[GHC] #9664: Add identity functor to base

[GHC]

#9664: Add identity functor to base
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              Reporter:  hvr         |            Owner:  ekmett
                  Type:  task        |           Status:  patch
              Priority:  normal      |        Milestone:  7.10.1
             Component:  Core        |          Version:
  Libraries                          |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D313   |
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Comment (by hvr):

 Replying to [comment:5 ross]:
 > Changing to have Data.Functor.Class import Data.Functor.Identity reduces
 the ifdefs.

 Sure, I can easily change that (at the cost of some minor code
 duplication)

 > Ideally I'd like to avoid a release with conditional exports - is there
 any way to detect a GHC bootstrap build?

 As for this I'm not sure how that helps here. Assuming we have a way of
 setting a Cabal flag when we're bootstrapping GHC (i.e. building stage 1),
 how would this improve the situation of having the `Data.Functor.Identity`
 module conditionally exposed (which now would be depending on that Cabal
 flag setting rather than predicating on `impl(ghc>=7.9)`)?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9664#comment:6>
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