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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 (by default, it will generate a number of % warnings, which are expected):

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

% attic/0 is a public predicate, defined to be true:

| ?- house::attic. yes

% cellar/0 is also a public predicate but without a definition; the message will fail per closed world assumption:

| ?- house::cellar. no

% no pool/0 predicate declared; closed world assumption doesn't apply % and thus the message generates an error:

| ?- house::pool. ERROR: error(existence_error(predicate_declaration,pool/0), logtalk(house::pool, _))

% our house is pleasant as we have a porch and a garden:

| ?- house::pleasant. yes

% but our house is not practical as we don't have a shed for the garden % tools or a garage to protect our bikes (per closed world assumption, % calling declared by undefined predicates fail):

| ?- house::practical. no

% no idea if we live in a fun house, however, as calling a undeclared and % undefined predicate generates an error; the closed world assumption % doesn't apply in this case:

| ?- house::fun. ERROR: error(existence_error(procedure,pool/0), logtalk(house::fun, _))