Re: [GHC] #14038: TypeApplications regression in GHC HEAD: ‘p0’ is untouchable inside the constraints: ()

[GHC]

#14038: TypeApplications regression in GHC HEAD: ‘p0’ is untouchable inside the
constraints: ()
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.3
  checker)                           |             Keywords:
      Resolution:                    |  TypeApplications
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:  14119             |             Blocking:
 Related Tickets:  #13877            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 comment:6 says:

 > The problem is that the App instance for (:~>) gets type-checked with a
 coercion in its patterns

 Can you boil this out into a simple case?  I'm lost.

 >  Have TcHsType proceed normally, but rip the coercions out after-the-
 fact.

 That's what happens in Rules.  See `DsBinds.decomposeRuleLhs`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14038#comment:12>
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