[GHC] #9103: hackage's type-level-0.2.4 fails to compile

[GHC]

#9103: hackage's type-level-0.2.4 fails to compile
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        Reporter:  slyfox                     |            Owner:
            Type:  bug                        |           Status:  closed
        Priority:  normal                     |        Milestone:
       Component:  Compiler (Type checker)    |          Version:  7.8.2
      Resolution:  invalid                    |         Keywords:
Operating System:  Unknown/Multiple           |     Architecture:
 Type of failure:  GHC rejects valid program  |  Unknown/Multiple
       Test Case:                             |       Difficulty:  Unknown
        Blocking:                             |       Blocked By:
                                              |  Related Tickets:  #8634
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Changes (by rwbarton):

 * status:  new => closed
 * resolution:   => invalid
 * related:   => #8634


Comment:

 The error looks correct to me.

 {{{
 class Succ' xh xl yh yl yz | xh xl -> yh yl yz, yh yl yz -> xh xl
 instance Failure (PredecessorOfZeroError x) => Succ' (x,x) (x,x) D0 D0
 True
 }}}

 The functional dependency `yh yl yz -> xh xl` is violated because `D0 D0
 True` do not determine `(x,x) (x,x)`: `x` is free. An instance of #8634.
 I'm going to mark this ticket as invalid (since it seems to me that you
 are considering this as a regression rather than a feature request), but
 see that ticket and its related tickets for ongoing discussion.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9103#comment:1>
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