What is XPCE?

XPCE is a toolkit for developing graphical applications in Prolog and other interactive and dynamically typed languages. XPCE follows a rather unique approach to developing GUI applications, which we will try to summarise using the points below.

Add object layer to Prolog

XPCE's kernel is a object-oriented engine that allows for the definition of methods in multiple languages. The built-in graphics are defined in C for speed as well as to define the platform-independent layer. Applications, as well as some application-oriented libraries are defined as XPCE-classes with their methods defined in Prolog.

Prolog-defined methods can receive arguments in native Prolog data, native Prolog data may be associated with XPCE instance-variables and XPCE errors are (selectively) mapped to Prolog exceptions. These features make XPCE a natural extension to your Prolog program.

High level of abstraction

XPCE's graphical layer provides a high abstraction level, hiding details on event-handling, redraw-management and layout management from the application programmer, while still providing access to the primitives to deal with exceptional cases.

Exploit rapid Prolog development cycle

Your XPCE classes are defined in Prolog and the methods run naturally in Prolog. This implies you can easily cross the border between your application and the GUI-code inside the tracer. It also implies you can modify source-code and recompile while your application is running.

Platform independent programs

XPCE/Prolog code is fully platform-independent, making it feasible to develop on your platform of choice and deliver on the platform of choice of your users. As SWI-Prolog saved-states are machine-independent, applications can be delivered as a saved-state. Such states can be executed transparently using the development-environment to facilitate debugging or the runtime emulator for better speed and space-efficiency.

Links about motivation and impressions

• Why using XPCE for graphics in Prolog?
• Why no GUI-Builder?
• Some code fragments to get an impression
• Some screen dumps of applications
• The design of the XPCE/Prolog interface (Publication in Workshop on Logic Programming Environments, 2002)

Documentation

For starters as well as for more experienced users who want to know how particular tasks are tackled using XPCE/Prolog, there is the XPCE UserGuide. The manual is also available a HTML-tar-archive and can be viewed online.

The reference documentation is available using a hypertext system defined in XPCE/Prolog. This tool exploits the XPCE-class descriptions as well as associated hypertext cards to provide various viewpoints and search mechanisms for browsing the reference material. The manual tools are started using the Prolog command manpce/0:

?- manpce.

Finally, the development tools and libraries form a rich set of examples. Just browse through them and then use the Visual Hierarchy Tool to locate the relevant source-code.

On Unix installations, the manpages xpce.1 and xpce-client.1 provide documentation on the command-line options of these commands.