Re: [GHC] #11635: Missleading error message when using polymorpic kinds

24 Feb 2016

      #11635: Missleading error message when using polymorpic kinds
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        Reporter:  phadej            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1-rc2
      Resolution:                    |             Keywords:  TypeInType
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 phadej):

 And I found a workaround to make a code compile. It's not usable, but
 that's probably another issue:

 {{{
 {-# LANGUAGE TypeInType, ImpredicativeTypes, KindSignatures,
 ExplicitForAll #-}
 import Data.Kind
 import Data.Proxy
 newtype X (a :: forall k. k -> * ) = X { x :: a Bool -> a (*) }

 -- X { x = \_ -> Proxy :: Proxy (*) }
 {-
 fails with:

     • Couldn't match kind ‘forall k1. k1 -> *’ with ‘forall k. k -> *’
       When matching the kind of ‘Proxy’
     • In the expression: Proxy :: Proxy *
       In the ‘x’ field of a record
       In the expression: X {x = \ _ -> Proxy :: Proxy *}

 -}
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11635#comment:2
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