Lib.hs

import GHC.Show (intToDigit)

-- | Fast hex representation of Word8
showHex :: Word8 -> ShowS
showHex n0 = showIt (1 :: Int) (quotRem n0 16)
   where
    showIt x (n,d) r = seq c $ -- stricter than necessary
      case x of
        0 -> r'
        _ -> showIt (x-1) (quotRem n 16) r'
     where
      c  = intToDigit (fromIntegral d)
      r' = c : r