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This file is part of Logtalk
Copyright 1998-2023 Paulo Moura
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

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.


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Logtalk is a declarative object-oriented logic programming language that extends and leverages the Prolog language with a feature set suitable for programming in the large. Logtalk supports modern code encapsulation and code reuse mechanisms while preserving the declarative programming features of Prolog.

Logtalk is implemented as a trans-compiler in highly portable code and can use most modern and standards compliant Prolog implementations as a backend compiler.

As a multi-paradigm language, Logtalk includes support for both prototypes and classes, protocols (interfaces), categories (components and hot-patching), event-driven programming, coinduction, lambda expressions, and high-level multi-threading programming. Logtalk uses standard Prolog syntax with the addition of some operators and directives for a smooth learning path.

Logtalk is distributed under a commercial friendly license and includes full documentation, tutorials, portable libraries, a comprehensive set of portable developer tools, and numerous programming examples to help get you started.

Logtalk development adheres to the Contributor Covenant code of conduct. By participating, you are expected to uphold this code. Please report unacceptable behavior to

Logtalk website

The latest stable release of the Logtalk is always available at:

At this address you can download installers for your operating-system and find full documentation on Logtalk.


Logtalk can be installed either from sources by running a couple of shell scripts or by using an installer for your operating system. For manual installation, see the file for detailed instructions.

The file contains descriptions of all Logtalk updates since the first public version. Please check it if you are upgrading from a previous Logtalk version.

If you are upgrading from the previous Logtalk 2.x generation, please check the file for instructions on how to upgrade your programs or your custom adapter files to run under Logtalk 3.x.


The file provides detailed instructions for customizing the Logtalk installation and working environment.


The file provides quick instructions for those of you in a hurry to run Logtalk, provided that your favorite Prolog compiler is supported and installed.


A quick and highly recommended introduction for users comfortable with Prolog and with general knowledge about object-oriented programming is available at the Learn X in Y minutes website.

The HTML version of the Logtalk Handbook is included with the sources and can be found in the manuals directory. It's also available online at:

PDF, ePub, and Texinfo versions of the Logtalk Handbook can be downloaded from:

The Handbook is the entry point for the Logtalk documentation. It includes the user manual, the reference manual, glossary, FAQ, the library overviews, plus the developer tools documentation.

The API documentation for the core, library, tools, and contributions is provided in HTML format and can be found in the docs directory and also available online at:

Most directories include documentation files.

On POSIX systems, there's also a man page for most shell scripts. A list of these scripts can be generated using the apropos logtalk command. HTML versions of the man pages are also available at the Logtalk website.


To register as a Logtalk user please use the registration form at:

Registration is optional. But it's also a way of showing your support and an opportunity for us to learn about the cool projects where you will be using Logtalk.


Support channels include:

For more information on support options, please consult:


If you find Logtalk useful, please include a citation on your publications (also cite the used backend Prolog compilers). The BIBLIOGRAPHY.bib file includes bibliographic references in BibTeX format (including the 2003 PhD thesis on Logtalk design and implementation and the Logtalk Handbook). See also the CITATION.cff file.


Contributions are most welcome! See the file for details.


Logtalk is copyrighted by Paulo Moura and made available under the Apache License 2.0. See the LICENSE.txt file for the license terms. The copyright notice and license applies to all files in this release unless otherwise explicitly stated. See the NOTICE.txt for additional copyright information.

Some files that are part of the Logtalk distribution are distributed using a different license and/or are copyrighted by a Logtalk contributor.

Some examples are adaptations to Logtalk of Prolog examples found elsewhere (e.g. in manuals, tutorials, books, and public discussion forums). See those examples documentation for information on the sources of the original code.

Logtalk is a registered trademark of Paulo Moura.