72b037275f
git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1288 b08c6af1-5177-4d33-ba66-4b1c6b8b522a
71 lines
1.2 KiB
Plaintext
71 lines
1.2 KiB
Plaintext
/*
|
|
This example illustrates the use of the predicate directive alias/3 for
|
|
defining alternative names for inherited predicates.
|
|
*/
|
|
|
|
|
|
% first, we define a simple parametric object for representing rectangles:
|
|
|
|
:- object(rectangle(_Width, _Height)).
|
|
|
|
:- public(width/1).
|
|
:- public(height/1).
|
|
:- public(area/1).
|
|
|
|
width(Width) :-
|
|
parameter(1, Width).
|
|
|
|
height(Height) :-
|
|
parameter(2, Height).
|
|
|
|
area(Area) :-
|
|
::width(Width),
|
|
::height(Height),
|
|
Area is Width*Height.
|
|
|
|
:- end_object.
|
|
|
|
|
|
% next, we define a square object which adds an alias, side/1, for the
|
|
% inherited predicate width/1:
|
|
|
|
:- object(square(Side),
|
|
extends(rectangle(Side, Side))).
|
|
|
|
:- alias(rectangle(_, _), width/1, side/1).
|
|
|
|
:- end_object.
|
|
|
|
|
|
% a similar example can be defined using ellipses and circles:
|
|
|
|
:- object(ellipse(_RX, _RY)).
|
|
|
|
:- public(rx/1).
|
|
:- public(ry/1).
|
|
:- public(area/1).
|
|
|
|
rx(Rx) :-
|
|
parameter(1, Rx).
|
|
|
|
ry(Ry) :-
|
|
parameter(2, Ry).
|
|
|
|
area(Area) :-
|
|
::rx(Rx),
|
|
::ry(Ry),
|
|
Area is Rx*Ry*3.1415927.
|
|
|
|
:- end_object.
|
|
|
|
|
|
% in this case, we define an alias named r/1 for the inherited
|
|
% predicate rx/1:
|
|
|
|
:- object(circle(Radius),
|
|
extends(ellipse(Radius, Radius))).
|
|
|
|
:- alias(ellipse(_, _), rx/1, r/1).
|
|
|
|
:- end_object.
|