[GHC] #393: functions without implementations

[GHC]

#393: functions without implementations
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        Reporter:  c_maeder          |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  ⊥
       Component:  Compiler (Type    |              Version:  None
  checker)                           |
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Iceland_jack):

 Should also work for methods. This currently fails:

 {{{#!hs
 class FFunctor p where
   ffmap :: (forall x. f x -> g x) -> (p f -> p g)

 instance FFunctor (TList l) where
   ffmap :: (forall x. f x -> g x) -> (TList l f -> TList l g)
   ffmap = undefined
 }}}

 I would like

 {{{#!hs
 class FFunctor p where
   ffmap :: (forall x. f x -> g x) -> (p f -> p g)

 instance FFunctor (TList l) where
   ffmap :: (forall x. f x -> g x) -> (TList l f -> TList l g)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/393#comment:33>
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