lexeme :: BS.ByteString -> BS.ByteString -> Maybe BS.ByteString
lexeme l t
  | l `BS.isPrefixOf` t = Just $ dropSpaces $ BS.drop (BS.length l) t
  | otherwise = Nothing
lexeme :: BS.ByteString -> BS.ByteString -> Maybe BS.ByteString
lexeme l t
  | l `BS.isPrefixOf` t = Just $ dropSpaces $ BS.drop (BS.length l) t
  | otherwise = Nothing
lexeme l t
  | l `BS.isPrefixOf` t = Just $ dropSpaces $ BS.drop (BS.length l) t
  | otherwise = Nothing