..
   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
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   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
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.. 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 have
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`
