Hi all, I was toying with Haskell classes and came across Functor-Applicative-Monad proposal[1]. It shows out that adding a super class (Applicative) to a class (Monad) is not an easy task when the class hierarchy is already in use. In this case it result in stepwise approach (step1 e. g. [2]) in order not to break already existing code which uses Monad. I am interested in other examples of such changes. Which alterings of your class hierarchy do you usually need when rewriting your code? I don't mean only adding superclass here, other modifications could be also handy, e. g. dropping out a class or splitting a class into two. Can you point me to some actual examples on real source code? How do you deal with this kind of problem on your projects? Thanks for a reply :) FF [1] http://www.haskell.org/haskellwiki/Functor-Applicative-Monad_Proposal [2] https://ghc.haskell.org/trac/ghc/ticket/8004