add Show instance to Layout

Operations.hs

@@ -351,14 +351,14 @@ instance Message IncMasterN
 
 -- simple fullscreen mode, just render all windows fullscreen.
 -- a plea for tuple sections: map . (,sc)
-data Full a = Full
+data Full a = Full deriving Show
 instance Layout Full a where
     doLayout Full sc (W.Stack f _ _) = return ([(f, sc)], Nothing)
     modifyLayout Full _ = return Nothing -- no changes
 --
 -- The tiling mode of xmonad, and its operations.
 --
-data Tall a = Tall Int Rational Rational
+data Tall a = Tall Int Rational Rational deriving Show
 instance Layout Tall a where
     doLayout (Tall nmaster _ frac) r =
         return . (\x->(x,Nothing)) .
@@ -376,6 +376,8 @@ mirrorRect (Rectangle rx ry rw rh) = (Rectangle ry rx rh rw)
 
 -- | Mirror a layout, compute its 90 degree rotated form.
 data Mirror a = forall l. Layout l a => Mirror (l a)
+instance Show (Mirror a) where
+    show (Mirror l) = "Mirror "++show l
 instance Layout Mirror a where
     doLayout (Mirror l) r s = do (wrs, ml') <- doLayout l (mirrorRect r) s
                                  return (map (second mirrorRect) wrs, Mirror `fmap` ml')

XMonad.hs

@@ -132,8 +132,10 @@ 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
 
-class Layout layout a where
+class Show (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))