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This file is part of Logtalk <https://logtalk.org/>  
Copyright 1998-2021 Paulo Moura <pmoura@logtalk.org>  
SPDX-License-Identifier: Apache-2.0

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
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% start by loading the example:

| ?- logtalk_load(roles(loader)).
...


% prototypes can declare and defined their own predicates:

| ?- prototype::foo(Foo).

Foo = 1
yes


% derived prototypes inherit predicates from their parents:

| ?- descendant::foo(Foo).

Foo = 2 
yes

| ?- descendant::bar(X, Y).

X = 1,
Y = 2
yes


% a class that is its own metaclass can access its own public predicates
% using message sending:

| ?- superclass::foo(Foo).

Foo = 1
yes


% a class that doesn't have a metaclass cannot receive any message as
% the predicate declaration lookup to answer to validate the message
% would start in the metaclass:

| ?- subclass::current_predicate(_).

no


% an instance can receive messages for predicates declared in its
% class(es) and in its class(es) superclass(es):

| ?- instance::current_predicate(P).

P = bar/2 ;
P = foo/1
yes

| ?- instance::foo(Foo).

Foo = 2
yes

| ?- instance::bar(X, Y).

X = 1,
Y = 2
yes

| ?- empty_instance::foo(Foo).

Foo = 1
yes
