[GHC] #12928: Too easy to trigger CUSK condition using TH

[GHC]

#12928: Too easy to trigger CUSK condition using TH
-------------------------------------+-------------------------------------
        Reporter:  int-index         |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  high              |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             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:                    |
-------------------------------------+-------------------------------------

Comment (by int-index):

 Replying to [comment:3 simonpj]:
 >
 > We do!  It's called a type signature.
 >

 It doesn't sound right. In a type signature, I can omit polymorphic kinds.
 In a CUSK, I cannot.

 The example in the ticket defines a method `fff` which has a type
 signature, but `a` is kind-polymorphic:

 {{{
   class Cls a  where
     fff :: Proxy a -> ()
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12928#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler