On 05/01/2015 at 11:53:11 -0500, Mario Blažević wrote:
On 14-12-30 12:34 PM, David Feuer wrote:
I realized just now that we can actually make the type a little bit more general still, interpreting `filterM` for lists as being an applicative filter *producing* lists:
filterM :: (Applicative f, Foldable t) => (a -> f Bool) -> t a -> f [a]
I'm +1 on the more limited generalization proposal, but not on this one. I've been feeling for a while that we need a subclass of Traversable to generalize functions like filter, mapMaybe, and partition (potentially span, splitAt and others as well). If you call this missing class Filterable, the properly-generalized signature would be
filterM :: (Applicative f, Filterable t) => (a -> f Bool) -> t a -> f (t a)
https://hackage.haskell.org/package/witherable Interesting name choice...