X.L.LayoutScreens split current screen

This patch will allow the user to split the currently focused screen instead of all screens together. This is usefull for multiscreen users who have functioning xinerama, but wish to split one of the screens.

XMonad/Layout/LayoutScreens.hs

@@ -16,7 +16,7 @@
 module XMonad.Layout.LayoutScreens (
                                     -- * Usage
                                     -- $usage
-                                    layoutScreens, fixedLayout
+                                    layoutScreens, layoutSplitScreen, fixedLayout
                                    ) where
 
 import XMonad
@@ -55,6 +55,7 @@ import qualified XMonad.StackSet as W
 -- For detailed instructions on editing your key bindings, see
 -- "XMonad.Doc.Extending#Editing_key_bindings".
 
+-- | Modify all screens.
 layoutScreens :: LayoutClass l Int => Int -> l Int -> X ()
 layoutScreens nscr _ | nscr < 1 = trace $ "Can't layoutScreens with only " ++ show nscr ++ " screens."
 layoutScreens nscr l =
@@ -67,6 +68,20 @@ layoutScreens nscr l =
                   , W.visible = zipWith3 W.Screen xs [1 ..] $ map SD ss
                   , W.hidden  = ys }
 
+-- | Modify current screen.
+layoutSplitScreen :: LayoutClass l Int => Int -> l Int -> X ()
+layoutSplitScreen nscr _ | nscr < 1 = trace $ "Can't layoutSplitScreen with only " ++ show nscr ++ " screens."
+layoutSplitScreen nscr l =
+    do rect <- gets $ screenRect . W.screenDetail . W.current . windowset
+       (wss, _) <- runLayout (W.Workspace "" l (Just $ W.Stack { W.focus=1, W.up=[],W.down=[1..nscr-1] })) rect
+       windows $ \ws@(W.StackSet { W.current = c, W.visible = vs, W.hidden = hs }) ->
+           let (x:xs, ys) = splitAt nscr $ W.workspace c : hs
+               s:ss = map snd wss
+           in  ws { W.current = W.Screen x (W.screen c) (SD s)
+                  , W.visible = (zipWith3 W.Screen xs [(W.screen c+1) ..] $ map SD ss) ++
+                                map (\v -> if W.screen v>W.screen c then v{W.screen = W.screen v + fromIntegral (nscr-1)} else v) vs
+                  , W.hidden  = ys }
+
 getWindowRectangle :: Window -> X Rectangle
 getWindowRectangle w = withDisplay $ \d ->
     do a <- io $ getWindowAttributes d w