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.. rst-class:: align-right

built-in method

.. index:: pair: expand_term/2; Built-in method .. _methods_expand_term_2:

expand_term/2

Description

::

expand_term(Term, Expansion)

Expands a term. The most common use is to expand a grammar rule into a clause. Users may override the default Logtalk grammar rule translator by defining clauses for the :ref:methods_term_expansion_2 hook predicate.

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 term_expansion/2 hook predicate within scope, then this predicate is called to provide an expansion that is then unified with the second argument; if the term_expansion/2 predicate is not used and the first argument is a compound term with functor (-->)/2 then the default Logtalk grammar rule translator is used, with the resulting clause being unified with the second argument; when the translator is not used, the two arguments are unified. The expand_term/2 predicate may return a single term or a list of terms.

This built-in method may be used to expand a grammar rule into a clause for use with the built-in database methods.

Automatic term expansion is only performed at compile time (to expand terms read from a source file) when using a :term:`hook object`. This predicate can be used by the user to manually perform term expansion at runtime (for example, to convert a grammar rule into a clause).

Modes and number of proofs

::

expand_term(?term, ?term) - one

Errors

(none)

Examples

(none)

.. seealso::

:ref:methods_expand_goal_2, :ref:methods_goal_expansion_2, :ref:methods_term_expansion_2