[GHC] #7642: Nullary type classes

[GHC]

#7642: Nullary type classes
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Reporter:  shachaf           |          Owner:                         
    Type:  feature request   |         Status:  new                    
Priority:  normal            |      Component:  Compiler (Type checker)
 Version:  7.6.1             |       Keywords:                         
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple       
 Failure:  None/Unknown      |      Blockedby:                         
Blocking:                    |        Related:                         
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Comment(by monoidal):

 I strongly support this feature, but another change is needed.

 {{{
 {-# LANGUAGE MultiParamTypeClasses #-}
 class A where
   f :: a -> a


 H.hs:2:1:
     The class method `f'
     mentions none of the type variables of the class A
     When checking the class method: f :: forall a. a -> a
     In the class declaration for `A'
 Failed, modules loaded: none.
 }}}

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7642#comment:1>
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