..
   This file is part of Logtalk <https://logtalk.org/>
   SPDX-FileCopyrightText: 1998-2026 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.


.. rst-class:: align-right

**built-in method**

.. index:: pair: message_hook/4; Built-in method
.. _methods_message_hook_4:

``message_hook/4``
==================

Description
-----------

::

   message_hook(Message, Kind, Component, Tokens)

User-defined hook method for intercepting printing of a message, declared
in the :ref:`logtalk <apis:logtalk/0>` built-in object as a public,
multifile, and dynamic predicate. This hook method is automatically called
by the :ref:`methods_print_message_3` method. When the call
succeeds, the ``print_message/3`` method assumes that the message has
been successfully printed.

Modes and number of proofs
--------------------------

::

   message_hook(@nonvar, @nonvar, @nonvar, @list(nonvar)) - zero_or_one

Errors
------

(none)

Examples
--------

::

   :- multifile(logtalk::message_hook/4).
   :- dynamic(logtalk::message_hook/4).

   % print silent messages instead of discarding them as default
   logtalk::message_hook(_, silent, core, Tokens) :-
       logtalk::message_prefix_stream(silent, core, Prefix, Stream),
       logtalk::print_message_tokens(Stream, Prefix, Tokens).

.. seealso::

   :ref:`methods_message_prefix_stream_4`,
   :ref:`methods_message_tokens_2`,
   :ref:`methods_print_message_3`,
   :ref:`methods_print_message_tokens_3`,
   :ref:`methods_print_message_token_4`,
   :ref:`methods_ask_question_5`,
   :ref:`methods_question_hook_6`,
   :ref:`methods_question_prompt_stream_4`
