gf-core/transfer/examples/fib.tr

import nat ;

fib : Int -> Int ;
fib 0 = 1 ;
fib 1 = 1 ;
fib n = fib (n-1) + fib (n-2) ;

fibNat : Nat -> Nat ;
fibNat Zero = Succ Zero ;
fibNat (Succ Zero) = Succ Zero ;
fibNat (Succ (Succ n)) = plus (fibNat (Succ n)) (fibNat n) ;