[GHC] #11450: Associated types at wrong type in instance

[GHC]

#11450: Associated types at wrong type in instance
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        Reporter:  simonpj           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by simonpj:

Old description:

> Consider
> {{{
> class C x where
>   type T x
>
> instance C (Either a b) where
>   type T (Either b a) = b -> a
> }}}
> This is bogus, because the equation for `T` has the parameters to
> `Either` reversed.

New description:

 Consider
 {{{
 class C x where
   type T x

 instance C (Either a b) where
   type T (Either b a) = b -> a
 }}}
 This is bogus, because the equation for `T` has the parameters to `Either`
 reversed.  But GHC 8.0 RC1 (and master) allow it.

--

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11450#comment:1>
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