    ----------------------------------------------------------------------------
    -- |
    -- Module      :  XMonad.Hooks.WorkspaceByPos
    -- Copyright   :  (c) Jan Vornberger 2009
    -- License     :  BSD3-style (see LICENSE)
    --
    -- Maintainer  :  jan.vornberger@informatik.uni-oldenburg.de
    -- Stability   :  unstable
    -- Portability :  not portable
    --
    -- Useful in a dual-head setup: Looks at the requested geometry of
    -- new windows and moves them to the workspace of the non-focused
    -- screen if necessary.
    --
    -----------------------------------------------------------------------------

    module XMonad.Hooks.WorkspaceByPos (
        -- * Usage
        -- $usage
        workspaceByPos
        ) where

    import XMonad
    import qualified XMonad.StackSet as W
    import XMonad.Util.XUtils (fi)

    import Data.Maybe
    import Control.Applicative((<$>))
    import Control.Monad.Error ((<=<),guard,lift,runErrorT,throwError)

    -- $usage
    -- You can use this module with the following in your @~\/.xmonad\/xmonad.hs@:
    --
    -- > import XMonad.Hooks.WorkspaceByPos
    -- >
    -- > myManageHook = workspaceByPos <+> manageHook def
    -- >
    -- > main = xmonad def { manageHook = myManageHook }

    workspaceByPos :: ManageHook
    workspaceByPos = (maybe idHook doShift <=< liftX . needsMoving) =<< ask

    needsMoving :: Window -> X (Maybe WorkspaceId)
    needsMoving w = withDisplay $ \d -> do
        -- only relocate windows with non-zero position
        wa <- io $ getWindowAttributes d w
        fmap (const Nothing `either` Just) . runErrorT $ do
            guard $ wa_x wa /= 0 || wa_y wa /= 0
            ws <- gets windowset
            sc <- lift $ fromMaybe (W.current ws)
                    <$> pointScreen (fi $ wa_x wa) (fi $ wa_y wa)
            Just wkspc <- lift $ screenWorkspace (W.screen sc)
            guard $ W.currentTag ws /= wkspc
            return wkspc `asTypeOf` throwError ""