[GHC] #15050: ScopedTypeVariables could allow more programs

[GHC]

#15050: ScopedTypeVariables could allow more programs
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        Reporter:  nomeata           |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nomeata):

 I can get the example from the original ticket to work simply by using
 `TauTv` instead of `SigTv`. But I’m sure that breaks stuff – in particular
 since `SigTv` are also used for type-checking (see
 faec8d358985e5d0bf363bd96f23fe76c9e281f7 and
 8361b2c5a9f7a00f0024f44a43b851998ae41e33) – maybe a separate `KindTv`
 would be cleaner?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15050#comment:12>
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