import Control.Exception (IOException, try)

    Nothing -> do
      hPutStrLn stderr $ "Could not resolve nameserver " ++ nsHost

    Left err -> do
      hPutStrLn stderr $ show err

    Just ipStr -> do

    Right (Just ipStr) -> do

    Right Nothing -> do
      hPutStrLn stderr $ "No server found for " ++ domain
      pure []

resolveNameServer :: String -> IO (Maybe String)

resolveNameServer :: String -> IO (Either IOException (Maybe String))

  | all (`elem` (".0123456789" :: String)) host = pure (Just host)  -- already numeric

  | all (`elem` (".0123456789" :: String)) host =
      pure (Right (Just host))

      infos <- getAddrInfo (Just defaultHints) (Just host) (Just "53")
      pure $ fmap (stripPort . show . addrAddress) (listToMaybe infos)

      result <- try $
        getAddrInfo (Just defaultHints) (Just host) (Just "53")
      case result of
        Left err ->
          pure (Left (err))
        Right infos ->
          case listToMaybe infos of
            Nothing ->
              pure (Right (Nothing))
            Just info ->
              let ip = stripPort . show . addrAddress $ info
              in pure (Right (Just ip))

  safeMain `catch` \(e :: SomeException) -> hPutStrLn stderr $ "[ERROR] " ++ show e
safeMain :: IO ()
safeMain = do

      exitFailure

          putStrLn $ "the IP is " ++ show ip