[GHC] #13441: Type inference failure in bidirectional pattern synonym and GADT pattern match

[GHC]

#13441: Type inference failure in bidirectional pattern synonym and GADT pattern
match
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms
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:"7c7479d047113a0cbf237c864d403bb638ca0241/ghc"
 7c7479d0/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="7c7479d047113a0cbf237c864d403bb638ca0241"
 Fix explicitly-bidirectional pattern synonyms

 This partly fixes Trac #13441, at least for the explicitly
 bidirectional case.

 See Note [Checking against a pattern signature], the part about
 "Existential type variables".

 Alas, the implicitly-bidirectional case is still not quite right, but
 at least there is a workaround by making it explicitly bidirectional.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13441#comment:2>
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