The idea of unifying the interface of apis is pretty good IMHO, but I have to say something about this bit "(about objects and abstract data types) No existing user code can do anything useful with your instances." I don't think that's actually true in the case of haskell Abstract Data Types. I mean, sure, the existing code base can't do anything magic with the types, but at least declaring "deriving Typeable, Data" allows you to make some magic.