optparse-applicative for cli params of Maybne NonEmptyList

cli.hs

#!/usr/bin/env stack
{-      stack
        script
        --resolver lts-18.28
        --package async
        --package optparse-applicative
        --package text
-}
import           Data.List.NonEmpty  (NonEmpty, fromList)
import           Data.Semigroup      ((<>))
import           Options.Applicative (Alternative (some), Mod, OptionFields,
                                      Parser, auto, execParser, fullDesc,
                                      header, help, helper, info, long, metavar,
                                      option, optional, progDesc, short, str,
                                      (<**>))

data Cli = Cli
  {
    port      :: Int
  , hostnames :: Maybe (NonEmpty String)
  } deriving (Show)

main :: IO ()
main = execParser clis >>= print
  where
    clis = info (cli <**> helper )
                (fullDesc
                <> progDesc "Print a greeting for TARGET"
                <> header "hello - a test for optparse-applicative")

cli :: Parser Cli
cli = Cli
  <$> option auto ( long "port"
                  <> short 'p'
                  <> metavar "PORT"
                  <> help "port number" )
  <*> multiString ( long  "hostname"
                  <> short 'h'
                  <> metavar "HOSTNAME"
                  <> help "hostname")

multiString' :: Mod OptionFields [String] -> Parser (NonEmpty String )
multiString' desc = fromList . concat <$> some single
  where
    single = option (str >>= parseStringList) desc

multiString :: Mod OptionFields [String] -> Parser (Maybe (NonEmpty String))
multiString = optional . multiString'

parseStringList :: Monad m => String -> m [String]
parseStringList = return . words