:- object(rectangle(_Width, _Height)).
:- info([
author is 'Paulo Moura',
version is 1.0,
date is 2000/4/22,
comment is 'Parametric object for representing geometric rectangles.',
parnames is ['Width', 'Height']]).
:- public(width/1).
:- mode(width(?number), zero_or_one).
:- info(width/1, [
comment is 'Rectangle width.',
argnames is ['Width']]).
:- public(height/1).
:- mode(height(?number), zero_or_one).
:- info(height/1, [
comment is 'Rectangle height.',
argnames is ['Height']]).
:- public(area/1).
:- mode(area(-number), one).
:- info(area/1, [
comment is 'Rectangle area.',
argnames is ['Area']]).
width(Width) :-
parameter(1, Width).
height(Height) :-
parameter(2, Height).
area(Area) :-
::width(Width),
::height(Height),
Area is Width*Height.
:- end_object.
