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).