[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
-------------------------------------+-------------------------------------
        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  8.2.1
       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:                    |
-------------------------------------+-------------------------------------

Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"b5c81203d047293f54c4e89ac70d505197968cb3/ghc"
 b5c81203/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="b5c81203d047293f54c4e89ac70d505197968cb3"
 Complete the fix for #13441 (pattern synonyms)

 Do not attempt to typecheck both directions of an
 implicitly-bidirectional pattern synonym simultanously,
 as we were before.  Instead, the builder is typechecked
 when we typecheck the code for the builder, which was
 of course happening already, even in both bidirectional
 cases.

 See Note [Checking against a pattern signature], under
 "Existential type variables".
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13441#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler