[GHC] #9984: Show, Read, Eq, Ord instances for Control.Applicative.Const

[GHC]

#9984: Show, Read, Eq, Ord instances for Control.Applicative.Const
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        Reporter:  fumieval          |                   Owner:
            Type:  feature request   |                  Status:  patch
        Priority:  low               |               Milestone:  7.10.1
       Component:  libraries/base    |                 Version:  7.8.4
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:  Phab:D619
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Comment (by Herbert Valerio Riedel <hvr@…>):

 In [changeset:"c71fb84b8c9ec9c1e279df8c75ceb8a537801aa1/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="c71fb84b8c9ec9c1e279df8c75ceb8a537801aa1"
 Add Eq, Ord, Show, and Read instances for Const

 As suggested in

 https://www.haskell.org/pipermail/libraries/2013-October/021531.html

 this adds the following instances

  - `Show a => Show (Const a b)`
  - `Read a => Read (Const a b)`
  - `Eq a   => Eq   (Const a b)`
  - `Ord a  => Ord  (Const a b)`

 The Read/Show instances are defined in such a way as if `Const` was
 defined
 without record-syntax (i.e. as `newtype Const a b = Const a`)

 Addresses #9984

 Reviewed By: ekmett

 Differential Revision: https://phabricator.haskell.org/D619
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9984#comment:6>
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