[GHC] #3851: type family does not get expanded in ghc-6.12.1

[GHC]

#3851: type family does not get expanded in ghc-6.12.1
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    Reporter:  kosmikus                 |        Owner:                           
        Type:  bug                      |       Status:  new                      
    Priority:  normal                   |    Milestone:                           
   Component:  Compiler (Type checker)  |      Version:  6.12.1                   
    Keywords:                           |   Difficulty:                           
          Os:  Unknown/Multiple         |     Testcase:                           
Architecture:  Unknown/Multiple         |      Failure:  GHC rejects valid program
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Comment(by dreixel):

 Note, however, that if we use a data family

 {{{
 data family DF a :: * -> *
 data instance DF () a = D (App (Equ ()) a)

 bar :: DF () () -> ()
 bar (D (App Refl)) = ()
 }}}

 then both 6.10.4 and 6.12.1 fail to compile, and I wouldn't know how to
 write this signature in any other way.

 In any case, the example with type families makes the multirec library
 basically unusable in 6.12. The workaround would require giving type
 signatures which are easily 10 lines long. Is there a milestone for the
 implementation of the new type-inference machinery?

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3851#comment:2>
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