Paradigm Logic programming
Designed by Paulo Moura
First appeared 1998 (1998)
Stable release
3.01.0 / September 12, 2015 (2015-09-12)
Preview release
3.00.0 Release Candidate 9 / December 19, 2014 (2014-12-19)
OS Cross-platform
License Artistic License 2.0 (2.x) / Apache License 2.0 (3.01.x)
Website logtalk.org
Influenced by
Prolog, Smalltalk, Objective-C; logic programming, object-oriented programming, prototype-based programming

Logtalk is an object-oriented logic programming language that extends and leverages the Prolog language with a feature set suitable for programming in the large.[1] It provides support for encapsulation and data hiding, separation of concerns and enhanced code reuse.[1] Logtalk uses standard Prolog syntax with the addition of a few operators and directives.

The Logtalk language implementation is distributed under an open source license and can run using a Prolog implementation (compliant with official and de facto standards) as the back-end compiler.


Logtalk aims to bring together the advantages of object-oriented programming and logic programming.[1] Object-orientation emphasizes developing discrete, reusable units of software, while logic programming emphasizes representing the knowledge of each object in a declarative way.

As an object-oriented programming language, Logtalk's major features include support for both classes (with optional metaclasses) and prototypes, parametric objects,[2] protocols (interfaces), categories (components, aspects, hot patching), multiple inheritance, public/protected/private inheritance, event-driven programming, high-level multi-threading programming,[3] reflection, and automatic generation of documentation.

For Prolog programmers, Logtalk provides wide portability, featuring predicate namespaces (supporting both static and dynamic objects), public/protected/private object predicates, coinductive predicates, separation between interface and implementation, simple and intuitive meta-predicate semantics, lambda expressions, definite clause grammars, term-expansion mechanism, and conditional compilation. It also provides a module system based on de facto standard core module functionality (internally, modules are compiled as prototypes).


Logtalk's syntax is based on Prolog:

?- write('Hello world'), nl.
Hello world

Defining an object:

:- object(my_first_object).

    :- initialization((write('Hello world'), nl)).

    :- public(p1/0).
    p1 :- write('This is a public predicate'), nl.

    :- private(p2/0).
    p2 :- write('This is a private predicate'), nl.

:- end_object.

Using the object, assuming is saved in a my_first_object.lgt file:

?- logtalk_load(my_first_object).
Hello world

?- my_first_object::p1.
This is a public predicate

Trying to access the private predicate gives an error:

?- my_first_object::p2.
ERROR: error(permission_error(access, private_predicate, p2), my_first_object::p2, user)

Prolog back-end compatibility

As of October 2011, supported back-end Prolog compilers include B-Prolog, CxProlog, ECLiPSe, GNU Prolog, LeanProlog, Qu-Prolog, SICStus Prolog, SWI-Prolog, XSB, and YAP Prolog.[4] Logtalk allows seamless use of most back-end Prolog compiler libraries from within object and categories.

Developer tools

Logtalk features on-line help, a documenting tool (that can generate PDF and HTML files), an entity diagram generator tool, a built-in debugger (based on an extended version of the traditional Procedure Box model found on most Prolog compilers), a unit test framework with code coverage analysis, and is also compatible with selected back-end Prolog profilers and graphical tracers.[5]


Logtalk has been used to process STEP data models used to exchange product manufacturing information.[6] It has also been used to implement a reasoning system that allows preference reasoning and constraint solving.[7]

See also


  1. 1 2 3 Paulo Moura (2003). Logtalk: Design of an Object-Oriented Logic Programming Language. PhD thesis. Universidade da Beira Interior
  2. Moura, Paulo (2011). Programming Patterns for Logtalk Parametric Objects. Applications of Declarative Programming and Knowledge Management. Lecture Notes in Computer Science. 6547. doi:10.1007/978-3-642-20589-7_4. ISBN 978-3-642-20588-0.
  3. "Practical Aspects of Declarative Languages". Lecture Notes in Computer Science. 4902. 2008. doi:10.1007/978-3-540-77442-6. ISBN 978-3-540-77441-9.
  4. "Logtalk compatibility". Logtalk.org. 2013-02-10. Retrieved 2013-08-19.
  5. / (2013-02-12). "Developer Tools 路 LogtalkDotOrg/logtalk3 Wiki 路 GitHub". Github.com. Retrieved 2013-08-19.
  6. "Logic Programming". Lecture Notes in Computer Science. 4079. 2006. doi:10.1007/11799573. ISBN 978-3-540-36635-5.
  7. Victor Noël; Antonis Kakas (2009). Gorgias-C: Extending Argumentation with Constraint Solving (PDF). Logic Programming and Nonmonotonic Reasoning. Lecture Notes in Computer Science. 5753. pp. 535–541.
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