Re: elementary problem (I hope)

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Article #4273

#4273

From: Todd J. Feldman
Date: Sat, 10 Mar 1990 12:01

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In article <1990Mar9.095655.4191@bath.ac.uk> ccsdgdc@gdr.bath.ac.uk (Douglas Clark) writes:
>
>A user has been asking me how to write synonyms in Prolog. Being ignorant
>I have no idea. It is obvious why the natural
>
>father(X):-male(X).
>male(X):-father(X).
>father(fred).
>
>fails. But I cannot find a substute that works. Some way of eliminating
>the repetitive backtracking. Help would be appreciated.

How about:

father(X):-
	not(tried(male(X))),
	assert(tried(male(X))),
	male(X).
male(X):-
	not(tried(father(X))),
	assert(tried(father(X))),
	father(X).

if you store any 'male' or 'father' facts, they will be detected, and any
infinite recursion will be prevented by the 'tried' facts.  Of course, you'd
need to be sure to clean up these 'tried' facts when you're done.


Todd

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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!uwm.edu!zaphod.mps.ohio-state.edu!wuarchive!decwrl!shelby!neon!feldman
From: feldman@Neon.Stanford.EDU (Todd J. Feldman)
Newsgroups: comp.lang.prolog
Subject: Re: elementary problem (I hope)
Message-ID: <1990Mar10.120125.12992@Neon.Stanford.EDU>
Date: 10 Mar 90 12:01:25 GMT
References: <1990Mar9.095655.4191@bath.ac.uk>
Sender: Todd J. Feldman(feldman@neon.stanford.edu)
Organization: Computer Science Department, Stanford University
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