[GHC] #10733: Improving the error message for type variable ambiguity

[GHC]

#10733: Improving the error message for type variable ambiguity
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        Reporter:  Rufflewind        |                Owner:  kanetw
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1182
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Comment (by Austin Seipp <austin@…>):

 In [changeset:"7b443bb1df8f7f0a6b3124537590aa655a9300cd/ghc"
 7b443bb1/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="7b443bb1df8f7f0a6b3124537590aa655a9300cd"
 Improve error messages for ambiguous type variables

 Improved error messages are only printed when the old message would be
 "No instance for...", since they're not as helpful for "Could not
 deduce..."

 No special test case as error messages are tested by other tests already.

 Signed-off-by: David Kraeutmann <kane at kane.cx>

 Reviewed By: austin, goldfire

 Differential Revision: https://phabricator.haskell.org/D1182

 GHC Trac Issues: #10733
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10733#comment:6>
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