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   Copyright 1998-2019 Paulo Moura <pmoura@logtalk.org>

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   you may not use this file except in compliance with the License.
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.. index:: pair: predicate_property/2; Built-in method
.. _methods_predicate_property_2:

predicate_property/2
====================

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

::

   predicate_property(Predicate, Property)

Enumerates, by backtracking, the properties of a visible object predicate.
Properties for predicates not declared using a scope directive are not
enumerated. The valid predicate properties are listed in the language
grammar section on :ref:`predicate properties <grammar_predicate_properties>`
and described in the User Manual section on
:ref:`predicate properties <predicates_properties>`.

When ``Predicate`` is ground at compile time and its predicate indicator
is listed in a :ref:`directives_uses_2` or :ref:`directives_use_module_2`
directive, properties are enumerated for the referenced object or module
predicate.

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

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

::

   predicate_property(+callable, ?predicate_property) - zero_or_more

Errors
------

| Predicate is a variable:
|     ``instantiation_error``
| Predicate is neither a variable nor a callable term:
|     ``type_error(callable, Predicate)``
| Property is neither a variable nor a valid predicate property:
|     ``domain_error(predicate_property, Property)``

Examples
--------

| To enumerate, by backtracking, the properties of a locally visible user predicate or a user predicate visible in :term:`this`:
|     ``predicate_property(Predicate, Property)``
| To enumerate, by backtracking, the properties of a public or protected predicate visible in :term:`self`:
|     ``::predicate_property(Predicate, Property)``
| To enumerate, by backtracking, the properties of a public predicate visible in an explicit object:
|     ``Object::predicate_property(Predicate, Property)``

.. seealso::

   :ref:`methods_current_op_3`,
   :ref:`methods_current_predicate_1`,
   :ref:`directives_uses_2`,
   :ref:`directives_use_module_2`
