Did you know ... | Search Documentation: |
![]() | Pack logtalk -- logtalk-3.81.0/manuals/_sources/refman/methods/goal_expansion_2.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: goal_expansion/2; Built-in method .. _methods_goal_expansion_2:
::
goal_expansion(Goal, ExpandedGoal)
Defines an expansion for a goal. The first argument is the goal to be
expanded. The expanded goal is returned in the second argument. This
predicate is called recursively on the expanded goal until a fixed point
is reached. Thus, care must be taken to avoid compilation loops. This
predicate, when defined and within scope, is automatically called by the
:ref:methods_expand_goal_2
method. Use of this predicate
by the expand_goal/2 method may be restricted by changing its
default public scope.
Goal expansion may be also be applied when compiling source files by
defining the object providing access to the goal_expansion/2 clauses
as a :term:`hook object`. Clauses for the
goal_expansion/2 predicate defined within an object or a category
are never used in the compilation of the object or the category
itself. Moreover, in this context, goals wrapped using the
:ref:control_external_call_1
compiler bypass control
construct are not expanded and any expanded goal wrapped in this control
construct will not be further expanded.
Objects and categories implementing this predicate should declare that they implement the :ref:`expanding apis:expanding/0` built-in protocol if no ancestor already declares it. This protocol implementation relation can be declared as either :ref:`protected or private <inheritance_scope>` to restrict the scope of this predicate.
::
goal_expansion(+callable, -callable)
- zero_or_one
(none)
::
goal_expansion(write(Term), (write_term(Term, []), nl))
.
goal_expansion(read(Term), (write('Input: '), {read(Term)}))
.
.. seealso::
:ref:methods_expand_goal_2
,
:ref:methods_expand_term_2
,
:ref:methods_term_expansion_2
,
:ref:predicates_logtalk_load_context_2