3, John Smith wrote:

I would like to formally propose that Monad become a subclass of Applicative

I'm not in favour of this change because of the code breakage issue. However, I think that an acceptable plan (mentioned elsewhere on the list, but doesn't seem to have had any subsequent discussion) would be to introduce a GHC warning for such cases: "Warning: you are declaring a Monad instance for MyMonad without a corresponding Applicative instance. This will be an error in GHC 7.2" Then in 7.2 you can remove the warning and change the class hierarchy. (Substitute 7.4 for 7.2 if you think we need more time for library authors to update, or if you add the warning only to the 7.2 series). Cheers, Max