[GHC] #12057: TypeFamilyDependencies on Data.Type.Bool's `Not`

[GHC]

#12057: TypeFamilyDependencies on   Data.Type.Bool's `Not`
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        Reporter:  Iceland_jack      |                Owner:  Iceland_jack
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  libraries/base    |              Version:  8.0.1
      Resolution:                    |             Keywords:  TypeFamilies,
                                     |  Injective, newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2268
       Wiki Page:                    |
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Comment (by Iceland_jack):

 Replying to [comment:7 RyanGlScott]:
 > I say "in principle" because although most `Generic` instances (and
 hence `Rep` instances) are derived, a devilish programmer //could//
 handwrite a `Rep` instance that violates injectivity.
 That could be checked if GHC ends up adding support for head-injectivity,
 there may be use cases for an injective `Rep`.

 > Out of curiosity, are there any other type families in `base` besides
 `Not` that can be injective?
 I can sift through `base` and see if there are others, posting them here.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12057#comment:11>
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