Path: utzoo!attcan!uunet!munnari.oz.au!csc.anu.oz.au!ada612
From: ada612@csc.anu.oz.au
Newsgroups: comp.lang.prolog
Subject: Re: PDC prolog gripe/question
Message-ID: <1990Oct29.133821.3194@csc.anu.oz.au>
Date: 29 Oct 90 03:38:20 GMT
Organization: Computer Services, Australian National University
Lines: 35

Re: Message-ID: <1990Oct21.155423.9467@canterbury.ac.nz>
    From: fore057@canterbury.ac.nz

>To be fair to the PDC, the professional users guide comes with over 7000
>lines of source code, on three disks.  Still, it would be nice to get the
>promised information on overlay linking without having to shell out an
>extra $350, especially as it would appear that purchase of a linker like
>PLink86 or RTLink would also be required.
>
>I guess we have to remember that PDC Prolog users are few (my serial number
>is just under 3,500 for version 3.2, and I upgraded recently).  The PDC
>developers have to eat somehow.  If I had the money to spend, I wouldn't
>quibble.

What is galling is not the $A350 price for the PCUG, but the fact that
it costs an extra $US110 or so over the American price of of $199.  If
PDC users are few, why on earth did they decide to attempt to sell the
product in Australia thru a bunch of people who charge more than half
the price of the product to do some mailing and currency conversions?
With distributors like that you don't need competitors.

As for overlays, I've found empirically that one can sometimes get away with
using public domain overlay linkers such as Michael Devore's OVL 3.12,
if the predicates that are called across overlay boundaries are declared
as c predicates, and the program is linked as a mixed prolog & c program.
(you will probably also need to customize the stkln parameter at the
begininning of tcmain, to get a reasonable size of stack).
But it isn't reliable, for reasons that are  unclear to me: minor
rearrangements of the source code seem to affect whether overlays
work or not.  Perhaps the PCUG would reveal what is actually going on.
Also, someone who actually knew the gory details of how overlays work
on PCs might be able to improve on the results of my rather blind and
ignorant hacking.

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