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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(questions(loader)). ...

% we can now ask the ultimate question:

| ?- logtalk::ask_question(question, hitchhikers, ultimate_question, '=='(42), N).

The answer to the ultimate question of Life, The Universe and Everything is? > 42.

N = 42 yes

% note that the fourth argument of the logtalk::ask_question/5 predicate is % a closure that is used to type-check the answer:

| ?- logtalk::ask_question(question, hitchhikers, ultimate_question, '=='(42), N).

The answer to the ultimate question of Life, The Universe and Everything is? > icecream. > tea. > 42.

N = 42 yes

% if running using JIProlog, SWI-Prolog, or YAP as the backend, asking the % question again after the goal will present a GUI dialog:

| ?- logtalk_load(questions(loader_gui)). ...

| ?- logtalk::ask_question(question, hitchhikers, ultimate_question, '=='(42), N). ...