[GHC] #7393: GHC cannot solve functional dependency

[GHC]

#7393: GHC cannot solve functional dependency
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  Reporter:  Khudyakov                  |          Owner:                  
      Type:  bug                        |         Status:  closed          
  Priority:  normal                     |      Milestone:                  
 Component:  Compiler                   |        Version:  7.6.1           
Resolution:  invalid                    |       Keywords:                  
        Os:  Unknown/Multiple           |   Architecture:  Unknown/Multiple
   Failure:  GHC rejects valid program  |     Difficulty:  Unknown         
  Testcase:                             |      Blockedby:                  
  Blocking:                             |        Related:                  
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Changes (by simonpj):

  * status:  new => closed
  * difficulty:  => Unknown
  * resolution:  => invalid


Comment:

 I'm afraid functional dependencies don't work like that.  Type families
 do.  (This is one of the reasons I prefer type families.)

 You might try something like this
 {{{
 class TyPairs (xs :: [*]) where
   type Ys xs :: [*]
 }}}
 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7393#comment:1>
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