On Wed, 2008-05-28 at 11:11 +0100, Conor McBride wrote:
Ross Paterson wrote:
Several functions on containers used to have types like lookup :: (Ord k) => k -> Map k a -> Maybe a but these were generalized to lookup :: (Monad m, Ord k) => k -> Map k a -> m a The proposal is to change these signatures back, specializing them to Maybe.
I'm all for Maybe in the question Monad VS Maybe.
Me too. (+1) for Ross's proposal.
If we need any more (+1) votes you can count mine.
Also, it's not entirely clear whether MonadZero is the most general abstraction. Is ApplicativeZero better? Or something else?
Maybe is the most general abstraction. Requiring (>>=), or even (<*>) seems excessive. What we need is "any f with zero and return", so why not pick the canonical, initial, inductively defined such thing?
Good. I like that argument. As others have pointed out, it's easy to lift maybe into something else when that's needed. maybe :: a -> (b -> a) -> Maybe b -> a Duncan