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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

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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