David Feuer wrote:
filterM :: (Monad m) => (a -> m Bool) -> [a] -> m [a] We could change this to filterM :: (Applicative f) => (a -> f Bool) -> [a] -> f [a]
Following the usual conventions, that should be filterA. And I'm not sure where it should go. We could also generalize the list parameter to a Foldable and put it in Data.Foldable, but I don't think that would be very useful, since in the end it anyway returns a list. We could add a new "Filterable" class, but that's also probably not too useful for anything not list-like. For example, Data.Tree has two useful filters, filterGraft and filterPrune. So maybe it should go in Control.Applicative? Not very satisfying. Any ideas? As for the fate of the name filterM: Personally, I would want filterM to remain a convenient type-specialized version for monads. But recent madness would turn it into yet another unsightly overly polymorphic namespace wasting synonym for filterA. Thanks, Yitz