On Mon, 4 Feb 2008, Miguel Mitrofanov wrote: > > Problem is that from the idea Functor is a superclass of Monad, with > > the > > property that "fmap == liftM". > > [cut] > > > The second relation can even not be expressed in Haskell 98. > > Erm... > > class Functor f where > fmap :: (a -> b) -> f a -> f b > class Functor m => Monad m where > return :: a -> m a > join :: m (m a) -> m a > > bind :: Monad m => m a -> (a -> m b) -> m b > bind mx f = join $ fmap f mx
nice > Now liftM must be exactly equal to fmap. How do you convince the compiler that 'join (fmap return x) == x' ? _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
