foldl1 for NonEmpty

[andrewthad]

I think that it would be good to add foldl1 to NonEmpty, especially because we can actually write a safe version of it:

nonEmptyFoldl1 :: (a -> a -> a) -> NonEmpty a -> a
nonEmptyFoldl1 g (a :| as) = List.foldl g a as

The same can be done for foldr1. Although at this point in time, it may make more sense to add this to base-4.9 instead of semigroups.

[andrewthad]

Also, having append would be nice.

[tomjaguarpaw]

+1 I've just noticed that append is missing, too.

[RyanGlScott]

Are Data.Foldable.{foldl1,foldr1} and Data.Semigroup.<> not sufficient?

[tomjaguarpaw]

I thought there'd be a catch! Yes, they're sufficient but should be documented as such. Having no reference to "append" in the Haddock is somewhat disconcerting.

[RyanGlScott]

That sounds reasonable. But since Data.List.NonEmpty is in base now, make sure any changes to its documentation also get merged into base as well.

[ekmett]

Any changes here will be made to simply track base. As a result if you want such a function I recommend you file it as a proposal to libraries@haskell.org, so we can get it into base. Any changes made to base will be mirrored here for older GHC versions.