[GHC] #11512: An unwritten kind variable is "specified", when it shouldn't be.

29 Jan 2016

      #11512: An unwritten kind variable is "specified", when it shouldn't be.
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           Reporter:  goldfire       |             Owner:  goldfire
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
  TypeApplications                   |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 This fails:

 {{{#!hs
 {-# LANGUAGE PolyKinds, TypeApplications, ScopedTypeVariables #-}

 module Bug where

 import Data.Proxy

 class C a where
   foo :: Proxy a

 bar :: forall a. C a => Proxy a
 bar = foo @a
 }}}

 But it really should work, because the invisible kind variable to class
 `C` should not be available for type application. On the last line, `foo
 @_ @a` works, when you explicitly instantiate the kind variable. Also,
 saying `:t foo` in GHCi shows the specified kind variable.

 Will fix. At some point.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11512
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