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
_______________________________________________
Haskell-prime mailing list
Haskell-prime@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-prime
