[GHC] #10094: Template Haskell cannot represent type wildcards

[GHC]

#10094: Template Haskell cannot represent type wildcards
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              Reporter:  adamgundry  |             Owner:
                  Type:  feature     |            Status:  new
  request                            |         Milestone:
              Priority:  normal      |           Version:  7.10.1-rc1
             Component:  Template    |  Operating System:  Unknown/Multiple
  Haskell                            |   Type of failure:  GHC rejects
              Keywords:              |  valid program
          Architecture:              |        Blocked By:
  Unknown/Multiple                   |   Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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 There does not appear to be a way for Template Haskell code to generate
 partial type signature wildcards. The type quasiquote `[t|_|]` results in
 `Wildcard not allowed`, and use in an expression quasiquote like `[|() ::
 _|]` results in `Exotic form of type not (yet) handled by Template Haskell
 _`.

 It would be useful if TH code could partially constrain the type of the
 expressions it was generating, without needing to determine the type
 completely.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10094>
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