[GHC] #9167: Associated type is accepted even without mentioning class parameters

[GHC]

#9167: Associated type is accepted even without mentioning class parameters
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       Reporter:  goldfire          |             Owner:
           Type:  bug               |            Status:  new
       Priority:  low               |         Milestone:
      Component:  Compiler          |           Version:  7.8.2
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 The following module is accepted:

 {{{
 {-# LANGUAGE TypeFamilies #-}

 module Bug where

 class C a where
   type F b
 }}}

 Note that the associate type family `F` does not mention the class
 variable `a`. Because associated type families are somewhat thin sugar
 over non-associated type families, I doubt this causes any great disaster
 anywhere, but it should probably be fixed.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9167>
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