
-- 
Ken Johnson, AI Applications Inst., 80 South Bridge, Edinburgh EH1 1HN
       E-mail ken@aiai.ed.ac.uk,   ******************************************
phone 031-225 4464 extension 213   **  `You can resole your boot, but you  **
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