Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!samsung!munnari.oz.au!goanna!ok
From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.lang.prolog
Subject: Re: Object Oriented Prolog question
Message-ID: <4850@goanna.cs.rmit.oz.au>
Date: 28 Feb 91 03:01:19 GMT
References: <1991Feb19.093713.4151@ecrc.de> <29107@cs.yale.edu>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 19

In article <29107@cs.yale.edu>, ciancarini-paolo@cs.yale.edu (paolo ciancarini) writes:
> Just as a matter of curiosity, what is a "coroutining system"
> if it is not a system of things with independent states (i.e. objects) ?

A "coroutining" Prolog is one which is capable of executing goals out of
order.  That is, if we have
	p :- q, r.
	q :- a, b.
	r :- c, d.
(ignoring parameters), then the query
	?- p.
may be solved in the order c, b, d, a.  There is *nothing* in here
corresponding to a mutable state, there are *no* objects (no notion
of "object identity" is useful or definable, and without object
identity you haven't got objects).  In fact, coroutining Prologs
encourage pure coding, because it is hard to rely on the execution order
of side-effective commands like assert/1 and retract/1.
-- 
The purpose of advertising is to destroy the freedom of the market.