built-in method

# `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 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 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)

See also

expand_goal/2, goal_expansion/2, term_expansion/2