LeftPad in Haskell

leftPadInternal :: String -> Int -> Char -> String
leftPadInternal str rem ch = 
  if (rem <= 0) then 
    str
  else
	leftPadInternal ([ch] ++ str) (rem - 1) ch 
	    
leftPad :: String -> Int -> Maybe Char -> String
leftPad str len ch = 
  case ch of 
	Just c -> leftPadInternal str (len - length str) c
	Nothing -> leftPadInternal str (len - length str) '.'
main :: IO ()
main = do let z = leftPad "1" 1 Nothing
          putStrLn $ "" ++ show z
          let z = leftPad "2" 2 Nothing
          putStrLn $ "" ++ show z
          let z = leftPad "3" 3 Nothing
          putStrLn $ "" ++ show z
          let z = leftPad "4" 4 Nothing
          putStrLn $ "" ++ show z
          let z = leftPad "5" 5 Nothing
          putStrLn $ "" ++ show z
          let z = leftPad "hello" 7 Nothing
          putStrLn $ "" ++ show z
          let z = leftPad "foo" 6 Nothing
          putStrLn $ "" ++ show z
          let z = leftPad "foo" 3 Nothing
          putStrLn $ "" ++ show z
          let z = leftPad "foobar" 3 Nothing
          putStrLn $ "" ++ show z
          let z = leftPad "foo" 6 (Just '?')
          putStrLn $ "" ++ show z