# General

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

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

- Is the Logtalk implementation based on Prolog modules?

- Does the Logtalk implementation use term-expansion?

## 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.

## 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.

## 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 Prolog integration and migration for details).

## Does the Logtalk implementation use term-expansion?

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