Logtalk 2.27.1 files.

git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1580 b08c6af1-5177-4d33-ba66-4b1c6b8b522a

Logtalk/examples/proxies/NOTES

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+=================================================================
+Logtalk - Object oriented extension to Prolog
+Release 2.27.1
+
+Copyright (c) 1998-2006 Paulo Moura.  All Rights Reserved.
+=================================================================
+
+
+To load this example and for sample queries, please see the SCRIPT file.
+
+A parametric object may be used to represent objects whose "state" is static 
+and set when the object is defined. However, there can be only one parametric 
+object with a given functor and arity. For example, if we define the following
+parametric object:
+
+	:- object(circle(_Radius, _Color)).
+		...
+	:- end_object.
+
+then the following terms may be interpreted as references to the object above:
+
+	circle(1, blue)
+	circle(2, yellow)
+
+In the context of parametric objects, the above terms are know as "parametric 
+object proxies". Proxies represent different instantiations of a parametric 
+object parameters. They may be stored on the database as Prolog facts. This 
+results in a very compact representation, which can be an advantage when 
+dealing with a large number of objects. However, this is also a fragile 
+solution as changes on the parametric object ancestors may imply changes to 
+the number and meaning of the parametric object parameters which, in turn, 
+may imply changes to all the Prolog facts used to represent the individual 
+objects.

Logtalk/examples/proxies/SCRIPT

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+=================================================================
+Logtalk - Object oriented extension to Prolog
+Release 2.27.1
+
+Copyright (c) 1998-2006 Paulo Moura.  All Rights Reserved.
+=================================================================
+
+
+% start by loading the example:
+
+| ?- logtalk_load(proxies(loader)).
+...
+
+
+% print the area and the perimeter for all circle proxies:
+
+| ?- forall(circle(Id, R, C), (write(Id), write(' '), circle(R, C)::print)).
+
+#1 area: 4.75291, perimeter: 7.72831, color: blue
+#2 area: 43.2412, perimeter: 23.3106, color: yellow
+#3 area: 0.477836, perimeter: 2.45044, color: green
+#4 area: 103.508, perimeter: 36.0655, color: black
+#5 area: 217.468, perimeter: 52.2761, color: cyan
+yes

Logtalk/examples/proxies/loader.lgt

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+
+:- initialization(
+	logtalk_load(
+		[proxies])). 
+
+/*
+If you intend to use the FOP XSL:FO processor for generating PDF documenting
+files, comment the directive above and uncomment the directive below
+
+:- initialization(
+	logtalk_load(
+		[proxies], [xmlsref(standalone)])).
+*/

Logtalk/examples/proxies/proxies.lgt

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+
+:- object(circle(_Radius, _Color)).
+
+	:- public([
+		radius/1,
+		color/1,
+		area/1,
+		perimeter/1,
+		print/0]).
+
+	radius(Radius) :-
+		parameter(1, Radius).
+
+	color(Color) :-
+		parameter(2, Color).
+
+	area(Area) :-
+		::radius(Radius),
+		Area is 3.1415927*Radius*Radius.
+
+	perimeter(Perimeter) :-
+		::radius(Radius),
+		Perimeter is 2*3.1415927*Radius.
+
+	print :-
+		area(Area), write('area: '), write(Area),
+		perimeter(Perimeter), write(', perimeter: '), write(Perimeter),
+		color(Color), write(', color: '), write(Color), nl.
+
+:- end_object.
+
+
+% parametric object proxies (with an extra argument to represent identity):
+
+circle('#1', 1.23, blue).
+circle('#2', 3.71, yellow).
+circle('#3', 0.39, green).
+circle('#4', 5.74, black).
+circle('#5', 8.32, cyan).