[xmonad] ManageHook and doF

Hi! I have manageHook like this: myManageHook = composeAll [ className =? "Firefox" --> doF(W.shift "web"), className =? "Gajim.py" --> doF(W.shift "chat"), className =? "Deadbeef" --> doF(W.shift "music"), title =? "Gajim" --> doFloat, className =? "MPlayer" --> doCenterFloat, ] so, if some workspace does not exist by some reason, the new window will appear on current workspace. How to chek if workspace exists and create it before "W.shift" action? I think addWorkspace from XMonad.Actions.DynamicWorkspaces can do this, but I don't know haskell well to write some function that can be used with doF.