[GHC] #11255: Expected kind ‘k0’, but has kind ‘(forall k. k, forall k. k)’

18 Dec 2015


      #11255: Expected kind ‘k0’, but has kind ‘(forall k. k, forall k. k)’
-------------------------------------+-------------------------------------
           Reporter:  atnnn          |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.11
  (Type checker)                     |
           Keywords:                 |  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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 The following code works in GHC 7.10:

 {{{#!hs
 {-# LANGUAGE TypeFamilies, PolyKinds, DataKinds, UndecidableInstances #-}

 type family Default :: k
 type instance Default = '(Default, Default)
 }}}

 But fails in HEAD with:

 {{{
 Expected kind ‘k0’, but ‘'(Default, Default)’ has kind ‘(forall k. k,
 forall k. k)’
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11255
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