PDC Prolog

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PDC Prolog runs on IBM PCs (DOS, OS/2, Windows and SCO Unix). Formerly known as Turbo Prolog from Borland. It includes a native code compiler but is incompatible with most other Prologs. Its variables are strongly typed, unlike most other Prologs.


Prolog Development Center is a company that was formed out of an older operation that supplied COMAL systems to educational institutions in the form of UniCOMAL. They developed a version of Prolog for DOS that unlike other such systems was a compiled language rather than an interpreter. This gained some notoriety as a Prolog compiler had been considered something of a practical impossibility. The company had solved this by structuring the language in a similar fashion to Pascal while retaining most other Prolog features, nota bene Comal is a version of Basic with Pascal structural features so it was not a completely new field for PDC.

The system was licenced to Borland that added the IDE and graphical toolkit they had been shipping with their Turbo Pascal product to the system and marketed it as Turbo Prolog.

With version 3.2 released in 1990 the company started to offer a 16-bit OS/2 front end that was completely source code compatible with the DOS front end and indeed if you bought the OS/2 version the DOS system was bundled with it. The 3.2 release also saw a rewritten editor that while similar in appearance to the original Borland one was actually written in PDC Prolog and could therefore be integrated into user programs. It also had some interesting features such as hypertext support and the ability to start other programs which meant it was commonly used as a user interface for OS/2 and DOS programs developed with the system.

Version 3.31 of PDC Prolog was delivered in 1992 and added back ends for Xenix and a couple of other Unix like systems for IBM PC compatibles. An OEM version of the Phar Lap DOS extender was shipped with the system that allowed programmers to generate DOS programs for 286 and 386 systems with extended or expanded memory that allowed significantly bigger heaps than standard DOS and thus allowing larger programs to run without constantly swapping out to disk. It also featured a rudimentary support for GUI programming on MS Windows 3.x and OS/2, much like the text-mode version there was source mode compatibility between the GUI code for the two systems.