[GHC] #11142: Type-level skolem capture leads to core lint error

[GHC]

#11142: Type-level skolem capture leads to core lint error
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        Reporter:  goldfire          |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  7.10.2
  checker)                           |
      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 simonpj):

 Also see this Note in `TcHsType`:
 {{{
 Note [Kind generalisation]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 We do kind generalisation only at the outer level of a type signature.
 For example, consider
   T :: forall k. k -> *
   f :: (forall a. T a -> Int) -> Int
 When kind-checking f's type signature we generalise the kind at
 the outermost level, thus:
   f1 :: forall k. (forall (a:k). T k a -> Int) -> Int  -- YES!
 and *not* at the inner forall:
   f2 :: (forall k. forall (a:k). T k a -> Int) -> Int  -- NO!
 Reason: same as for HM inference on value level declarations,
 we want to infer the most general type.  The f2 type signature
 would be *less applicable* than f1, because it requires a more
 polymorphic argument.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11142#comment:4>
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