Re: [GHC] #14000: Out of scope errors with type families do not mention scope

28 Jul 2017

      #14000: Out of scope errors with type families do not mention scope
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        Reporter:  EyalLotem         |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones ):

 In [changeset:"452755de717fad5d8fbfc6330cb42a3335c8912d/ghc"
 452755de/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="452755de717fad5d8fbfc6330cb42a3335c8912d"
 Do not discard insolubles in implications

 Trac #14000 showed up two errors

 * In TcRnTypes.dropInsolubles we dropped all implications, which
   might contain the very insolubles we wanted to keep.  This was
   an outright error, and is why the out-of-scope error was actually
   lost altogether in Trac #14000

 * In TcSimplify.simplifyInfer, if there are definite (insoluble)
   errors, it's better to suppress the following ambiguity test,
   because the type may be bogus anyway.  See TcSimplify
   Note [Quantification with errors].  This fix seems a bit clunky,
   but it'll do for now.
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14000#comment:6
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