..
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   Copyright 1998-2022 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.
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       http://www.apache.org/licenses/LICENSE-2.0

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.. rst-class:: align-right

**directive**

.. index:: pair: mode/2; Directive
.. _directives_mode_2:

``mode/2``
==========

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

::

   mode(Mode, NumberOfProofs)

Most predicates can be used with several instantiations modes. This
directive enables the specification of each
:ref:`instantiation mode <predicates_mode_instantiation>` and the
corresponding :ref:`number of proofs <predicates_mode_number_of_proofs>`
(not necessarily distinct solutions). You may also use this directive
for documenting grammar rule non-terminals.

Template and modes
------------------

::

   mode(+predicate_mode_term, +number_of_proofs)
   mode(+non_terminal_mode_term, +number_of_proofs)

Examples
--------

::

   :- mode(atom_concat(-atom, -atom, +atom), one_or_more).
   :- mode(atom_concat(+atom, +atom, -atom), one).

   :- mode(var(@term), zero_or_one).

   :- mode(solve(+callable, -list(atom)), zero_or_one).

.. seealso::

   :ref:`directives_info_2`,
   :ref:`methods_predicate_property_2`
