Then it would be: class Functor f where fmap :: (a -> b) -> f a -> f b class (Functor f) => Pointed f where pure :: a -> f a class (Pointed f) => Applicative f where (<*>) :: f (a -> b) -> f a -> f b class (Applicative f) => Monad f where join :: f (f a) -> f a This would be a great idea, for the sake of logic, first (a monad which is not a functor doesn't make sense), and also to eliminate redudancy (fmap = liftM, ap = (<*>), etc.) 2010/5/20 Tony Morris <tonymorris@gmail.com>
Ivan Miljenovic wrote:
On 20 May 2010 14:42, Tony Morris <tonymorris@gmail.com> wrote:
We all know that "class (Functor f) => Monad f" is preferable but its absence is a historical mistake. We've all probably tried once:
instance (Functor f) => Monad f where
Do you mean the reverse of this (instance (Monad m) => Functor m where) ?
Yes.
-- Tony Morris http://tmorris.net/
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