Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!umich!ox.com!itivax!dhw
From: dhw@itivax.iti.org (David H. West)
Newsgroups: comp.lang.prolog
Subject: Re: incrementing values
Message-ID: <4884@itivax.iti.org>
Date: 2 Feb 90 19:32:52 GMT
References: <17467@megaron.cs.arizona.edu> <31462@shemp.CS.UCLA.EDU> <34699@iuvax.cs.indiana.edu> <17483@megaron.cs.arizona.edu>
Reply-To: dhw@itivax.UUCP (David H. West)
Organization: Industrial Technology Institute
Lines: 15

In article <17483@megaron.cs.arizona.edu> debray@cs.arizona.edu (Saumya K. Debray) writes:
>> | 	increment(Variable) :-
>> | 		retract(value(Variable, OldValue)),
>> | 		NewValue is OldValue + 1,
>> | 		assert(value(Variable, NewValue)).
 
>Somehow "X1 is X+1" seems so much simpler!

Indeed.  But neither X nor X1 can be global, so you can sometimes
end up adding pairs of extra arguments to clauses just to provide
a data path for each such variable.  If this spans enough levels, it
may be worth using the admittedly ugly database method above.  I've
used it to quickly add and remove clause-invocation counting.

-David West  dhw@iti.org