[GHC] #4347: Asymmetry of (impredicative) instantiation/higher rank types

[GHC]

#4347: Asymmetry of (impredicative) instantiation/higher rank types
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    Reporter:  dolio                    |        Owner:                           
        Type:  bug                      |       Status:  new                      
    Priority:  normal                   |    Milestone:  7.4.1                    
   Component:  Compiler (Type checker)  |      Version:  7.1                      
    Keywords:                           |     Testcase:                           
   Blockedby:                           |   Difficulty:                           
          Os:  Linux                    |     Blocking:                           
Architecture:  x86_64 (amd64)           |      Failure:  GHC rejects valid program
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Comment(by carlhowells):

 Thank you, Simon.  The more I thought about the QML overview (I didn't
 read the full paper), the more I suspected there was an answer like this -
 "It's possible, but in a way I won't guess without reading the paper or
 thinking about it a lot.  And there's probably some syntax that could make
 it easier that I don't know about."

 Now that I see what you did, that does make sense.  I wish the error
 message was a little clearer, though.

 I guess I need to read the QML paper for the details of this system,
 though.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4347#comment:9>
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