[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 simonpj):

 Right.  In ''type signatures'' we look at the type signature '''all by
 itself''', quite '''independent of the definition''', and generalise any
 kind variables.  So when you write
 {{{
 fffSym0 :: TyFun (Proxy a) () -> Type
 }}}
 we'll behave (as you say) as if you wrote:
 {{{
 fffSym0 :: forall k. forall (a:k). TyFun (Proxy a) () -> Type
 }}}
 I agree that this would be reasonable behaviour for a type-level kind
 sinature.  Does everyone agree?

 BUT we don't have separate type-level kind signatures (yet).  If we did,
 yes. But as-is, do we really want to trigger generalisation when (and only
 when) the CUSK conditions are satisfied.  Maybe so...?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12928#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler