[GHC] #8264: Canonical way to prevent manual instances

[GHC]

#8264: Canonical way to prevent manual instances
--------------------------------------------+------------------------------
        Reporter:  nomeata                  |            Owner:
            Type:  task                     |           Status:  new
        Priority:  normal                   |        Milestone:
       Component:  Compiler (Type checker)  |          Version:  7.6.3
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  None/Unknown             |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
--------------------------------------------+------------------------------

Comment (by monoidal):

 I don't know internals, but this mechanism might also work for `(~)` and
 `(<=)` constraints (type-level naturals inequality). Currently they give
 "Malformed instance" error.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8264#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler