Re: [GHC] #13761: Can't create poly-kinded GADT with TypeInType enabled, but can without

28 May 2017

      #13761: Can't create poly-kinded GADT with TypeInType enabled, but can without
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Another workaround is to explicitly quantify the kind like so:

 {{{#!hs
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE KindSignatures #-}
 {-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TypeInType #-}
 module Works2 where

 import Data.Kind

 data T :: forall (k :: Type). k -> Type where
   MkT :: T Int
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13761#comment:1
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