[GHC] #8084: Enabling PolyKinds makes some type errors weird

[GHC]

#8084: Enabling PolyKinds makes some type errors weird
--------------------------------------------+------------------------------
        Reporter:  MartijnVanSteenbergen    |            Owner:
            Type:  bug                      |           Status:  new
        Priority:  normal                   |        Milestone:
       Component:  Compiler (Type checker)  |          Version:  7.6.3
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  None/Unknown             |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
--------------------------------------------+------------------------------

Comment (by MartijnVanSteenbergen):

 Ah, the messages make more sense now. It took me a while to see how to
 read those types.

 So, to make sure I understand everything correctly, the kinds are as
 follows:

 {{{
 Any :: forall k. (k -> *) -> *
 X   :: forall k. k -> *
 Y   :: * -> *
 Z   :: Bool -> *
 }}}

 And whenever a kind has a forall in it, GHC shows how it instantiated that
 kind variable.

 As for preference, I can imagine that having this information is very
 valuable, but I think it's confusing to use notation that is
 indistinguishable from normal type application. So something like `Any {*}
 Y` would help.

 I also think it would help if the User's Guide explained that GHC shows
 this extra information, with Simon's example of when this information is
 needed.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8084#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler