Path: utzoo!mnetor!uunet!husc6!mailrus!nrl-cmf!ames!lll-tis!mordor!sri-spam!sri-unix!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.lang.prolog
Subject: Re: Ranges of values in Cprolog
Message-ID: <933@cresswell.quintus.UUCP>
Date: 6 May 88 00:23:53 GMT
References: <242@yetti.UUCP>
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 54

In article <242@yetti.UUCP>, asst-jos@yetti.UUCP (Jonathan) writes:
> 	I am working with C-prolog 1.5, and have implemented the following
> predicate for sets. (I use lists to implement sets)
[code for member/2, written as an infix 'in']

> I would [like] to implement this 'in' operator to allow for the following:
> (The '..' would have the same meaning as it does in Pascal).
> ?- X in [1 .. 100].
> Unfortunately, I keep running into problems when attempting this, and I am 
> tired of hitting my head against a brick wall. Any suggestions???

If you didn't get the CProlog version of the DEC-10 Prolog library with
your copy of CProlog, ask whoever you got your CProlog licence from to
explain why not.  If you _did_ get the library, you'll find a predicate
	between(LowerBound, UpperBound, X) <->
		all arguments integer & LowerBound <= X <= UpperBound
and you can adapt that.

You'll need to define your 'in' a little bit more clearly.
What, if anything, should
	c in [1..10,alpha..gamma,no(c)]
do?

It is rather ugly to have a list whose elements are not of the same
"type", and 5 and 4..6 seem to me to be of different "types".  A clean
approach to the design of such a data structure might go like this:

a <integer set> can be		% type intset -->
	an <empty> set		%	{}
	a <singleton> set	%    |	{integer}
	an <interval>, or	%    |	integer..integer
	a <union> of two sets.	%    |  intset + intset

Coding this, we obtain

	:- current_op(Prio, yfx, *), op(Prio, xfx, ..).
	:- current_op(Prio, xfx, <), op(Prio, xfx, in).

	:- lib(between).		% CProlog 1.5.edai
	:- compile(library(between)).	% Quintus Prolog

	in(Element, Set) :-
		in1(Set, Element).

	in1({Element}, Element).
	in1(Low..High, Element) :-
		between(Low, High, Element).
	in1(Set+_,     Element) :-
		in1(Set, Element).
	in1(_+Set,     Element) :-
		in1(Set, Element).

This works just fine in Quintus Prolog (e.g. "X in {1}+2..4+{5}"
enumerated the results 1,..,5).  What are the problems you keep running into?