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From: ada612@csc.anu.edu.au
Newsgroups: comp.lang.prolog
Subject: Re: Environments
Message-ID: <1991Mar28.113930.1@csc.anu.edu.au>
Date: 28 Mar 91 00:39:30 GMT
Article-I.D.: csc.1991Mar28.113930.1
Sender: news@newshost.anu.edu.au
Organization: Computer Services, Australian National University
Lines: 37

In article <5044@goanna.cs.rmit.oz.au>,
ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe) writes:

++As it happens, the system I was using was Turbo Prolog 2.something
++There was one phase of the program which needed a lot of space in
++area A, but very little in area B.  A later phase needed a lot of
++space in area B, but very little in area A.  It turned out to be
++impossible to find a single static allocation which was adequate
++for both phases.  So I just couldn't run my program.  Why?  Because
++of an entirely ARTIFICIAL restriction.  There was more than enough
++space on the machine to do the job.  (In fact ALS Prolog just flew
++through it.)  But because Turbo's implementors had seen fit to
++unload part of *their* job onto the paying customer, the system was
++not usable.

What kind of black magic is ALS Prolog employing here?  The impression
I get from the Jan 91 issue of AI Expert is that Arity, PDC (formerly
Turbo), Quintus, & ALS Prologs for MS-DOS all suffer from annoying
restrictions on memory, and that Turbo (now PDC) is for the most part less
limited than the others in this respect.  Everybody seems to have to make
nasty compromises to shoehorn Prolog into MSDOS, and I wonder if Richard's
program wasn't merely one where ALS's deal with the devil just happened
to work out while PDC's didn't.

Some anecdotal evidence that PDC is pretty economical with memory is that
I have managed to write in it an LFG grammar-development  system for
students learning linguistics which includes a built in editor, simple
morphology & lots of notational sugar for the rules and lexical entries.
A similar system written in 1986-vintage Arity Prolog at Stuttgart seems
to fill up the machine without providing any of these features (`Edit'
appears on the menu, but there's a `no space' apology rather than an actual
integrated editor). (The design of their parsing system plus the fact that
they used overlays makes it unlikely that this is because their approach
was inherently more memory-intensive than mine. I would in fact expect the
opposite to be true.)

   Avery Andrews (ada612@csc.anu.edu.oz)