Fibonacci numbers in Prolog

Example for versions Visual Prolog 7.2

Create a new project with UI Strategy “Console” and replace contents of files main.cl and main.pro with given code.

Here we define two new predicates — fibonacci(N,F) to calculate Nth Fibonacci number and loop(N) to output it. We don’t use memoization to store already calculated numbers, so this implementation is rather inefficient. Note the way the predicates are defined — each predicate is written as one clause using conjunction , and disjunction ; of elementary predicates (instead of breaking them in several clauses which use only disjunction). 

% main.cl
class main
    open core

predicates
    classInfo : core::classInfo.
    fibonacci : (integer N, integer F) procedure (i,o).
    loop : (integer N) procedure (i).
predicates
    run : core::runnable.

end class main

% main.pro
implement main
    open core

constants
    className = "main".
    classVersion = "".

clauses
    classInfo(className, classVersion).
    fibonacci(N,F) :- 
        N < 3, !, F = 1;
        fibonacci(N-1,F1), fibonacci(N-2,F2), F = F1 + F2.
    loop(N) :-
        ( N = 1, !, fibonacci(1,F);
          loop(N-1), fibonacci(N,F) ),
        stdio::write(F, ", ").
        
clauses
    run():-
        console::init(),
        loop(16),
        stdio::write("..."),
        programControl::sleep(1000),
        succeed().
end implement main

goal
    mainExe::run(main::run).