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yap-6.3/Logtalk/examples/shapes/ph/ph.lgt

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:- object(shape). % an object with no hierarchy relations with other
% objects is always compiled as a prototype
:- info([
author is 'Paulo Moura',
version is 1.0,
date is 2003/2/3,
comment is 'Generic geometric shape.']).
:- public(color/1).
:- mode(color(?atom), zero_or_one).
:- info(color/1, [
comment is 'Shape color.',
argnames is ['Color']]).
:- public(position/2).
:- mode(position(?integer, ?integer), zero_or_one).
:- info(position/2, [
comment is 'Shape position.',
argnames is ['X', 'Y']]).
color(red). % default shape color
position(0, 0). % default shape position
:- end_object.
:- object(polygon,
extends(shape)).
:- info([
author is 'Paulo Moura',
version is 1.1,
date is 2004/1/8,
comment is 'Generic polygon.']).
:- public(nsides/1).
:- mode(nsides(?integer), zero_or_one).
:- info(nsides/1, [
comment is 'Polygon number of sides.',
argnames is ['Number']]).
:- public(area/1).
:- mode(area(-float), zero_or_one).
:- info(area/1, [
comment is 'Polygon area.',
argnames is ['Area']]).
:- public(perimeter/1).
:- mode(perimeter(?atom), zero_or_one).
:- info(perimeter/1, [
comment is 'Polygon perimeter.',
argnames is ['Perimeter']]).
:- end_object.
:- object(regular_polygon,
extends(polygon)).
:- info([
author is 'Paulo Moura',
version is 1.1,
date is 2004/1/8,
comment is 'Generic regular polygon.']).
:- public(side/1).
:- mode(side(?atom), zero_or_one).
:- info(side/1, [
comment is 'Regular polygon side length.',
argnames is ['Length']]).
side(1). % default side length
perimeter(Perimeter) :-
::nsides(Number),
::side(Side),
Perimeter is Number*Side.
:- end_object.
:- object(square,
extends(regular_polygon)).
:- info([
author is 'Paulo Moura',
version is 1.0,
date is 2003/2/3,
comment is 'Geometric square.']).
nsides(4).
area(Area) :-
::side(Side),
Area is Side*Side.
:- end_object.
:- object(q1,
extends(square)).
:- end_object.
:- object(q2,
extends(square)).
position(2, 3).
color(blue).
side(3).
:- end_object.