[GHC] #13689: Data.Either doesn't export INLINABLE short functions like "rights"

[GHC]

#13689: Data.Either doesn't export INLINABLE short functions like "rights"
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        Reporter:  varosi            |                Owner:  (none)
            Type:  bug               |               Status:  infoneeded
        Priority:  normal            |            Milestone:
       Component:  Core Libraries    |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect API     |  Unknown/Multiple
  annotation                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nomeata):

 `INLINEABLE` might be reasonable. Isn’t it the case that the unfolding
 stored in the interface will be the un-optimized one (i.e. not the large
 thing visible up there?)

 Or is the large code directly the result of the desugared list
 comprehension (instead of applying rules to the resulting code)?

 > Yes, we could give lefts and rights the same treatment that we give
 filter and give it a "naive" definition, alongside some fusible
 definitions with rules to map one to the other, but I think this is a lot
 of complexity for little pay-off.

 Probably not worth it. `lefts` and `rights` are already defined in terms
 of fusable things (list comprehensions) – this is different for `filter`,
 which has a recursive definition.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13689#comment:9>
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