[GHC] #9612: Use functional dependencies to give more specific error messages

[GHC]

#9612: Use functional dependencies to give more specific error messages
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              Reporter:  rwbarton    |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.3
             Component:  Compiler    |         Keywords:
  (Type checker)                     |     Architecture:  Unknown/Multiple
            Resolution:              |       Difficulty:  Unknown
      Operating System:              |       Blocked By:
  Unknown/Multiple                   |  Related Tickets:
       Type of failure:              |
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"1a88f9a4fb373ce52284996212fc23b06848b1c0/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="1a88f9a4fb373ce52284996212fc23b06848b1c0"
 Improve error messages from functional dependencies

 Reponding to Trac #9612:

  * Track the CtOrigin of a Derived equality, arising from a
    functional dependency

  * And report it clearly in the error stream

 This relies on a previous commit, in which I stop dropping Derived
 insolubles on the floor.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9612#comment:4>
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