[GHC] #13026: RFC functions for sums and products

[GHC]

#13026: RFC functions for sums and products
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        Reporter:  Iceland_jack      |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  libraries/base    |              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):

 Here is an interesting one, witnessing the isomorphism between `Sum
 Identity` and
 [https://hackage.haskell.org/package/transformers-0.3.0.0/docs/Control-
 Applicative-Lift.html Control.Applicative.Lift.Lift]

 {{{#!hs
 toLift :: Sum Identity g ~> Lift g
 toLift = \case
   InL (Identity a) -> Pure a
   InR ga           -> Other ga
 }}}

 if it ever gets added to ''base''.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13026#comment:9>
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