[GHC] #10577: Use empty cases where appropriate when deriving instances for empty types

[GHC]

#10577: Use empty cases where appropriate when deriving instances for empty types
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        Reporter:  rwbarton          |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:  deriving
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13117, #7401     |  Differential Rev(s):  Phab:D4047
       Wiki Page:                    |
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Comment (by RyanGlScott):

 I'm not sure if you're asking me to add something here or in the Diff. If
 the latter, are you asking for a test case to see if something like this
 evaluates to `True`?

 {{{#!hs
 {-# LANGUAGE EmptyDataDeriving #-}
 module Main where

 import Data.Function

 data Foo deriving Eq

 foo1 :: Foo
 foo1 = fix id

 foo2 :: Foo
 foo2 = let x = y
            y = x
         in y

 main :: IO ()
 main = print (foo1 == foo2)
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10577#comment:9>
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