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

[GHC]

#12928: Too easy to trigger CUSK condition using TH
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        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:                    |
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Comment (by int-index):

 But isn't necessary to provide a separate type signature for `fffSym0`! I
 can write it like this using scoped type variables:

 {{{
 fffSym0 (x :: TyFun (Proxy a) ()) = undefined :: Type
 }}}

 and its type is inferred as before.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12928#comment:7>
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