move Layout stuff into class (hokey first cut).

Config.hs

@@ -92,10 +92,10 @@ borderWidth = 1
 -- |
 -- The default set of tiling algorithms
 --
-defaultLayouts :: [Layout Window]
-defaultLayouts = [ tiled
-                 , mirror tiled
-                 , full
+defaultLayouts :: [SomeLayout Window]
+defaultLayouts = [ SomeLayout tiled
+                 , SomeLayout $ mirror tiled
+                 , SomeLayout full
 
                  -- Extension-provided layouts
                  ]

Main.hs

@@ -55,7 +55,7 @@ main = do
                | otherwise = new workspaces $ zipWith SD xinesc gaps
         gaps = take (length xinesc) $ defaultGaps ++ repeat (0,0,0,0)
 
-        safeLayouts = case defaultLayouts of [] -> (full, []); (x:xs) -> (x,xs)
+        safeLayouts = case defaultLayouts of [] -> (SomeLayout full, []); (x:xs) -> (x,xs)
         cf = XConf
             { display       = dpy
             , theRoot       = rootw

Operations.hs

@@ -138,7 +138,7 @@ windows f = do
 
         -- just the tiled windows:
         -- now tile the windows on this workspace, modified by the gap
-        (rs, ml') <- runLayout l viewrect tiled `catchX` runLayout full viewrect tiled
+        (rs, ml') <- runLayout l viewrect tiled `catchX` runLayout (SomeLayout full) viewrect tiled
         mapM_ (uncurry tileWindow) rs
         whenJust ml' $ \l' -> modify $ \ss ->
                               ss { layouts = M.adjust (first (const l')) n (layouts ss) }
@@ -351,18 +351,18 @@ instance Message IncMasterN
 
 -- simple fullscreen mode, just render all windows fullscreen.
 -- a plea for tuple sections: map . (,sc)
-full :: Layout a
-full = Layout { doLayout     = \sc (W.Stack f _ _) -> return ([(f, sc)],Nothing)
-              , modifyLayout = const (return Nothing) } -- no changes
+full :: OldLayout a
+full = OldLayout { doLayout'     = \sc (W.Stack f _ _) -> return ([(f, sc)],Nothing)
+                 , modifyLayout' = const (return Nothing) } -- no changes
 
 --
 -- The tiling mode of xmonad, and its operations.
 --
-tall :: Int -> Rational -> Rational -> Layout a
+tall :: Int -> Rational -> Rational -> OldLayout a
 tall nmaster delta frac =
-    Layout { doLayout     = \r -> return . (\x->(x,Nothing)) .
+    OldLayout { doLayout' = \r -> return . (\x->(x,Nothing)) .
                                   ap zip (tile frac r nmaster . length) . W.integrate
-           , modifyLayout = \m -> return $ msum [fmap resize     (fromMessage m)
+              , modifyLayout' = \m -> return $ msum [fmap resize     (fromMessage m)
                                                     ,fmap incmastern (fromMessage m)] }
 
     where resize Shrink = tall nmaster delta (max 0 $ frac-delta)
@@ -374,11 +374,11 @@ mirrorRect :: Rectangle -> Rectangle
 mirrorRect (Rectangle rx ry rw rh) = (Rectangle ry rx rh rw)
 
 -- | Mirror a layout, compute its 90 degree rotated form.
-mirror :: Layout a -> Layout a
-mirror (Layout { doLayout = dl, modifyLayout = ml }) =
-    Layout { doLayout     = \sc w -> do (wrs, ml') <- dl (mirrorRect sc) w
+mirror :: Layout l a => l a -> OldLayout a
+mirror l =
+    OldLayout { doLayout' = \sc w -> do (wrs, ml') <- doLayout l (mirrorRect sc) w
                                         return (map (second mirrorRect) wrs, mirror `fmap` ml')
-           , modifyLayout = fmap (fmap mirror) . ml }
+              , modifyLayout' = fmap (fmap mirror) . modifyLayout l }
 
 -- | tile.  Compute the positions for windows using the default 2 pane tiling algorithm.
 --

XMonad.hs

@@ -15,7 +15,7 @@
 -----------------------------------------------------------------------------
 
 module XMonad (
-    X, WindowSet, WorkspaceId, ScreenId(..), ScreenDetail(..), XState(..), XConf(..), Layout(..),
+    X, WindowSet, WorkspaceId, ScreenId(..), ScreenDetail(..), XState(..), XConf(..), Layout(..), OldLayout(..), SomeLayout(..),
     Typeable, Message, SomeMessage(..), fromMessage, runLayout,
     runX, catchX, io, catchIO, withDisplay, withWindowSet, isRoot, getAtom, spawn, restart, trace, whenJust, whenX,
     atom_WM_STATE, atom_WM_PROTOCOLS, atom_WM_DELETE_WINDOW
@@ -43,7 +43,7 @@ data XState = XState
     { windowset    :: !WindowSet           -- ^ workspace list
     , mapped       :: !(S.Set Window)      -- ^ the Set of mapped windows
     , waitingUnmap :: !(M.Map Window Int)  -- ^ the number of expected UnmapEvents
-    , layouts      :: !(M.Map WorkspaceId (Layout Window, [Layout Window]))
+    , layouts      :: !(M.Map WorkspaceId (SomeLayout Window, [SomeLayout Window]))
                        -- ^ mapping of workspaces to descriptions of their layouts
     , dragging     :: !(Maybe (Position -> Position -> X (), X ())) }
 data XConf = XConf
@@ -131,10 +131,27 @@ atom_WM_STATE           = getAtom "WM_STATE"
 -- that message and the screen is not refreshed.  Otherwise, 'modifyLayout'
 -- returns an updated 'Layout' and the screen is refreshed.
 --
-data Layout a = Layout { doLayout     :: Rectangle -> Stack a -> X ([(a, Rectangle)], Maybe (Layout a))
-                       , modifyLayout :: SomeMessage -> X (Maybe (Layout a)) }
+data OldLayout a =
+    OldLayout { doLayout'     :: Rectangle -> Stack a -> X ([(a, Rectangle)], Maybe (OldLayout a))
+              , modifyLayout' :: SomeMessage -> X (Maybe (OldLayout a)) }
 
-runLayout :: Layout a -> Rectangle -> StackOrNot a -> X ([(a, Rectangle)], Maybe (Layout a))
+data SomeLayout a = forall l. Layout l a => SomeLayout (l a)
+
+class 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 OldLayout a where
+    doLayout = doLayout'
+    modifyLayout = modifyLayout'
+
+instance Layout SomeLayout a where
+    doLayout (SomeLayout l) r s = do (ars, ml') <- doLayout l r s
+                                     return (ars, SomeLayout `fmap` ml' )
+    modifyLayout (SomeLayout l) m = do ml' <- modifyLayout l m
+                                       return (SomeLayout `fmap` ml')
+
+runLayout :: Layout l a => l a -> Rectangle -> StackOrNot a -> X ([(a, Rectangle)], Maybe (l a))
 runLayout l r = maybe (return ([], Nothing)) (doLayout l r)
 
 -- | Based on ideas in /An Extensible Dynamically-Typed Hierarchy of Exceptions/,