On Tue, 2011-01-04 at 13:49 +0100, Gábor Lehel wrote:
2) Make 'join' a method of Monad.
Why?
Of course I'm only a sample size of one, but I find join a lot easier to think about and implement than (>>=). Even trying to look at it objectively and factor out my own potential idiosyncracies, it's obvious that it only has one argument to (>>=)'s two, and the type signature looks a lot more straightforward any way I slice it. I was very glad to see this proposal to make it possible to define a Monad using return (pure), fmap, and join, rather than return and (>>=).
I also recall reading somewhere that mathematically speaking join is the more significant operation but I'll leave that to the experts.
+1. I also find join easier. This particular change can be done right now without breaking anything I believe [even if whole proposal is rejected]: class Monad m where return :: a -> m a (>>=) :: m a -> (a -> m b) -> m b (>>) :: m a -> m b -> m b join :: m (m a) -> m a join = (>>= id) mkBind :: Monad m => ((a -> b) -> m a -> m b) -> m a -> (a -> m b) -> m b mkBind map mv mf = join (map mf mv) ... instance Monad m where join = ... return = ... (>>=) = mkBind fmap However with this proposal it is even nicer (no need for mkBind). Regards