Hey, I was wondering how difficult it would be to improve handling of casts, as follows: when looking at Core, I see things like (\ (ds_dcKZ :: Data.TrieMap.TrieKey.TrieMap (Data.TrieMap.Regular.Base.App f_XcwB k_XcwD) a_acAi) -> f_scPr (ds_dcKZ `cast` (trans (Data.TrieMap.Regular.App.TFCo:R:TrieMapAppa f_XcwB k_XcwD a_acAi) (Data.TrieMap.Regular.App.NTCo:R:TrieMapAppa f_XcwB k_XcwD a_acAi) :: Data.TrieMap.TrieKey.TrieMap (Data.TrieMap.Regular.Base.App f_XcwB k_XcwD) a_acAi ~ Data.TrieMap.Regular.Class.TrieMapT f_XcwB k_XcwD a_acAi))) which is equivalent to a single cast of f. I get that generalized newtype deriving does something like this automatically -- unfortunately, at the moment, I'm using a class with associated types, so I can't do that. How difficult would it be to identify and rewrite these, when they appear in non-recursive lets? (I'm actually experimenting with implementing the change myself, but I've never hacked GHC before, so we'll see how it goes...) Louis Wasserman wasserman.louis@gmail.com http://profiles.google.com/wasserman.louis