[GHC] #15622: Generalize `E{0,1,2,3,6,9,12}` from `Data.Fixed`

[GHC]

#15622: Generalize `E{0,1,2,3,6,9,12}` from `Data.Fixed`
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        Reporter:  rockbmb           |                Owner:  rockbmb
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Core Libraries    |              Version:  8.4.3
      Resolution:                    |             Keywords:  base,
                                     |  Data.Fixed
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rockbmb):

 Since no code from Hackage derives instances against these types
 currently, does anyone disagree it is safe to assume no code (published on
 Hackage) will break from this change?

 Projects not uploaded to Hackage or that are closed-source and rely on GHC
 may have issues if they have instances defined for `E0/E1...`, but I do
 not think they will be too great. In these cases, would the addition of
 `FlexibleInstances` be problematic? I do not think so, but that is my
 opinion.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15622#comment:13>
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