[GHC] #9574: GHC Panic: No Skolem Info

[GHC]

#9574: GHC Panic: No Skolem Info
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              Reporter:  ian_mi      |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.9
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by monoidal):

 I reduced the panic to this (to reproduce just run `ghci Bug9574`). It
 makes 7.9 panic but not 7.8, likely by accident though.

 {{{
 {-# LANGUAGE PolyKinds, DataKinds, TypeFamilies, ScopedTypeVariables,
 GADTs, RankNTypes #-}
 module Bug9574 where

 data KProxy (t :: *) = KProxy
 data Proxy p

 class Funct f where
     type Codomain f :: *

 instance Funct ('KProxy :: KProxy o) where
     type Codomain 'KProxy = NatTr (Proxy :: o -> *)

 data NatTr (c :: o -> *) where
     M :: (forall (a :: o). Proxy a) -> NatTr (c :: o -> *)

 p :: forall (c :: o -> *). NatTr c
 p = M t where
     M t = undefined :: Codomain ('KProxy :: KProxy o)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9574#comment:6>
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