[GHC] #10755: Add `MonadPlus IO` and `Alternative IO` instances

[GHC]

#10755: Add `MonadPlus IO` and `Alternative IO` instances
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        Reporter:  hvr               |                   Owner:
            Type:  task              |                  Status:  patch
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Core Libraries    |                 Version:
      Resolution:                    |                Keywords:  report-
                                     |  impact
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D1148
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Changes (by RyanGlScott):

 * cc: ross (added)


Comment:

 While I don't want to cause unnecessary pain for users, I have to wonder
 about the placement of the instances in `transformers`. Currebtly, they're
 located in `Control.Monad.Trans.Error`, which has been deprecated for a
 while. If users want to backport these new `IO` instances in their code,
 they'll have to reach for a module which GHC will warn is deprecated,
 which doesn't feel satisfying.

 Perhaps we could move the orphan instances to a different module in
 `transformers`, reexport it from `Control.Monad.Trans.Error`, and tell
 users to use the new module from here on out for conpatibility purposes?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10755#comment:9>
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