Logtalk

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.

Features

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).

Examples

Logtalk's syntax is based on Prolog:

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

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
true.

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

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]

Applications

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

• Mercury (programming language)
• Oz (programming language)
• Prolog++
• Visual Prolog

References

External links

• Official website
• Logtalking blog
• From Plain Prolog to Logtalk Objects: Effective Code Encapsulation and Reuse (Invited Talk). Paulo Moura. Proceedings of the 25th International Conference on Logic Programming (ICLP), July 2009. LNCS 5649. Springer-Verlag Berlin Heidelberg". (Slides)