[GHC] #11456: Type application and :set +c command cause panic

[GHC]

#11456: Type application and :set +c command cause panic
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        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  TypeApplications GHCi
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 rwbarton):

 Specifically, leave `Parser.y` unchanged, but at the end of parsing,
 convert all `HsApp e (HsType t)` to `HsTypeApp e t` (modulo locations,
 etc.) Then there are no invariants of the form "`HsType` can appear only
 within `HsApp`", just ones of the form "the output of [stage X] cannot
 contain [constructor Y]".

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11456#comment:4>
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