[GHC] #12124: Ambiguous type variable: it's a red herring!

[GHC]

#12124: Ambiguous type variable: it's a red herring!
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        Reporter:  drb226            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      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:"465c6c5d15f8fb54afb78408f3a79e75e74d2cd4/ghc" 465c6c5/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="465c6c5d15f8fb54afb78408f3a79e75e74d2cd4"
 Improve error handling in TcRnMonad

 See Note [Constraints and errors] in TcRnMonad.  This
 patch fixes Trac #12124 in quite a neat way.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12124#comment:4>
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