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/points/point_history.lgt

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+
+:- category(point_history).
+
+
+	:- info([
+		version is 1.0,
+		date is 1998/3/23,
+		authors is 'Paulo Moura',
+		comment is 'Point position history management predicates.',
+		source is 'Example adopted from the SICStus Objects documentation.']).
+
+
+	:- public(add_to_history/1).
+	:- mode(add_to_history(+nonvar), one).
+
+	:- public(init_history/1).
+	:- mode(init_history(+list), one).
+
+	:- public(history/1).
+	:- mode(history(-list), zero_or_one).
+
+	:- public(print_history/0).
+	:- mode(print_history, zero_or_one).
+
+	:- private(history_/1).
+	:- dynamic(history_/1).
+	:- mode(history_(-list), zero_or_one).
+
+
+	add_to_history(Location) :-
+		::retract(history_(History)),
+		::assertz(history_([Location| History])).
+
+
+	init_history(History) :-
+		::retractall(history_(_)),
+		::assertz(history_(History)).
+
+
+	history(History) :-
+		::history_(History).
+
+
+	print_history :-
+		::history_(History),
+		write('location history: '),
+		write(History),
+		nl.
+
+
+:- end_category.