[Hugs] #28: Cannot make existential type instance of class with fundep

[Hugs]

#28: Cannot make existential type instance of class with fundep
-------------------------+--------------------------------------------------
 Reporter:  guest        |       Owner:  nobody
     Type:  defect       |      Status:  new   
 Priority:  minor        |   Milestone:        
Component:  type system  |     Version:  200605
 Keywords:               |  
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There seems to be a problem when combining !FunDeps and Existential Types.
 The code below (works on ghci) causes an error:

 - ''ERROR "Existential.hs":8 - Existentially quantified variable escapes
 from pattern !FooObj a''.

 {{{
 class Foo a b | a -> b where foo :: a -> (String,b)

 data FooA = A
 instance Foo FooA String where foo _  = ("tyA","A-specific")

 data FooObj = forall a b. Foo a b => FooObj a
 instance Foo FooObj () where foo (FooObj a) = (fst (foo a),()) -- !!!
 }}}


 best regards, benedikt

-- 
Ticket URL: <http://hackage.haskell.org/trac/hugs/ticket/28>
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