[GHC] #14728: Is (GeneralizedNewtypeDeriving + associated type classes) completely bogus?

[GHC]

#14728: Is (GeneralizedNewtypeDeriving + associated type classes) completely bogus?
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |             Keywords:  deriving,
      Resolution:                    |  TypeFamilies
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):

 After talking to goldfire about this, I can answer my earlier question in
 comment:7:

 Replying to [comment:7 RyanGlScott]:
 > Is this blocked (at least partially) on getting your branch merged
 and/or fixing #14729?

 The short answer is: no.

 The long answer is: what goldfire was suggesting in comment:3 was that an
 intrepid GHC hacker could look at the innards of his GHC fork at
 https://github.com/goldfirere/ghc and, conceivably, adapt the logic he
 uses in `TcFlatten.flatten_args` to come up with an algorithm that would
 fix the problem in this ticket. (I had mistakenly though he meant that
 `liftCoSubst` //was// this algorithm, but in fact, it's only one component
 of it.)

 That being said, the performance of `TcFlatten.flatten_args` is apparently
 pretty bad, so adapting it in its current state might not be the wisest
 course of action. In light of this, I think I'll hold off on this idea for
 now and proceed with option (2) in comment:2 as a stopgap solution.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14728#comment:9>
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