[GHC] #14180: Strange/bad error message binding unboxed type variable

[GHC]

#14180: Strange/bad error message binding unboxed type variable
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.3
       Component:  Compiler (Type    |              Version:  8.3
  checker)                           |
      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 RyanGlScott):

 To motivate why I want this, it's because the
 [http://hackage.haskell.org/package/kind-generics kind-generics] library
 (described in the paper //Generics of All Kinds//) is attempting to come
 up with a uniform representation of both lifted and unlifted types. Due to
 the way `kind-generics` works, we need to implement a type family with
 this shape:

 {{{#!hs
 type family Interpret (t :: Atom d k) (tys :: LoT d) :: k where
 }}}

 Where `k` is the type of the type being interpreted. At the moment, since
 `k :: Type`, `Interpret` is exclusively limited to use with lifted types.
 I'd like to be able to instead say:

 {{{#!hs
 type family Interpret (t :: Atom d (k :: TYPE r)) (tys :: LoT d) :: (k ::
 TYPE r) where
 }}}

 But GHC won't let me do so for the same reasons as in this ticket.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14180#comment:10>
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