[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:  closed
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |             Keywords:  deriving,
      Resolution:  fixed             |  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4402
       Wiki Page:                    |
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Comment (by RyanGlScott):

 So `flatten_args` has been merged into GHC, so in theory, this ticket is
 unblocked now. However, after looking at `flatten_args`, I have no idea
 how it relates to this idea. What I was expected (after reading the
 description in comment:3) was some sort of function of type:

 {{{#!hs
 Type -> Coercion -> Type
 }}}

 Where in the example in comment:3, the `Type` argument would be `S
 (Identity a) x`, the `Coercion` argument would be the newtype axiom `g ::
 Identity a ~R# a`, and the result `Type` would be `S a (x |> g)`. But
 `flatten_args` doesn't look very much like this at all, so I'm plain
 stumped.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14728#comment:15>
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