[GHC] #10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1)

[GHC]

#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1)
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        Reporter:  gidyn             |                Owner:  quchen
            Type:  feature request   |               Status:  patch
        Priority:  high              |            Milestone:  8.0.1
       Component:  libraries/base    |              Version:  7.10.1
      Resolution:                    |             Keywords:  report-impact
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1284
       Wiki Page:                    |
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Comment (by ekmett):

 @nomeata:

 FWIW- the implementation in `semigroups` was crafted by mixing and
 matching parts between the 2-3 implementations of non-empty lists at the
 time. The skeleton of it was build mostly by raiding the `NonEmptyList`
 package for parts with permission of the owners. AFAIK, Tony has
 deprecated his `NonEmptyList` package in favor of the one in `semigroups`
 (hence the lack of updates in the last 5 years -- this changeover predated
 having any deprecation mechanism on hackage.)

 Robin Kay's `NonEmpty` package is just a data type with no instances and
 no methods, also 6 years old.

 Cardinality also hasn't seen a patch in 6 years. Remarkably it still
 builds, because it too simply provides no instances.

 `MinLen` requires a ton of type system extensions.

 Out of the things that are suitable to consider as a `base`-ready encoding
 of a non-empty list, only Henning's `Data.NonEmpty` is actively
 maintained, and it tackles a more general problem, and brings with it a
 dozen different ad hoc classes for inserts and the like.

 So if you're hunting for materials to use to rebuild the bikeshed
 completely, I'd say out of the packages on hackage today, that is the only
 real source of lumber.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10365#comment:37>
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