[GHC] #3714: Associated types missing useful functionality

[GHC]

#3714: Associated types missing useful functionality
---------------------------------+------------------------------------------
    Reporter:  simonpj           |        Owner:  chak        
        Type:  bug               |       Status:  new         
    Priority:  normal            |    Milestone:              
   Component:  Compiler          |      Version:  6.10.4      
    Keywords:                    |   Difficulty:              
          Os:  Unknown/Multiple  |     Testcase:              
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown
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 Martijn van Steenbergen pointed out this program:
 {{{
 {-# LANGUAGE TypeFamilies #-}

 module M where

 -- Accepted
 type family T1 f e :: *
 class C1 f where
   op1 :: T1 f e -> Either e a

 -- Rejected
 class C2 f where
   type T2 f e :: *
   op2 :: T2 f e -> Either e a
 }}}
 At the moment (HEAD) the C1/T1 version is accepted but the C2/T2
 declarations are rejected:
 {{{
 TF.hs:12:3: Not in scope: type variable `e'
 }}}
 I think this is just a bug.

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3714>
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