[GHC] #16372: GHC can't constant fold even basic power (^) applications for Int (and others?)

[GHC]

#16372: GHC can't constant fold even basic power (^) applications for Int (and
others?)
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        Reporter:  Fuuzetsu          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      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 hsyl20):

 > Then we could add `(^)` as a method of Num a, change its type to be `(^)
 :: a -> a -> a` and use the appropriate primitives (or fall back to the
 generic implementation otherwise). Exactly like we do for other
 primitives.

 Hmm in fact it won't work for non integral `Num` types (e.g., Double)...
 Maybe we could add another function (`ipow`?) to `Integral` instead and
 add rules to convert `(^)` into `ipow` for known cases.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16372#comment:3>
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