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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: term_expansion/2; Built-in method .. _methods_term_expansion_2:

term_expansion/2

Description

::

term_expansion(Term, Expansion)

Defines an expansion for a term. This predicate, when defined and within scope, is automatically called by the :ref:methods_expand_term_2 method. When that is not the case, the expand_term/2 method only uses the default expansions. Use of this predicate by the expand_term/2 method may be restricted by changing its default public scope.

The term_expansion/2 predicate may return a list of terms. Returning an empty list effectively suppresses the term.

Term expansion may be also be applied when compiling source files by defining the object providing access to the term_expansion/2 clauses as a :term:`hook object`. Clauses for the term_expansion/2 predicate defined within an object or a category are never used in the compilation of the object or the category itself. Moreover, in this context, terms wrapped using the :ref:control_external_call_1 compiler bypass control construct are not expanded and any expanded term wrapped in this control construct will not be further expanded.

Objects and categories implementing this predicate should declare that they implement the :ref:`expanding apis:expanding/0` protocol if no ancestor already declares it. This protocol implementation relation can be declared as either :ref:`protected or private <inheritance_scope>` to restrict the scope of this predicate.

Modes and number of proofs

::

term_expansion(+nonvar, -nonvar) - zero_or_one term_expansion(+nonvar, -list(nonvar)) - zero_or_one

Errors

(none)

Examples

::

term_expansion((:- license(default)), (:- license(gplv3))). term_expansion(data(Millimeters), data(Meters)) :- Meters is Millimeters / 1000.

.. seealso::

:ref:methods_expand_goal_2, :ref:methods_expand_term_2, :ref:methods_goal_expansion_2, :ref:predicates_logtalk_load_context_2