[GHC] #11700: pattern match bug

[GHC]

#11700: pattern match bug
-------------------------------------+-------------------------------------
        Reporter:  TobyGoodwin       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  https://github.com/TobyGoodwin/odd-
                                     |  ghc-pattern-bug
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by TobyGoodwin):

 Fantastic work thomie! Thanks so much for this.

 That appears to be standalone to me, no extra packages needed. Copy and
 paste that code into `T11700.hs`, run `ghc T11700.hs` and you get the
 bogus error. Works for me with ghc-7.10.3 and no `~/.ghc` or `~/.cabal`.
 And as thomie says, removing the `TypeFamilies` extension makes the
 problem go away.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11700#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler