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   SPDX-License-Identifier: Apache-2.0

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   you may not use this file except in compliance with the License.
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.. rst-class:: align-right

**built-in predicate**

.. index:: pair: protocol_property/2; Built-in predicate
.. _predicates_protocol_property_2:

``protocol_property/2``
=======================

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

::

   protocol_property(Protocol, Property)

Enumerates, by backtracking, the properties associated with the currently
defined protocols. The valid properties are listed in the language grammar
section on :ref:`entity properties <grammar_entity_properties>` and described
in the User Manual section on :ref:`protocol properties <protocols_properties>`.

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

::

   protocol_property(?protocol_identifier, ?protocol_property) - zero_or_more

Errors
------

| ``Protocol`` is neither a variable nor a valid protocol identifier:
|     ``type_error(protocol_identifier, Protocol)``
| ``Property`` is neither a variable nor a callable term:
|     ``type_error(callable, Property)``
| ``Property`` is a callable term but not a valid protocol property:
|     ``domain_error(protocol_property, Property)``

Examples
--------

::

   % enumerate the properties of the monitoring built-in protocol:
   | ?- protocol_property(monitoring, Property).

   Property = source_data ;
   Property = static ;
   Property = built_in ;
   ...

.. seealso::

   :ref:`predicates_abolish_protocol_1`,
   :ref:`predicates_create_protocol_3`,
   :ref:`predicates_current_protocol_1`,
   :ref:`predicates_conforms_to_protocol_2_3`,
   :ref:`predicates_extends_protocol_2_3`,
   :ref:`predicates_implements_protocol_2_3`
