cmdargsはargsと同時にhelpを設定するとシぬ

clOptions :: CommandLineOptions
clOptions = CommandLineOptions
  { frontend    = "vty"   &= help "The frontend to use"
  , startOnLine = Nothing &= help "Open the (last) file on line NUM"
  , files       = []      &= help "FILES..." &= args  -- ここ
  }

clOptions :: CommandLineOptions
clOptions = CommandLineOptions
  { frontend    = "vty"   &= help "The frontend to use"
  , startOnLine = Nothing &= help "Open the (last) file on line NUM"
  , files       = []      &= args  -- ここ
  }