[GHC] #13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification

[GHC]

#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and
ExistentialQuantification
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        Reporter:  ljli              |                Owner:  simonmar
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.3
       Component:  Compiler          |              Version:  8.1
      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 Simon Peyton Jones <simonpj@…>):

 In [changeset:"254bc3357b0de673b7873f1c4cf5dfc26d0bb5f2/ghc" 254bc33/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="254bc3357b0de673b7873f1c4cf5dfc26d0bb5f2"
 A much nicer solution for typechecking ApplicativeDo

 This patch improves the code for TcMatches.tcApplicativeStmts;
 see the suggestion in Trac #13242 comment:9.

 I now use (mapM goArg args) rather than a CPS-style fold.  The
 result is less code, easier to understand, and automatically
 fixes the original problem in Trac #13242.

 See Note [ApplicativeDo and constraints].
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13242#comment:14>
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