[GHC] #13650: Implement KPush in types

[GHC]

#13650: Implement KPush in types
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        Reporter:  goldfire          |                Owner:  goldfire
            Type:  task              |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:
      Resolution:                    |             Keywords:
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 goldfire):

 One wrinkle (at least until #11715 is fixed): which `eqType` do we wish to
 respect here? `eqType` or `tcEqType`? I think it might be best to wait
 until after #11715. Or it's possible that it doesn't matter which `eqType`
 we're thinking of.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13650#comment:2>
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