Visual Prolog - Programming language

Visual Prolog is an open source programming language created in 1996.

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Visual Prolog, also formerly 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 Prolog Development Center (PDC) that originally developed it. Visual Prolog can build Microsoft Windows GUI-applications, console applications, DLLs (dynamic link libraries), and CGI-programs. Read more on Wikipedia...

Visual Prolog Wikipedia page
Visual Prolog on HOPL
See also: (3 related languages)Prolog, ISBN, Mercury

Example from Wikipedia:

class hanoi
   predicates
       hanoi : (unsigned N).
end class hanoi
 
implement hanoi
   domains
       pole = string.
 
   clauses
       hanoi(N) :- move(N, "left", "centre", "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, C),
           move(N-1, B, A, C).
end implement hanoi
 
goal
   console::init(),
   hanoi::hanoi(4).