Factorial in Picat

Example for versions Picat 0.7

This example implements recursive factorial definition using a function. 

factorial(0) = 1.
factorial(N) = F, N > 0 => F = N * factorial(N - 1).

main =>
     foreach (I in 0 .. 16)
          writef("%w! = %w\n", I, factorial(I))
     end.