[GHC] #10119: Class methods must always mention the class variable

[GHC]

#10119: Class methods must always mention the class variable
-------------------------------------+-------------------------------------
              Reporter:  thomie      |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:  7.12.1
             Component:  Compiler    |           Version:  7.10.1-rc2
  (Type checker)                     |  Operating System:  Unknown/Multiple
              Keywords:              |   Type of failure:  None/Unknown
          Architecture:              |        Blocked By:
  Unknown/Multiple                   |   Related Tickets:  #7854, #10118
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
 As mentioned in comment:9:ticket:7854, GHC wrongfully accepts the
 following program. It should reject it, because `op` doesn't mention any
 type variables of `Foo` (the method context doesn't count).

 {{{#!hs
 module ShouldFail where
 class Foo a where
   op :: Eq a => Int
 }}}

 I'm working on it.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10119>
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