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This file is part of Logtalk https://logtalk.org/ SPDX-FileCopyrightText: 1998-2023 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.

% start by loading the example:

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

% we can always send a message for a public predicate:

| ?- prototype::foo(Foo).

Foo = 1 yes

% but we cannot send messages for protected or private predicates:

| ?- prototype::bar(_).

error(permission_error(access,protected_predicate,bar/1),logtalk(prototype::bar(_),c(user,user,r(user,prototype,[],[]))))

| ?- prototype::baz(_).

uncaught exception: error(permission_error(access,private_predicate,baz/1),logtalk(prototype::baz(_),c(user,user,r(user,prototype,[],[]))))

% same for local predicates not declared by a scope directive; note the % different exception term compared with the two previous queries:

| ?- prototype::local(_).

error(existence_error(predicate_declaration,local/1),logtalk(prototype::local(_),c(user,user,r(user,prototype,[],[]))))

% from the object holding the scope directives, we can always access any % predicate redefinition in the descendants (note that the p_foo/1, p_bar/1, % and p_baz/1 predicates are declared public, defined in the "prototype" % object, and inherited by the "descendant" object):

| ?- descendant::p_foo(Foo).

Foo = 2 yes

| ?- descendant::p_bar(Bar).

Bar = 2 yes

| ?- descendant::p_baz(Baz).

Baz = 2 yes

% from descendant objects, we can access inherited predicate definitions for % public and protected predicates:

| ?- descendant::d_foo(Foo).

Foo = 1 yes

| ?- descendant::d_bar(Bar).

Bar = 1 yes