On Sunday 02 January 2011 13:04:30 you wrote:
The patches attached to http://hackage.haskell.org/trac/ghc/ticket/4834 make Applicative a superclass of Monad. Default definitions are provided for backwards compatibility.
I looked at the Prelude of the referenced documentation in the ticket: http://bifunctor.homelinux.net/~bas/doc/ghc/html/libraries/base-4.4.0.0/Prel... Would it be useful to include liftM and ap in the Prelude, so that you can use it as a default implementation for fmap, when defining Functor instances? Then you can write... instance Functor Something where fmap = liftM instance Applicative Something where pure x = ... (<*>) = ap instance Monad Something where (>>=) = ... This way you don't need to write explicit implementations of fmap and <*> for every monad you define. An alternative name for liftM would be fmapMonad... There is a similar approach in Data.Traversable: fmapDefault :: Traversable t => (a -> b) -> t a -> t b However as Functor, Applicative and Monad are part of the Prelude, it might be useful, to include a default implementation for fmap in the Prelude. Regards Jan