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The Visual Programming Interface (VPI)

One of the secrets of the power and ease of programming in Visual Prolog is the Visual Programming Interface or the VPI layer. The VPI layer is the foundation for GUI programming, and it has been specially designed as a programming interface for Prolog. The VPI is currently supported on the Windows, NT and OS/2 platforms.

The VPI layer makes it possible to create portable programs; all major parts of GUI applications like Window handling, Controls, Menus, Mouse etc. are portable. The VPI layer is an abstraction of the facilities found in the native GUI API's, it does not try to emulate a single GUI as seen in some portable GUI toolkits.

However since people who are interested in just one platform wants all the facilities on that platform, the VPI also tries to support all facilities on all platforms, meaning that some features if chosen will not be portable - it is entirely up to the programmer to decide whether or not to take advantage of these extra facilities.

See some examples:

The Visual Prolog VDE is implemented in the VPI.
The Visual Prolog debugger is implemented in the VPI.
Label expert.
See many other examples of VPI applications.