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From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.lang.prolog
Subject: Re: The Craft of Prolog pp. 126-130
Message-ID: <4201@goanna.cs.rmit.oz.au>
Date: 5 Nov 90 04:37:39 GMT
References: <4473@swi.swi.psy.uva.nl>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 26

In article <4473@swi.swi.psy.uva.nl>, anjo@swi.psy.uva.nl (Anjo Anjewierden) writes:
> If you study the remainder of the book it is not at all difficult
> to see what is wrong with this program: why is the partial solution
> represented as a list?

Answer:  we have a number with 9 decimal digits.  I am aware of Prolog
systems with 14-bit, 16-bit, 17-bit, 18-bit, 20-bit, 24-bit, 28-bit,
29-bit, and 32-bit integer arithmetic, as well as logical arithmetic
(by which I mean arithmetic with no stupid bit bound).  How large can
an integer with 9 distinct decimal digits get?
	987654321
How many bits does this need?
	30
Will that _work_ in the Prolog systems I was using at the time?
	a certain Prolog interpreter on a Sun-3/50	: NO
	a certain Prolog compiler on a Sun-3/50		: NO
	a certain Prolog compiler on a PC		: NO
	another Prolog compiler on a PC			: NO
So _could_ I have used Anjewierden's method?
	No.

Recite after me:  "not every Prolog system provides 32-bit integers".

-- 
The problem about real life is that moving one's knight to QB3
may always be replied to with a lob across the net.  --Alasdair Macintyre.