#7451: Constraint and * should not be distinct in FC
---------------------------------+------------------------------------------
    Reporter:  simonpj           |       Owner:                  
        Type:  bug               |      Status:  new             
    Priority:  high              |   Milestone:                  
   Component:  Compiler          |     Version:  7.7             
    Keywords:                    |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
  Difficulty:  Unknown           |    Testcase:                  
   Blockedby:                    |    Blocking:                  
     Related:                    |  
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 With GHC 7.7 this program
 {{{
 class B a where
     b :: a

 newtype Additive a = Additive a

 instance B a => B (Additive a) where
    b = Additive b
 }}}
 produces a Core Lint error:
 {{{
 *** Core Lint errors : in result of Simplifier ***
 {-# LINE 8 "T6117.hs #-}: Warning:
     [RHS of T6117.$fBAdditive :: forall a_aeG.
                                  T6117.B a_aeG =>
                                  T6117.B (T6117.Additive a_aeG)]
     Bad axiom application (check_ki2 Sym
                                        (T6117.NTCo:B (T6117.NTCo:Additive
 <a_XeN>))
                                      Constraint
                                      a_aeF
                                      *)
       T6117.NTCo:B (Sym (T6117.NTCo:B (T6117.NTCo:Additive <a_XeN>)))
 }}}
 The reason is that while kinds `Constraint` and `*` should be distinct so
 far as the type inference engine is concerned, they should not be
 distinguished in Core, ie System FC.

 This ticket is culled from #6117, which was really about something else.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7451>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler

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