portOpt l = fmap (maybe mempty $ fromLens l . Port) . optional . OB.option
  (maybeReader $ fmap fromInteger . readMaybe)
portOpt l = fmap (maybe mempty $ fromLens l . Port) . optional . OB.option
  (maybeReader $ fmap fromInteger . readMaybe)
portOpt l = fmap (maybe mempty $ fromLens l . Port) . optional . OB.option
  (maybeReader $ fmap fromInteger . readMaybe)