On 01/04/11 19:48, Ben Millwood wrote:
There's a fair question in whether we want deviation from the default at all (although I think the answer is probably yes). I think it's reasonable that any type that is an instance of Monad be forced to have ap = (<*>), for example, so really the only reason I can see we'd want to be able to override those functions would be for efficiency.
Remember the example Monad implies Functor (fmap = Control.Monad.liftM) Traversable implies Functor (fmap = Data.Traversable.fmapDefault) e.g. [] and Maybe are instances of all these classes. yes, liftM and fmapDefault probably must *do* the same thing[*], but one of those definitions still needs to be picked. [*probably--I'm haven't convinced myself that it's true in all cases of "deepening"-type class hierarchies though--we are here trying to engineer to support all cases of "deepening" hierarchies.] -Isaac