Proposal: Add Foldable1 from 'semigroupoids' to base

[Tony Morris]

* Foldable1 -> Semifoldable
* Bind -> Semimonad
* Apply -> Semiapplicative

What other changes are required?

On Fri, Jun 8, 2018 at 5:20 AM, Edward Kmett <ekmett at gmail.com> wrote:

> I’m generally on board with doing this proposal, but on a pretty slow time
> table. Why? There is an active change I want to make to the API of
> semigroupoids that will require a major version bump and would affect the
> API for Foldable1 among other classes in the library.
>
> The change is more or less the move to calling it Semifoldable, and
> refactoring Bind and Apply into Semimonad and Semiapplicative to enable
> users to find prior literature on the ideas behind them.
>
> This will require a major version bump on the semigroupoids package and
> I’d like to see the dust settle on that before we proceed with anything
> that as it involves over 100 downstream dependencies having to move.
> Fortunately I wrote about half of them. Unfortunately, I’m doing a lot of
> travel for the next couple of months so it may be a bit of a community
> effort to get everything patched over once we decide to pull the trigger.
>
> I prefer to make big API changes far outside of base. They are much more
> expensive to make after things merge in.
>
> -Edward
>
> On Jun 7, 2018, at 9:12 PM, Daniel Cartwright <chessai1996 at gmail.com>
> wrote:
>
> For those of you unfamiliar with 'Foldable1', it is a typeclass for
> nonempty foldable structures, that centres around Semigroup instead of
> Monoid.
> I have made a differential on Phabricator for the change here:
> https://phabricator.haskell.org/D4812
>
> Some discussion at the following links also:
>
> https://ghc.haskell.org/trac/ghc/ticket/13573
>
> https://www.reddit.com/r/haskell/comments/8p531d/ann_
> safefoldable_safe_wrappers_for_nullpartial/
>
> https://github.com/ekmett/semigroupoids/issues/49
>
> Note: foldl1 and foldr1 are currently typeclass methods of 'Foldable' and
> not 'Foldable1', and even though I think they should be, they probably (and
> shouldn't) be removed in this change, though I hope that eventually they
> can be moved to Foldable1.
>
> Foldable1 is also unfortunately named due to the suffix '1' being
> connotated with the conventions surrounded Data.Functor.Classes (Show1,
> Eq1, etc.). If this naming is seen as sufficiently unfortunate/confusing
> because of that, then perhaps the name should be changed to something like
> 'SemiFoldable'. The name change would most likely have to be made in
> 'semigroupoids' first if that is the case.
>
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