[GHC] #12708: RFC: Representation polymorphic Num

[GHC]

#12708: RFC: Representation polymorphic Num
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        Reporter:  Iceland_jack      |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Core Libraries    |              Version:  8.0.1
      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 Iceland_jack):

 With the upcoming `UnboxedSums`

 {{{#!hs
 instance (Eq a, Eq b) => Eq (# a | b #) where
   (==) :: (# a | b #) -> (# a | b #) -> Bool
   (# a | #) == (# a' | #) = a == a'
   (# | b #) == (# | b' #) = b == b'
   _         == _          = False
 }}}

 In GHCi, version 8.1.20160930 it seems like you cannot partially apply
 unboxed sums `(# | #)` so I can't write

 {{{#!hs
 instance Functor     ((# | #) a)
 instance Applicative ((# | #) a)
 instance Foldable    ((# | #) a)
 ...
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12708#comment:9>
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