Haskell program to calculate factorial of a number

factorial.hs

-- $ ./factorial 10
-- 3628800
import System.Environment

main = do
    args <- getArgs
    let n = args !! 0 
    putStrLn (show (factorial (read n)))

factorial :: (Integral a) => a -> a
factorial 0 = 1
factorial n = n * factorial (n - 1)