[GHC] #1624: internal error caused by adding an instance to a type class with a functional dependency and a default method

[GHC]

#1624: internal error caused by adding an instance to a type class with a
functional dependency and a default method
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    Reporter:  int-e                    |        Owner:  simonpj
        Type:  bug                      |       Status:  new    
    Priority:  normal                   |    Milestone:  6.10   
   Component:  Compiler (Type checker)  |      Version:  6.7    
    Severity:  minor                    |   Resolution:         
    Keywords:                           |   Difficulty:  Unknown
          Os:  Linux                    |     Testcase:         
Architecture:  x86                      |  
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Comment (by int-e):

 ''"GHC rejects this because there is no translation into System F."''

 Too bad. I was afraid that you would say this or something similar. Is
 this particular case explained in any paper?

 Is there any chance that the above code fragments will ever work in ghc? I
 triggered the second two variations while trying to implement a generic
 trie, and sometimes I had to change type signatures after modifying a
 (seemingly) unrelated implementation detail. But of course it's just a
 minor inconvenience, and not worth  giving up a sound basis for the type
 system.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1624>
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