Logtalk reference manual
Predicate directive: meta_non_terminal/1
Contents > Reference Manual > Directives > meta_non_terminal/1

## meta_non_terminal/1

#### Description

    meta_non_terminal(MetaNonTerminalTemplate)
    meta_non_terminal((MetaNonTerminalTemplate1, MetaNonTerminalTemplate2, ...))
    meta_non_terminal([MetaNonTerminalTemplate1, MetaNonTerminalTemplate2, ...])

    meta_non_terminal(Entity::MetaNonTerminalTemplate)
    meta_non_terminal((Entity1::MetaNonTerminalTemplate1, Entity2::MetaNonTerminalTemplate2, ...))
    meta_non_terminal([Entity1::MetaNonTerminalTemplate1, Entity2::MetaNonTerminalTemplate2, ...])

    meta_non_terminal(Module:MetaNonTerminalTemplate)
    meta_non_terminal((Module1:MetaNonTerminalTemplate1, Module2:MetaNonTerminalTemplate2, ...))
    meta_non_terminal([Module1:MetaNonTerminalTemplate1, Module2:MetaNonTerminalTemplate2, ...])

Declares meta-non-terminals, i.e., non-terminals that have arguments that will be called as non-terminals (or grammar rule bodies). An argument may also be a closure instead of a goal if the non-terminal uses the `call//1-N` Logtalk built-in methods to construct and call the actual non-terminal from the closure and the additional arguments.

Meta-arguments which are non-terminals are represented by the integer `0`. Meta-arguments which are closures are represented by a positive integer, `N`, representing the number of additional arguments that will be appended to the closure in order to construct the corresponding meta-call. Normal arguments are represented by the atom `*`. Meta-arguments are always called in the meta-non-terminal calling context, not in the meta-non-terminal definition context.

Logtalk allows the use of this directive to override the original meta-non-terminal directive. This is sometimes necessary when calling Prolog module meta-non-terminals due to the lack of standardization of the syntax of the meta-non-terminal templates.

#### Template and modes

    meta_non_terminal(+meta_non_terminal_template_term)

    meta_non_terminal(+object_identifier::+meta_non_terminal_template_term)
    meta_non_terminal(+category_identifier::+meta_non_terminal_template_term)

    meta_non_terminal(+module_identifier:+meta_non_terminal_template_term)

#### Examples

    :- meta_non_terminal(findall(*, 0, *)).

    :- meta_non_terminal(forall(0, 0)).

    :- meta_non_terminal(maplist(2, *, *)).