[GHC] #11581: TypeError requires UndecidableInstances unnecessarily

[GHC]

#11581: TypeError requires UndecidableInstances unnecessarily
-------------------------------------+-------------------------------------
        Reporter:  rwbarton          |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1-rc2
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:  indexed-
  valid program                      |  types/should_compile/T11581
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by rwbarton):

 Empty and closed. Exactly like it is now except having arity 0 rather than
 2 (as it does currently) or 1 (best I can seem to do currently).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11581#comment:9>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler