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![]() | Pack logtalk -- logtalk-3.81.0/manuals/_sources/refman/methods/context_1.rst.txt |
.. 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: context/1; Built-in method .. _methods_context_1:
::
context(Context)
Returns the execution context for a predicate clause using the term
logtalk(Head,ExecutionContext)
where Head
is the head of the
clause containing the call. This private predicate is mainly used for
providing an error context when type-checking predicate arguments. The
ExecutionContext
term should be regarded as an opaque term, which
can be decoded using the
:ref:`logtalk::execution_context/7 apis:logtalk/0::execution_context/7`
predicate. Calls to this predicate are inlined at compilation time.
.. warning::
As the execution context term includes the clause head, the head
of the clause calling the context(Context)
method cannot contain
the Context
variable as that would result in the creation of
a cyclic term. The compiler detects and reports any offending
clauses by throwing a representation_error(cyclic_term)
error.
::
context(--callable) - one
(none)
::
foo(A, N)
:-
% type-check arguments
context(Context)
,
type::check(atom, A, Context)
,
type::check(integer, N, Context)
,
% arguments are fine; go ahead
... .
.. seealso::
:ref:methods_parameter_2
,
:ref:methods_self_1
,
:ref:methods_sender_1
,
:ref:methods_this_1