.. 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

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

.. rst-class:: align-right

built-in method

.. index:: pair: (\+)/1; Built-in method .. _methods_not_1:

(\+)/1

Description

::

\+ Goal

Not-provable meta-predicate. True iff call(Goal) is false. This built-in meta-predicate is declared as a private method and thus cannot be used as a message to an object.

.. warning::

The argument is always compiled. As a consequence, when the argument is a control construct (e.g. a conjunction), any meta-variables will be wrapped with the equivalent to the call/1 control construct. Note that these semantics differ from the ISO Prolog Core standard specification for the (\+)/1 built-in predicate.

Meta-predicate template

::

\+ 0

Modes and number of proofs

::

\+ +callable - zero_or_one

Errors

| Goal is a variable: | instantiation_error | Goal is neither a variable nor a callable term: | type_error(callable, Goal)

Examples

| Not-provable goal in the context of the object or category containing the call: | \+ Goal | Not-provable goal sent as a message to :term:self: | \+ ::Goal | Not-provable goal sent as a message to an explicit object: | \+ Object::Goal

.. seealso::

:ref:methods_call_N, :ref:methods_ignore_1, :ref:methods_once_1