[GHC] #10483: Refactor HsForAllTy

[GHC]

#10483: Refactor HsForAllTy
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              Reporter:  simonpj     |             Owner:
                  Type:  task        |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.1
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 I got sucked into refactoring `HsForAllTy`, like this:
 {{{
 data HsType name
  = HsForAllTy (HsForAll name) (LHsType name)
  | ...

 data HsForAll name      -- The quantifiers of a HsForAllTy
   = HSF { hsf_flag :: HsExplicitFlag
         , hsf_extra :: Maybe SrcSpan
         , hsf_qtvs :: LHsTyVarBndrs name
         , hsf_ctxt :: LHsContext name
     }
 }}}
 This makes a number of functions neater, as well as naming the fields of a
 troublesomely-high-arity data constructor.

 This ticket is here to track progress.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10483>
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