make layouts preserved over restart

Config.hs-boot

@@ -1,8 +1,9 @@
 module Config where
 import Graphics.X11.Xlib.Types (Dimension)
-import Graphics.X11.Xlib (KeyMask)
+import Graphics.X11.Xlib (KeyMask,Window)
 import XMonad
 borderWidth :: Dimension
 logHook     :: X ()
 numlockMask :: KeyMask
 workspaces :: [WorkspaceId]
+defaultLayouts :: [SomeLayout Window]

Operations.hs

@@ -18,7 +18,7 @@ module Operations where
 
 import XMonad
 import qualified StackSet as W
-import {-# SOURCE #-} Config (borderWidth,logHook,numlockMask)
+import {-# SOURCE #-} Config (borderWidth,logHook,numlockMask,defaultLayouts)
 
 import Data.Maybe
 import Data.List            (nub, (\\), find)
@@ -105,6 +105,12 @@ kill = withDisplay $ \d -> withFocused $ \w -> do
 data UnDoLayout = UnDoLayout deriving ( Typeable, Eq )
 instance Message UnDoLayout
 
+instance Read (SomeLayout Window) where
+    readsPrec _ = readLayout defaultLayouts
+instance Layout SomeLayout Window where
+    doLayout (SomeLayout l) r s = fmap (fmap $ fmap SomeLayout) $ doLayout l r s
+    modifyLayout (SomeLayout l) = fmap (fmap SomeLayout) . modifyLayout l
+
 -- | windows. Modify the current window list with a pure function, and refresh
 windows :: (WindowSet -> WindowSet) -> X ()
 windows f = do

XMonad.hs

@@ -131,10 +131,9 @@ atom_WM_STATE           = getAtom "WM_STATE"
 -- returns an updated 'Layout' and the screen is refreshed.
 --
 data SomeLayout a = forall l. Layout l a => SomeLayout (l a)
+
 instance Show (SomeLayout a) where
     show (SomeLayout l) = show l
-instance Read (SomeLayout a) where
-    readsPrec _ _ = [] -- We can't read an existential type!!!
 
 readLayout :: [SomeLayout a] -> String -> [(SomeLayout a, String)]
 readLayout ls s = concatMap rl ls
@@ -146,10 +145,6 @@ class (Show (layout a), Read (layout a)) => Layout layout a where
     doLayout :: layout a -> Rectangle -> Stack a -> X ([(a, Rectangle)], Maybe (layout a))
     modifyLayout :: layout a -> SomeMessage -> X (Maybe (layout a))
 
-instance Layout SomeLayout a where
-    doLayout (SomeLayout l) r s = fmap (fmap $ fmap SomeLayout) $ doLayout l r s
-    modifyLayout (SomeLayout l) = fmap (fmap SomeLayout) . modifyLayout l
-
 runLayout :: Layout l a => l a -> Rectangle -> StackOrNot a -> X ([(a, Rectangle)], Maybe (l a))
 runLayout l r = maybe (return ([], Nothing)) (doLayout l r)