On 29 March 2015 at 23:20, Jeremy
The proposal to make Semigroup a superclass of Monoid was discussed a while ago [1], and the conclusion was to "put this off until the dust has settled from the AMP and FT changes".
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 Conrad.