Hi, this is a step forward in the direction of the type classes cleanup I've been proposing recently. The basic idea is to completely hide the Layout implementation to LayoutModifiers and LayoutCombinators. This way we can extend the LayoutClass without messing up the whole repository. This should also let us remove a lot of duplicate code and let the developers not to rewrite always the same stuff with high probability of bugs. This way we could also reject any code that has a (wrs,ml) <- doLayout in a LayoutClass instance...;) While there seems to be not much use for such a class (well, PerWorksapce, ToggleLayouts, MultiToggle, LayoutCombinators, the layout selector, and so on...;), while implementing it I had the feeling it could be quite a powerful tool. Imagine to run 2 layouts and then combine their results with pure code with "combineResult"... I don't know, but that could be fun. Still I have some troubles in implementing the handleMessage methond for CombinedLayout - and in deciding the type of comboHandleMessage. If we switch layout, the first one should receive an Hide. Should I take care of that in the class? In the instance? David, any idea? That following would be the implementation of a simple Toggle layout combinator. It works (sendMessage Toogle will make it switch), but I still have to find a clean solution to hide the first layout, otherwise decorations will be floating around d forever...;) Any idea? TIA Andrea data ToggleLayout a = TL Bool deriving (Read,Show) instance LayoutCombinator ToggleLay a where chooser (TL b) = if b then DoFirst else DoSecond comboHandleMess (TL b) _ _ m | Just Togg <- fromMessage m = return $ TL (not b) | otherwise = return (TL b) data ToggleLayoutMsg = Toggle deriving (Read,Show,Typeable) instance Message ToggleLayoutMsg toggle :: l1 a -> l2 a -> CombinedLayout ToggleLayout l1 l2 a toggle = CombinedLayout (TL True) to use as: toggle Full tabbed Tue Jan 29 18:25:24 CET 2008 Andrea Rossato * The start of a LayoutCombinator class with a CombinedLayout