Dear GHC developers, ghc-6.4 documentation specifies about Map.insertWith " insertWith :: Ord k => (a -> a -> a) -> k -> a -> Map k a -> Map k a O(log n). Insert with a combining function. " This description is not sufficient. For example, in insertWith (\ a1 a2 -> a1) k a3 mp the doc does not tell what value overrides on the key overlap, a3 or the one in mp. The usage of the GHC library for Set and Map will become much easier if you fix this documentation point on all updating functions for Set and Map which use a combining function. Regards, ----------------- Serge Mechveliani mechvel@botik.ru