module NFib where

instruction primadd "addint" :: Int! -> Int! -> Int!
instruction primsub "subint" :: Int! -> Int! -> Int!

main  = nfib 27

-- strict nfib
nfib n  = case n of
            0  -> 1
            1  -> 1
            n  -> let! x = let! x2 = (let! n2 = primsub n 2 in nfib n2)
                                x1 = (let! n1 = primsub n 1 in nfib n1)
                           in primadd x1 x2
                  in primadd 1 x