i wasnt aware of such guidelines for the libraries list constrained monads/ functors are still an area of study / experimentation, they need experimentation and more community knowledge before they land in base for core type classes On Thu, Jul 27, 2017 at 8:37 PM, David Feuer wrote:

Off-list: Repeating what Eric Mertens said does not contribute to the discussion. Perhaps you can offer an answer to my follow-up question to him.

On Jul 27, 2017 8:26 PM, "Carter Schonwald" wrote:

...

agreed.

this needs to be tested out in a user space lib first.

On Thu, Jul 27, 2017 at 7:35 PM, Eric Mertens wrote:

...

I would prefer to see designs for something like this explored in a separate package before we worried about changing base’s Foldable class.

...

On Jul 27, 2017, at 3:45 PM, David Feuer wrote:

The Foldable class offers the method

elem :: Eq a => a -> t a -> Bool

Unfortunately, this is really awful for sets, hash maps, etc. See https://stackoverflow.com/questions/45361801/implement-an-ol og-n-foldable-elem-for-binary-search-trees-in-haskell#45362110 for an example. We could fix it, kinda:

class Foldable t where type ElemConstr t :: * -> Constraint type ElemConstr t = Eq

elem :: ElemConstr t a => a -> t a -> Bool default elem :: (ElemConstr t ~ Eq, Eq a) => a -> t a -> Bool

One might legitimately complain that such a wild type is ad hoc, but one might counter that complaint by saying that most of Foldable is already ad hoc.

David _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries