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