[GHC] #12919: Equality not used for substitution

[GHC]

#12919: Equality not used for substitution
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        Reporter:  int-index         |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:
  valid program                      |  typecheck/should_compile/T12919
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 I hate to say so, but I doubt it. Fixing this requires making some
 substantive changes to the flattener (specifically, changing "flattened
 types have flattened kinds" to "flattening does not change a type's
 kind"). Making this change in the presence of tycons with kind
 polymorphism will require some delicate work. It will all add up to more
 time than I have, I'm afraid. Merging the far simpler D3315 and D3316
 patches seems to be hard enough these days. (Though I've finally figured
 out that my compilation server is acting unreliably, taking up more of my
 time than I have to offer. Will continue to work locally to get those
 patches in.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12919#comment:10>
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