[GHC] #12018: Equality constraint not available in pattern type signature (GADTs/ScopedTypeVariables)

[GHC]

#12018: Equality constraint not available in pattern type signature
(GADTs/ScopedTypeVariables)
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  lowest            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.10.3
  checker)                           |             Keywords:  GADTs,
      Resolution:                    |  ScopedTypeVariables
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 Iceland_jack):

 I think this would largely be solved by #11350,

 {{{#!hs
 eval (ArrIx @_ @elt arr index) = do
   ...
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12018#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler