On Sun, 29 Mar 2015, Jeremy wrote:
1. GHC 7.12 will include Semigroup and NonEmpty in base. All Monoid instances, and anything else which forms a Semigroup, will have a Semigroup instance. GHC will issue a warning when it encounters an instance of Monoid which is not an instance of Semigroup.
Good news! Btw. in my package 'non-empty' I use a more general type: NonEmpty f a = Cons a (f a) It allows you to create non-empty Sequences etc. and lists with at least two elements (NonEmpty (NonEmpty []) a). However, inclusion of this type in base or replacing the NonEmpty type from "semigroups" is not necessary, since the more general type can stay in the "non-empty" package and get an Semigroup instance there.
The rationale for this change is:
3. NonEmpty is often redefined by beginners (or those who don't think it's worth having an extra dependency for).
And it is often implemented in unnecessarily complicated ways using GADTs or phantom types.