Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!rpi!leah!bingvaxu!vu0310
From: vu0310@bingvaxu.cc.binghamton.edu (R. Kym Horsell)
Newsgroups: comp.lang.prolog
Subject: Re: Arrays in Prolog
Message-ID: <3899@bingvaxu.cc.binghamton.edu>
Date: 27 Aug 90 21:20:07 GMT
References: <90239.175243SCHMIED@DB0TUI11.BITNET>
Reply-To: vu0310@bingvaxu.cc.binghamton.edu.cc.binghamton.edu (R. Kym Horsell)
Organization: SUNY Binghamton, NY
Lines: 34

In article <90239.175243SCHMIED@DB0TUI11.BITNET> SCHMIED@tubvm.cs.tu-berlin.de (Albrecht Schmiedel) writes:
\\\
>My questions are the following:
>1) Are there Prologs that adress this kind of need?
>   (I.e. Prologs that make assertions, retractions, and calls
>   involving  predicates that fulfill certain conditions
>   - for example, a guaranteed instantiated integer as its first
>   argument, one clause per integer, no backtracking -
>   similarly fast as array operations.)
>2) Are there Prologs which are easily extendable by predicates
>   written in C that could do the job?
>   (It should be possible to pass *terms* back and forth;
>   having to decompose terms and lists before processing them
>   by a foreign language predicate and then having to put them
>   together again later on is definitely not what we want.)
>3) Shouldn't we be using Prolog?
>4) Is there a 'Prolog-way' of handling large graphs efficiently?
>   (Graphs where data referencing other nodes is attached to nodes,
>   and search as well as updates are required.)

So it's come to this -- destructive assignment in Prolog!

There are several methods for implementing arrays in Prolog
and the one I have implemented is a variant of the setarg/3
precicate that also appears elsewhere.

setarg(Index,Term,Value)

replaces argument ``index'' in ``term'' with ``value'' but
allows backtracking so that ``term'' may be restored to its
former state -- no destructuve assignment happens unless you
	setarg(X,Y,Z), !.

-Kym Horsell