haskell itoa implementation

itoa.hs

itoa :: (Integral a) => a -> String
itoa x
  | x == 0 = "0"
  | x == 1 = "1"
  | x == 2 = "2"
  | x == 3 = "3"
  | x == 4 = "4"
  | x == 5 = "5"
  | x == 6 = "6"
  | x == 7 = "7"
  | x == 8 = "8"
  | x == 9 = "9"
  | x < 0 = "-" ++ itoa (abs x)
  | x > 0 = itoa (quot x 10) ++ itoa (x `mod` 10)