..
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   SPDX-FileCopyrightText: 1998-2025 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
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.. _faq_general:

General
=======

* :ref:`faq_general_versions`
* :ref:`faq_general_prolog`
* :ref:`faq_general_modules`
* :ref:`faq_general_expansion`

.. _faq_general_versions:

Why are all versions of Logtalk numbered 2.x or 3.x?
----------------------------------------------------

The numbers "2" and "3" in the Logtalk version string refer to,
respectively, the second and the third generations of the Logtalk
language. Development of Logtalk 2 started in January 1998, with the
first alpha release for registered users in July and the first public
beta on October. The first stable version of Logtalk 2 was released
in February 9, 1999. Development of Logtalk 3 started in April 2012,
with the first public alpha released in August 21, 2012. The first
stable version of Logtalk 3 was released in January 7, 2015.

.. _faq_general_prolog:

Why do I need a Prolog compiler to use Logtalk?
-----------------------------------------------

Currently, the Logtalk language is implemented as a *trans-compiler*
to Prolog instead of as a standalone compiler. Compilation of Logtalk
source files is performed in two steps. First, the Logtalk compiler
converts a source file to a Prolog file. Second, the chosen Prolog
compiler is called by Logtalk to compile the intermediate Prolog file
generated on the first step. The implementation of Logtalk as a
trans-compiler allows users to use Logtalk together with features only
available on specific Prolog compilers.

.. _faq_general_modules:

Is the Logtalk implementation based on Prolog modules?
------------------------------------------------------

No. Logtalk is (currently) implemented in plain Prolog code. Only a
few Prolog compilers include a module system, with several
compatibility problems between them. Moreover, the current ISO Prolog
standard for modules is next to worthless and is ignored by most of
the Prolog community. Nevertheless, the Logtalk compiler is able to
compile simple modules (using a common subset of module directives)
as objects for backward-compatibility with existing code (see the
:ref:`migration_migration` for details).

.. _faq_general_expansion:

Does the Logtalk implementation use term-expansion?
---------------------------------------------------

No. Term-expansion mechanisms are not standard and are not available
in all supported Prolog compilers.
