Status: New Owner: vogt.a...@gmail.com Labels: Type-Enhancement Priority-Low Component-Core Component-Contrib New issue 522 by vogt.a...@gmail.com: get default value from XState for XMonad.Util.Invisible http://code.google.com/p/xmonad/issues/detail?id=522 Currently xmonad layouts have to be instances of Show so that the state can be saved between restarts. XMonad.Util.Invisible works for state that can be replaced without looking at the user's configuration. To work around this, modules like XMonad.Util.WindowProperties have to be written for layouts like XMonad.Layout.IM, when it would have been easier on everybody to pass a function (ie ManageHook) to the IM layout. The attached patch to xmonad core adds Data instances for layouts. The module MergeLayout provides a startupHook that replaces the (I Nothing) that xmonad gets on restart with what's in the xmonad.hs at the same spot. Pushing this would break all layouts. Fixing them involves adding Data (and Typeable) instances or contexts to existing instances. Normally that involves just a `deriving(Data,Typeable)'. I can't convince ghc to generate the instances in some cases: I manually wrote instances for Mirror and Choose in the dpatch file attached. Finally there is a possible objection that the Data instance will break abstractions: having a (derived) Data instance allows access to the constructors. Most of the time I think constructors are not exported to make some changes easier, rather than to make sure invalid values cannot be constructed (ex. Data.Map). Attachments: require-layouts-to-be-instances-of-data.dpatch 8.7 KB MergeLayout.hs 1.5 KB