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   Copyright 1998-2021 Paulo Moura <pmoura@logtalk.org>
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.. 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 instantiation mode and the
corresponding 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`
