[GHC] #12589: GHC panic with defer-typed-holes

[GHC]

#12589: GHC panic with defer-typed-holes
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        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      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 Iceland_jack):

 Simplified version without any dependencies (''generics-sop''):

 {{{#!hs
 import Data.Proxy

 hcpure :: proxy c -> (forall a. c a => f a) -> h f xs
 hcpure _ _ = undefined

 a = minBound
   & hcpure (Proxy @Bounded)
 }}}

 This is a good use case for #393, because of the rank-2 type we need to
 supply two wildcard arguments.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12589#comment:1>
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