[GHC] #11117: mdo blocks in error messages are shown modified

[GHC]

#11117: mdo blocks in error messages are shown modified
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        Reporter:  nomeata           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  7.8.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 You are dead right ... this is not what GHC usually does.

 But it's harder here.  The renamer re-organises an `mdo` into strongly-
 connected components, and therefore adds `rec` statements.  This message
 comes from the type checker, which now doesn't know the original program.
 Not great. I'm not sure the best way to fix.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11117#comment:1>
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