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From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.lang.prolog
Subject: Re: Interesting exercise / NeXT machines
Message-ID: <4765@goanna.cs.rmit.oz.au>
Date: 13 Feb 91 06:35:42 GMT
References: <1991Feb12.013413.24312@cs.ubc.ca>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 21

In article <1991Feb12.013413.24312@cs.ubc.ca>, poole@cs.ubc.ca (David Poole) writes:

> 1. Does anyone know whether there is a Prolog that runs on NeXT computers.

You may be able to run binaries from some other 680x0 machines.
Or try SB Prolog (but not _too_ hard).

> 2. I recently had the need for an efficient implementation of a
> priority queue. I wanted to add and remove element in log n time.  The
> "normal" way (using an array called a "heap") that is taught in
> computer science courses is inappropriate for Prolog.

Wrong.  Heaps work very nicely indeed in Prolog.  A file called HEAPS.PL
is available in the DEC-10 Prolog library (see library(heaps) in the
Quintus library).  Your mistake is in identifying "heaps" with one
particular *IMPLEMENTATION* of heaps using arrays.  A heap is just a
node-labelled binary tree with a constraint on the labels.  I wouldn't
go so far as to call this a trivial exercise, but it's not far off it.

-- 
Professional programming is paranoid programming