[GHC] #1723: type unsafety with type family + GADT

[GHC]

#1723: type unsafety with type family + GADT
--------------------------------------+-------------------------------------
  Reporter:  zunino at di.unipi.it       |          Owner:         
      Type:  bug                      |         Status:  new    
  Priority:  normal                   |      Milestone:         
 Component:  Compiler (Type checker)  |        Version:  6.8    
  Severity:  major                    |       Keywords:         
Difficulty:  Unknown                  |             Os:  Unknown
  Testcase:                           |   Architecture:  Unknown
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Here's ''unsafeCoerce'':
 {{{
 type family Const a
 type instance Const a = ()

 data T a where T :: a -> T (Const a)

 coerce :: forall a b . a -> b
 coerce x = case T x :: T (Const b) of
            T y -> y
 }}}
 Tested with GHC 6.9.20070918

 Maybe, see also #345

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1723>
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