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   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.
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.. rst-class:: align-right

**built-in method**

.. index:: pair: expand_goal/2; Built-in method
.. _methods_expand_goal_2:

``expand_goal/2``
=================

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

::

   expand_goal(Goal, ExpandedGoal)

Expands a goal. The expansion works as follows: if the first argument
is a variable, then it is unified with the second argument; if the first
argument is not a variable and there are local or inherited clauses for
the ``goal_expansion/2`` hook predicate within scope, then this predicate
is recursively called until a fixed-point is reached to provide an
expansion that is then unified with the second argument; if the
``goal_expansion/2`` predicate is not within scope, the two arguments
are unified.

Automatic goal expansion is only performed at compile-time (to expand
the body of clauses and meta-directives read from a source file) when
using :term:`hook objects <hook object>`. This predicate can be
used by the user to manually perform goal expansion at runtime (for
example, before asserting a clause).

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

::

   expand_goal(?term, ?term) - one

Errors
------

(none)

Examples
--------

(none)

.. seealso::

   :ref:`methods_expand_term_2`,
   :ref:`methods_goal_expansion_2`,
   :ref:`methods_term_expansion_2`
