[GHC] #11719: Cannot use higher-rank kinds with type families

[GHC]

#11719: Cannot use higher-rank kinds with type families
-------------------------------------+-------------------------------------
        Reporter:  ocharles          |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc2
  checker)                           |
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:
  valid program                      |  dependent/should_compile/T11719
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * status:  merge => closed
 * failure:  None/Unknown => GHC rejects valid program
 * resolution:   => fixed
 * milestone:   => 8.0.1


@@ -7,1 +7,1 @@
- {{{
+ {{{#!hs

New description:

 This ticket came out of a discussion with Richard in this mailing list
 post: https://mail.haskell.org/pipermail/haskell-
 cafe/2016-March/123462.html

 Here's the code that should work, but doesn't:

 {{{#!hs
 import Data.Kind

 data TyFun :: * -> * -> *
 type a ~> b = TyFun a b -> *

 type family (f :: a ~> b) @@ (x :: a) :: b

 data Null a = Nullable a | NotNullable a

 type family ((f :: b ~> c) ∘ (g :: a ~> b)) (x :: a) :: c where
   (f ∘ g) x = f @@ (g @@ x)

 type family BaseType (k :: forall a. a ~> Type) (x :: b) :: Type where
 -- this fails :(
 --  BaseType k x = (@@) k x
 }}}

--

Comment:

 Merged as bae60f654ac5d99834818da9c50ad4bee54c334e.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11719#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler