[GHC] #14191: Implement Semigroup as a superclass of Monoid Proposal (Phase 2)

[GHC]

#14191: Implement Semigroup as a superclass of Monoid Proposal (Phase 2)
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        Reporter:  hvr               |                Owner:  hvr
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  libraries/base    |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #10365            |  Differential Rev(s):  phab:D3927
       Wiki Page:                    |
  prime:Libraries/Proposals/SemigroupMonoid|
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Comment (by RyanGlScott):

 The SMP is already a rather backwards //in//compatible change as it is (in
 the sense that many libraries are going to be broken until they catch up
 and add `Semigroup` instances), so I don't feel too shaken up about
 changing a `Monoid` constraint to a `Semigroup` one on top of that.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14191#comment:9>
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