root/tags/lgt290/library/integer.lgt

:- object(integer,
    extends(number)).


    :- info([
        version is 1.0,
        authors is 'Paulo Moura',
        date is 2000/7/24,
        comment is 'Integer data type predicates.']).


    :- public(between/3).

    :- mode(between(+integer, +integer, ?integer), zero_or_more).

    :- info(between/3, [
        comment is 'Returns integers in the interval defined by the two first arguments.',
        argnames is ['Lower', 'Upper', 'Integer']]).


    between(Lower, Upper, Integer) :-
        integer(Lower),
        integer(Upper),
        (var(Integer) ->
            Lower =< Upper,
            generate(Lower, Upper, Integer)
            ;
            integer(Integer),
            Lower =< Integer,
            Integer =< Upper).


    generate(Lower, _, Lower).

    generate(Lower, Upper, Integer) :-
        Lower < Upper,
        Next is Lower + 1,
        generate(Next, Upper, Integer).


    valid(Integer) :-
        integer(Integer).


:- end_object.