binary exponentiation. haskell.

binexp.hs

import System.Environment (getArgs)

myPow x y
    | y < 0 = error "neg."
    | y == 0 = 1
    | otherwise = pow' y x
    where
        pow' kth cur
            | kth == 1 = cur
            | odd kth = cur * pow' (kth `quot` 2) (cur * cur)
            | otherwise = pow' (kth `quot` 2) (cur * cur)

main = do
    ints <- fmap (map read) $ getArgs :: IO [Int]
    print $ (head ints) `myPow` (last ints)