Hi all, (This email is partly a resend of content attached along with a patch, which I realize folks might not have seen, since I sent a fixed version of that patch. If you come across this twice, and find it as boring the second time as the first, my apologies.) There's design problem with some of the recently-introduced self-modifying layout modifiers, which include Decorations and SimpleStacking. The trouble is that while it's easy for a Layout to modify itself in response to an event, there's no safe way for a layout to modify itself in during a doLayout call. One answer to that is to simply state that "layouts should not do that." This seems an unsatisfying answer to me, as we've already got two valid uses--one already refactored into LayoutHooks, an inherently buggy module. The trouble is that within doLayout, there's no way for a layout to modify itself, because it can't tell which layout it is... and because it may not be a "root" layout at all, but some intermediate modified layout. There seems to be a simple solution: data Layout a = Layout { doLayout :: Rectangle -> Stack a -> X ([(a, Rectangle)], Maybe (Layout a)) , modifyLayout :: SomeMessage -> X (Maybe (Layout a)) } so doLayout can modify itself. This makes all the Layout transformers a little harder to write, but a helper module ought to be able to fix that. And it makes me wonder yet again whether we should be defining a class class Layout l a where doLayout :: l -> X Rectangle -> Stack a -> X ([(a, Rectangle)], Maybe (Layout a) modifyLayout :: l -> SomeMessage -> X (Maybe (Layout a)) serializeLayout :: l -> String readLayout :: String -> Maybe (l, String) -- or some other parser-like thing data Layout a = forall l. Layout l a => Layout a This might lend itself to somewhat prettier Layout code that is more "data-structure-based" rather than self-modifying-function-based. I imagine this would lead to friendly interfaces for easy-to-write layout modifiers. David P.S. I'd be curious to see implemented a "popularity-contest" module for xmonad once we've got serialization, which could use the logging mechanism to report on the most frequently used layouts. And yes, this would be in XMonadContrib and only manually enabled. I have no idea how many people are actually using Tabbed, and how likely this is to break folks' Config files.