.. This file is part of Logtalk https://logtalk.org/ SPDX-FileCopyrightText: 1998-2024 Paulo Moura <pmoura@logtalk.org> SPDX-License-Identifier: Apache-2.0

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: current_predicate/1; Built-in method .. _methods_current_predicate_1:

current_predicate/1

Description

::

current_predicate(Predicate)

Enumerates, by backtracking, visible, user-defined, object predicates. Built-in predicates and predicates not declared using a scope directive are not enumerated.

This predicate also succeeds for any predicates listed in :ref:directives_uses_2 and :ref:directives_use_module_2 directives.

When Predicate is bound at compile-time to a (:)/2 term, this predicate enumerates module predicates (assuming that the :term:`backend Prolog compiler` supports modules).

Modes and number of proofs

::

current_predicate(?predicate_indicator) - zero_or_more

Errors

| Predicate is neither a variable nor a valid predicate indicator: | type_error(predicate_indicator, Predicate) | Predicate is a Name/Arity term but Functor is neither a variable nor an atom: | type_error(atom, Name) | Predicate is a Name/Arity term but Arity is neither a variable nor an integer: | type_error(integer, Arity) | Predicate is a Name/Arity term but Arity is a negative integer: | domain_error(not_less_than_zero, Arity)

Examples

| To enumerate, by backtracking, the locally visible user predicates or the user predicates visible in :term:this: | current_predicate(Predicate) | To enumerate, by backtracking, the public and protected user predicates visible in :term:self: | ::current_predicate(Predicate) | To enumerate, by backtracking, the public user predicates visible for an explicit object: | Object::current_predicate(Predicate)

An example of enumerating locally visible object predicates. These include predicates listed using :ref:directives_uses_2 and :ref:directives_use_module_2 directives:

::

:- object(foo).

:- uses(bar, [
    baz/1, quux/2
]).

:- public(pred/1).
pred(X) :-
   current_predicate(X).

:- end_object.

::

| ?- foo::pred(X). X = pred/1 ; X = baz/1 ; X = quux/2 ; no

.. seealso::

:ref:methods_current_op_3, :ref:methods_predicate_property_2, :ref:directives_uses_2, :ref:directives_use_module_2