[GHC] #14185: Non-local bug reporting around levity polymorphism

[GHC]

#14185: Non-local bug reporting around levity polymorphism
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.3
      Resolution:                    |             Keywords:
                                     |  LevityPolymorphism,
                                     |  TypeErrorMessages
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:"6c19112ece09a098c71faac1f7a58dbb1e63ee71/ghc" 6c19112/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="6c19112ece09a098c71faac1f7a58dbb1e63ee71"
 Build more implications

 The "non-local error" problem in Trac #14185 was due to the
 interaction of constraints from different function definitions.

 This patch makes a start towards fixing it.  It adds
 TcUnify.alwaysBuildImplication to unconditionally build an
 implication in some cases, to keep the constraints from different
 functions separate.

 See the new Note [When to build an implication] in TcUnify.

 But a lot of error messages change, so for now I have set
    alwaysBuildImplication = False

 Result: no operational change at all.  I'll get back to it!
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14185#comment:4>
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