[GHC] #12057: TypeFamilyDependencies on GHC.Generic's `Rep`

[GHC]

#12057: TypeFamilyDependencies on GHC.Generic's `Rep`
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        Reporter:  Iceland_jack      |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  libraries/base    |              Version:  8.0.1
      Resolution:                    |             Keywords:  TypeFamilies,
                                     |  Injective
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 RyanGlScott):

 `Rep` definitely isn't injective. Counterexample: `Rep (Proxy Int)` = `Rep
 (Proxy Char)`, but `Int` is not `Char`.

 `Not` can certainly be made injective though, and this would be simple to
 do and useful. Would you care to make a patch for it?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12057#comment:3>
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