Comb.hs

makeBitString :: Int -> [String]
makeBitString 0 = []
makeBitString 1 = ["0","1"]
makeBitString w = map ('0':) (makeBitString (w-1)) ++ map ('1':) (makeBitString (w-1))

makeMaskZeroString :: Int -> [String]
makeMaskZeroString w = ((map oneToMask) . makeBitString) w
  where
    oneToMask :: String -> String
    oneToMask = (map (\c -> if c == '1' then '*' else c))