[GHC] #13731: DeriveFunctor and friends don't understand type families

[GHC]

#13731: DeriveFunctor and friends don't understand type families
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        Reporter:  spacekitteh       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1-rc2
      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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Comment (by simonpj):

 The error message is terrible.  (Ryan might you look at that?)

 But the program IS wrong.  In Haskell you can't write
 {{{
 f (xs ++ ys) = ...
 }}}
 which pattern-matches on a function call.  And similarly at the type level
 you can't pattern match on a function call, as in `instance Functor (Test
 ListExtension)`.

 Instead write `instance Functor []`. Oh!  We have that instance already;
 so you can just omit it!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13731#comment:1>
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