Re: Proposal: Make Semigroup as a superclass of Monoid

On 2015-03-29 at 14:20:33 +0200, Jeremy wrote:

Now that 7.10 is out, I would like to re-propose. The proposed plan is similar to AMP, but less invasive, as (in my subjective experience) user-defined Monoids are much less common than user-defined Monads.

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.

2. GHC >7.12 will define Monoid as a subclass of Semigroup.

+1