% File : BETWEEN.PL
% Author : R.A.O'Keefe
% Updated: 4 October 1984, 11-8-87
% Purpose: Generate integers.
between(L, U, N) :-
	nonvar(N),
	!,
	integer(L),
	integer(U),
	integer(N),
	L =< N, N =< U. between(L, U, N) :-
	integer(L),
	integer(U),
	L =< U, between1(L, U, N). between1(L, _, L).
between1(L, U, N) :-
	L < U, M is L+1, between1(M, U, N). % gen_arg(N, Term, Arg)
% is exactly like arg(N, Term, Arg), except that it will generate
% solutions for N by backtracking (will work when N is a variable).
gen_arg(N, Term, Arg) :-
	functor(Term, _, Arity),
	between(1, Arity, N),
	arg(N, Term, Arg).
% Original by R O'Keefe
%
% gen_nat(+X)	 True if X is a natural number, false otherwise
% gen_nat(-X)	 Instantiates X to 0, then 1, 2, 3, 4...
%
% gen_nat(+L,-N) Instantiates N to L, then L+1, L+2...
% gen_nat(+L,+N) True if N>= L
% gen_nat(-L,+N) ** Succeeds with L = N , then LOOPS **
%
% gen_int(-X)	 Instantiates X to 0, then 1, -1, 2, -2, 3, -3...
gen_nat(N) :-			% gen-erate nat-ural
	nonvar(N),		% if we aren't to generate it
	!,			% demand that it
	integer(N),		% be an integer
	N>= 0.			% and non-negative.
gen_nat(N) :-			% otherwise, generate an
	gen_nat(0, N).		% integer>= 0
 
 
gen_nat(L, L).
gen_nat(L,N) :-			% Bug fix Ken Johnson 6-5-87
	nonvar(L),		% Where both args are instantiated
	nonvar(N),		% just test N>= L.
	integer(L),		% Avoids an infinite loop
	integer(N),		% where N < L
	!,
	N>= L.
gen_nat(L, N) :-		% generate natural> L
	succ(L,M),
	gen_nat(M, N).		% generate natural>= M
 
 
gen_int(I) :-			% gen-erate int-eger
	nonvar(I),		% if we aren't to generate it
	!,			% demand that it is an integer.
	integer(I).
gen_int(0).			% generate 0
gen_int(I) :-			% generate +/- N for N> 0
	gen_nat(1, N),
	( I = N
	; I is -N
	).