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From: tim@linc.cis.upenn.edu (Tim Finin)
Newsgroups: comp.lang.prolog
Subject: Re: Counting things.
Message-ID: <1424@super.upenn.edu.upenn.edu>
Date: Fri, 3-Jul-87 09:35:43 EDT
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Posted: Fri Jul  3 09:35:43 1987
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Counting the number of clauses in the DB unifying with a given term
using SETOF/BAGOF is the "proper" way to do it.  The other way this
sort of thing is typically done it to use ASSERT/RETRACT to keep a
counter in the DB and use a failure driven loop to find all the 
matches, as in:

	countClauses(X,_) :-
		assert(count(0)),
		clause(X,true),
		retract(count(N)),
		N2 is N+1,
		assert(count(N2)),
		fail.

	countClauses(_,N) :- retract(counter(N)).

There is, as I recall, a definition of a predicate FINDALL in C&M
which is similar to BAGOF and SETOF.

Tim