..
   This file is part of Logtalk <https://logtalk.org/>  
   Copyright 1998-2019 Paulo Moura <pmoura@logtalk.org>

   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,
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.. index:: pair: threaded_engine_next_reified/2; Built-in predicate
.. _predicates_threaded_engine_next_reified_2:

threaded_engine_next_reified/2
==============================

Description
-----------

::

   threaded_engine_next_reified(Engine, Answer)

Retrieves an answer from an engine and signals it to start computing the
next answer. This predicate always succeeds and blocks until an answer
becomes available. Answers are returned using the terms ``the(Answer)``,
``no``, and ``exception(Error)``.

Modes and number of proofs
--------------------------

::

   threaded_engine_next_reified(@nonvar, ?nonvar) - one

Errors
------

| Engine is a variable:
|     ``instantiation_error``
| Engine is neither a variable nor the name of an existing engine:
|     ``existence_error(engine, Engine)``

Examples
--------

::

   % get the next reified answer from the worker_1 engine:
   | ?- threaded_engine_next_reified(worker_1, Answer).

.. seealso::

   :ref:`predicates_threaded_engine_create_3`,
   :ref:`predicates_threaded_engine_next_2`,
   :ref:`predicates_threaded_engine_yield_1`
