..
   This file is part of Logtalk <https://logtalk.org/>  
   Copyright 1998-2019 Paulo Moura <pmoura@logtalk.org>

   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,
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.. index:: pair: current_predicate/1; Built-in method
.. _methods_current_predicate_1:

current_predicate/1
===================

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

::

   current_predicate(Predicate)

Enumerates, by backtracking, visible, user-defined, object predicates.
Built-in predicates and predicates not declared using a scope directive
are not enumerated.

When ``Predicate`` is ground at compile time, this predicate also
succeeds for any predicates listed in :ref:`directives_uses_2` and
:ref:`directives_use_module_2` directives.

When ``Predicate`` is bound at compile time to a ``:/2`` term, this
predicate enumerates module predicates (assuming that the
:term:`backend Prolog compiler` supports modules).

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

::

   current_predicate(?predicate_indicator) - zero_or_more

Errors
------

| Predicate is neither a variable nor a valid predicate indicator:
|     ``type_error(predicate_indicator, Predicate)``
| Predicate is a Name/Arity term but Functor is neither a variable nor an atom:
|     ``type_error(atom, Name)``
| Predicate is a Name/Arity term but Arity is neither a variable nor an integer:
|     ``type_error(integer, Arity)``
| Predicate is a Name/Arity term but Arity is a negative integer:
|     ``domain_error(not_less_than_zero, Arity)``

Examples
--------

| To enumerate, by backtracking, the locally visible user predicates or the user predicates visible in :term:`this`:
|     ``current_predicate(Predicate)``
| To enumerate, by backtracking, the public and protected user predicates visible in :term:`self`:
|     ``::current_predicate(Predicate)``
| To enumerate, by backtracking, the public user predicates visible for an explicit object:
|     ``Object::current_predicate(Predicate)``

.. seealso::

   :ref:`methods_current_op_3`,
   :ref:`methods_predicate_property_2`,
   :ref:`directives_uses_2`,
   :ref:`directives_use_module_2`
