Logtalk 2.12.0 files.

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Logtalk/examples/dynpred/NOTES

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+=================================================================
+Logtalk - Object oriented extension to Prolog
+Release 2.12.0
+
+Copyright (c) 1998-2002 Paulo Moura.  All Rights Reserved.
+=================================================================
+
+
+To load all entities in this example consult the dynpred.loader 
+utility file (note that this is a Prolog file).
+
+This folder contains examples of using some of the built-in database  
+handling methods.

Logtalk/examples/dynpred/SCRIPT

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+=================================================================
+Logtalk - Object oriented extension to Prolog
+Release 2.12.0
+
+Copyright (c) 1998-2002 Paulo Moura.  All Rights Reserved.
+=================================================================
+
+
+% Sending to descendant the message p/1, returns the definition in root:
+
+| ?- descendant::p(Value).
+
+Value = root
+yes
+
+
+% Asserting a local definition for p/1 in descendant overrides the inherited 
+% definition:
+
+| ?- descendant::(assertz(p(descendant)), p(Value)).
+
+Value = descendant
+yes
+
+
+% If we retract the local definition, again the inherited definition form root
+% will be used:
+
+| ?- descendant::(retractall(p(_)), p(Value)).
+
+Value = root
+yes
+
+
+% class does not understand the message p1/1 (the predicate is declared only 
+% for the class descendant instances):
+
+| ?- class::p1(X).
+
+error(existence_error(predicate_declaration, p1(_)), class::p1(_), user)
+
+
+% the same message is valid for the class instances:
+
+| ?- instance::p1(X).
+
+X = class
+yes
+
+
+% If we assert a clause for a new predicate, p2/1, in the class
+% (a side-effect being a dynamic declaration of the predicate):
+
+| ?- class::assertz(p2(class)).
+
+yes
+
+
+% the new predicate, like p1/1, is not available for the class:
+
+| ?- class::p2(Value).
+
+error(existence_error(predicate_declaration, p2(_)), class::p2(_), user)
+
+
+% but is available for the class instances, the same way as p1/1:
+
+| ?- instance::p2(X).
+
+X = class
+yes
+
+
+% Using a prototype, assert three new predicates (the method object_assert/0 
+% asserts the predicate public_predicate/0 from outside the prototype; the 
+% method self_assert/0 asserts the predicate protected_predicate/0 in self; 
+% the method this_assert/0 asserts the predicate private_predicate/0 in this):
+
+| ?- prototype::(object_assert, self_assert, this_assert).
+
+yes
+
+
+% and check the resulting scope of each predicate:
+
+| ?- prototype::dynamic_predicates.
+
+public_predicate/0 - public
+protected_predicate/0 - protected
+private_predicate/0 - private
+yes

Logtalk/examples/dynpred/class.lgt

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+
+:- object(class,
+	instantiates(metaclass)).
+
+
+	:- public(p1/1).
+
+
+	p1(class).
+
+
+:- end_object.

Logtalk/examples/dynpred/descendant.lgt

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+
+:- object(descendant,
+    extends(root)).
+
+
+:- end_object.

Logtalk/examples/dynpred/dynpred.loader

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+
+:- initialization(
+	logtalk_load([
+		root,
+		descendant,
+		metaclass,
+		class,
+		instance,
+		prototype])).

Logtalk/examples/dynpred/instance.lgt

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+
:- object(instance,
	instantiates(class)).


:- end_object.

Logtalk/examples/dynpred/metaclass.lgt

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+
+:- object(metaclass,
+	instantiates(metaclass)).
+
+
+:- end_object.

Logtalk/examples/dynpred/prototype.lgt

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+
+:- object(prototype).
+
+
+	:- public(object_assert/0).
+	:- public(self_assert/0).
+	:- public(this_assert/0).
+
+	:- public(dynamic_predicates/0).
+
+
+	object_assert :-
+		self(Self),
+		Self::assertz(public_predicate).
+
+
+	self_assert :-
+		::assertz(protected_predicate).
+
+
+	this_assert :-
+		assertz(private_predicate).
+
+
+	dynamic_predicates :-
+		current_predicate(Functor/Arity),
+		functor(Predicate, Functor, Arity),
+		predicate_property(Predicate, (dynamic)),
+		predicate_property(Predicate, Scope),
+		scope(Scope),
+		writeq(Functor/Arity), write(' - '), writeq(Scope), nl,
+		fail.
+
+	dynamic_predicates.
+
+
+	scope(private).
+	scope(protected).
+	scope((public)).
+
+
+:- end_object.

Logtalk/examples/dynpred/root.lgt

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+
+:- object(root).
+
+
+    :- public(p/1).
+    :- dynamic(p/1).
+
+
+    p(root).
+
+
+:- end_object.