Fibonacci on Haskell

fib.hs

import System.Environment (getArgs)

main :: IO ()
main = do
  args <- getArgs
  let n = read $ head args :: Int
  putStrLn . show $ fib n

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

fib_memoize.hs

import System.Environment (getArgs)

main :: IO ()
main = do
  args <- getArgs
  let n = read $ head args :: Int
  putStrLn . show $ fib n

fib :: Int -> Integer
fib = (map fib' [0 ..] !!)
   where fib' 0 = 0
         fib' 1 = 1
         fib' n = fib (n - 1) + fib (n - 2)