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From: milgr@teapot.prime.COM (Marc Milgram)
Newsgroups: comp.lang.prolog
Subject: Re: Novice RETRACT question
Message-ID: <728@primerd.PRIME.COM>
Date: 31 Jul 90 17:02:48 GMT
References: <1939@engage.enet.dec.com>
Sender: news@primerd.PRIME.COM
Reply-To: milgr@teapot.prime.COM (Marc Milgram)
Lines: 29

In article <1939@engage.enet.dec.com>, ssmith@ncdel.enet.dec.com
(Sheldon E. Smith) writes:
|>I'm playing with a program that generates a *load* of facts.  Many of
|>the facts are "time-stamped", so quite a few facts are duplicate or
obsolete. 

|>reduce_objects :- object(I,X,Y),object(J,X,Y),
|>		I < J,
|>		retract(object(I,X,Y)).


Alternately, you could do this at assert time with:

assert_unique_object(object(I, X, Y)):-
	not(( retract(object(_, X, Y), fail)),
	assert(object(I, X, Y)).

|>------------------------------------------------------------------------
|>---------
|>Sheldon E. Smith			!Email:
|>Digital Equipment Corporation		! ssmith%ncdel.enet.dec@decwrl.dec.com
|>Minneapolis, Minnesota			! ...!decwrl!ncdel.enet.dec.com!ssmith
|>========================================================================
|>=========
                                

Marc Milgram		Email: milgr@teapot.prime.com
Prime Computer
Framingham, MA