[GHC] #10978: Anonymous type instances

[GHC]

#10978: Anonymous type instances
-------------------------------------+-------------------------------------
        Reporter:  benjamin.hodgson  |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.8.3
  checker)                           |
      Resolution:                    |             Keywords:
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 nomeata):

 > Because type families are not injective and generative, you cannot
 specify a type family in a class instance head.

 Would it be possible to allow type families in instance heads if they
 reduce to something that is allowed, akin to `TypeSynonymInstances`?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10978#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler