moveW :: Position -> Position -> Window -> X ()
moveW x y w = withDisplay $ moveWindow' w

moveWindow' :: Position -> Position -> Window -> Display -> X ()
moveWindow' x y w d = do float w
                         io $ moveWindow d w x y

fromWindowOp :: (Window -> X()) -> ManageHook
fromWindowOp fn = ask >>= \w -> liftX (fn w) >> doF id

doMove :: Position -> Position -> ManageHook
doMove x y = fromWindowOp (moveW x y)
                          
...

[ className =? "xxx" --> doMove 150 300,