[GHC] #15711: Kind inference of class variables does not examine associated types

5 Oct 2018

      #15711: Kind inference of class variables does not examine associated types
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           Reporter:  goldfire       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.6.1
           Keywords:  TypeInType     |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 If I say this

 {{{
 {-# LANGUAGE TypeFamilies, PolyKinds, DataKinds #-}

 module Bug where

 class C a where
   type F (x :: Maybe a)
 }}}

 then GHCi says this

 {{{
 *Bug> :k C
 C :: k -> Constraint
 }}}

 That's silly. `C` should have kind `Type -> Constraint`, because the usage
 of `a` in the kind of the associated type constraints `a`'s kind.

 Will fix.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15711
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