Newsgroups: comp.lang.prolog
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From: fjh@munta.cs.mu.OZ.AU (Fergus Henderson)
Subject: Re: HELP: Write my own setarg/3
Message-ID: <9511322.15946@mulga.cs.mu.OZ.AU>
Sender: news@cs.mu.OZ.AU (CS-Usenet)
Organization: Computer Science, University of Melbourne, Australia
References: <1995Apr21.095703.1@vax.sbu.ac.uk>
Date: Sun, 23 Apr 1995 12:22:39 GMT
Lines: 17

zhuhail@vax.sbu.ac.uk writes:

>I realy need setarg/3 to update the arguments. However my system hasn't
>got it! Do you, expert, know how to write setarg/3 of my own? Or, tell
>me this is not possible:-)

Generally if you don't have setarg/3 it is not possible to write your
own.  setarg/3 performs backtrackable destructive assignment, and in
order to implement it you need at least some primitive that performs
destructive assignment.  I don't know of any Prolog system that provide
a primitive to perform destructive assignment but does not provide
setarg/3.

-- 
Fergus Henderson            | Tell you what: go write a 100x100 matrix multiply
fjh@cs.mu.oz.au             | of integers in both languages and then let's talk
http://www.cs.mu.oz.au/~fjh | about speed, ok? - Tom Christiansen.
