Visual Prolog, previously known as PDC Prolog and Turbo Prolog, is a strongly typed object-oriented extension of Prolog. As Turbo Prolog, it was marketed by Borland but it is now developed and marketed by the Danish firm PDC that originally created it. Visual Prolog can build Microsoft Windows GUI-applications, console applications, DLLs (dynamic link libraries), and CGI-programs. It can also link to COM components and to databases by means of ODBC. Visual Prolog contains a compiler which generates x86 machine code. Unlike standard Prolog, programs written in Visual Prolog are statically typed. This allows some errors to be caught at compile-time instead of run-time. History Version 10 introduces object expressions, support for master/slave processes, Microsoft Edge webView2 control and some support for Direct2D+DirectWrite+Windows Imaging Component (see also Visual Prolog 10 New Features). Version 9 introduces bounded polymorphism, extension predicates, threadsafe lock free fact databases, named parameters (see also Visual Prolog 9 New Features). Version 8 introduces presenters, for more user friendly data presentation in debugger and running program (see also Visual Prolog 8 New Features). Version 7.5 contains http server and LALR(1) parser generator (see also Visual Prolog 7.5 New Features). Version 7.4 can generate 64 bit windows code (see also Visual Prolog 7.4 New Features). Version 7.3 introduced generic classes and interfaces (see Generic programming), guarded monitors (see also Visual Prolog 7.3 New Features). Version 7.2 introduced anonymous predicates (a logical pendant to anonymous functions) and namespaces (see also Visual Prolog 7.2 New Features). Version 7.0 introduced parametric polymorphism. Since version 6.0 the language has been fully object-oriented. Hanoi example In the Towers of Hanoi example, the Prolog inference engine figures out how to move a stack of any number of progressively smaller disks, one at a time, from the left pole to the right pole in the described way, by means of a center as transit, so that there's never a bigger disk on top of a smaller disk. The predicate hanoi takes an integer indicating the number of disks as an initial argument. class hanoi predicates hanoi : (unsigned N). end class hanoi implement hanoi domains pole = left; center; right. clauses hanoi(N) :- move(N, left, center, right). class predicates move : (unsigned N, pole A, pole B, pole C). clauses move(0, _, _, _) :- !. move(N, A, B, C) :- move(N-1, A, C, B), stdio::writef("move a disc from % pole to the % pole\n", A,