root/trunk/examples/assignvars/rectangle3.lgt

:- object(rectangle(_Width, _Height, _Position),
    imports(private::assignvars)).

    :- info([
        version is 1.0,
        author is 'Paulo Moura',
        date is 2005/1/8,
        comment is 'A simple implementation of a geometric rectangle using assignable variables and parametric objects.',
        parnames is ['Width', 'Height', 'Position']]).

    :- public(init/0).
    :- mode(init, one).
    :- info(init/0,
        [comment is 'Initialize rectangle position.']).

    :- public(area/1).
    :- mode(area(-integer), one).
    :- info(area/1,
        [comment is 'Rectangle area.',
         argnames is ['Area']]).

    :- public(move/2).
    :- mode(move(+integer, +integer), one).
    :- info(move/2, [
        comment is 'Moves a rectangle to a new position.',
        argnames is ['X', 'Y']]).

    :- public(position/2).
    :- mode(position(?integer, ?integer), zero_or_one).
    :- info(position/2, [
        comment is 'Rectangle current position.',
        argnames is ['X', 'Y']]).

    init :-
        parameter(3, Position),
        ::assignable(Position, (0, 0)).

    area(Area) :-
        parameter(1, Width),
        parameter(2, Height),
        Area is Width*Height.

    move(X, Y) :-
        parameter(3, Position),
        ::Position <= (X, Y).

    position(X, Y) :-
        parameter(3, Position),
        ::Position => (X, Y).

:- end_object.