[GHC] #644: Non-exhaustive patterns in function zip_ty_env

[GHC]

#644: Non-exhaustive patterns in function zip_ty_env
----------------------------------------+-----------------------------------
    Reporter:  simonmar                 |        Owner:         
        Type:  bug                      |       Status:  new    
    Priority:  normal                   |    Milestone:  6.4.2  
   Component:  Compiler (Type checker)  |      Version:  6.4.1  
    Severity:  normal                   |     Keywords:         
          Os:  Unknown                  |   Difficulty:  Unknown
Architecture:  Unknown                  |  
----------------------------------------+-----------------------------------
The following code:

 {{{
 data T a where
     P :: L1 -> L2
 data L1 = L1
 data L2 = L2
 }}}

 Produces this panic:

 {{{
 bug.hs:1:0:
     Data constructor `P' returns type `L2' instead of its parent type
     When checking the data constructor:ghc-6.4.1: panic! (the `impossible'
 happened, GHC version 6.4.1):
         types/Type.lhs:(1107,0)-(1108,77): Non-exhaustive patterns in
 function zip_ty_env
 }}}

-- 
Ticket URL: <http://cvs.haskell.org/trac/ghc/ticket/644>
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