Include Paulo Moura's Logtalk OO LP system

git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@53 b08c6af1-5177-4d33-ba66-4b1c6b8b522a

Logtalk/examples/roots/abstract_class.lgt

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+
+:- object(abstract_class,
+	implements(abstract_classp),
+	instantiates(class),
+	specializes(object)).
+
+
+	:- info([
+		version is 2,
+		authors is 'Paulo Moura',
+		date is 2000/7/24,
+		comment is 'Default metaclass for all abstract classes.']).
+
+
+	metaclass :-
+		self(Self),
+		instantiates_class(Class, Self),
+		this(This),
+		Class::ancestor(This).
+
+
+	abstract_class :-
+		self(Self),
+		Self \= abstract_class.
+
+
+	strict_instance :-
+		fail.
+
+
+:- end_object.