module Fibonacci;
  open import Stdlib.Prelude;

  fib : Nat  Nat  Nat  Nat;
  fib zero x1 _ := x1;
  fib (suc n) x1 x2 := fib n x2 (x1 + x2);

  fibonacci : Nat  Nat;
  fibonacci n := fib n 0 1;

  main : IO;
  main := putStrLn (natToStr (fibonacci 25));
end;