..
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   SPDX-FileCopyrightText: 1998-2024 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.
   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
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   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
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.. rst-class:: align-right

**built-in method**

.. index:: pair: existence_error/2; Built-in method
.. _methods_existence_error_2:

``existence_error/2``
=====================

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

::

   existence_error(Thing, Culprit)

Throws an existence error. Used when the subject of an operation does not
exist. This built-in method is declared private and thus cannot be used as a
message to an object. Calling this predicate is equivalent to the following
sequence of goals:

::

   ...,
   context(Context),
   throw(error(existence_error(Thing,Culprit), Context)).

This allows the user to generate errors in the same format used by the
runtime.

Possible values for ``Thing`` include:

- ``predicate_declaration``
- ``procedure``
- ``source_sink``
- ``stream``
- ``object``
- ``protocol``
- ``category``
- ``module``
- ``library``
- ``file``
- ``goal_thread``

The value of ``Culprit`` is the argument or one of its sub-terms that caused
the error.

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

::

   existence_error(@nonvar, @nonvar) - error

Errors
------

| When called:
|     ``existence_error(Thing, Culprit)``

Examples
--------

::

   ...,
   \+ current_object(payroll),
   existence_error(object, payroll).

.. seealso::

   :ref:`methods_catch_3`,
   :ref:`methods_throw_1`,
   :ref:`methods_context_1`,
   :ref:`methods_instantiation_error_0`,
   :ref:`methods_uninstantiation_error_1`,
   :ref:`methods_type_error_2`,
   :ref:`methods_domain_error_2`,
   :ref:`methods_evaluation_error_1`,
   :ref:`methods_permission_error_3`,
   :ref:`methods_representation_error_1`,
   :ref:`methods_resource_error_1`,
   :ref:`methods_syntax_error_1`,
   :ref:`methods_system_error_0`
