focusByClass :: String -> X()
focusByClass n = do
  ws <- gets $ W.index . windowset
  app <- findByQuery ws (className =? n)
  whenJust app focus

findByQuery :: [Window] -> Query Bool -> X (Maybe Window)
findByQuery ws q = do
  w <- filterM (runQuery q) ws
  case (length w > 0) of
    True -> return $ Just $ head w
    False -> return Nothing