[GHC] #9136: Constant folding in Core could be better

[GHC]

#9136: Constant folding in Core could be better
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        Reporter:  simonpj                  |            Owner:
            Type:  bug                      |           Status:  new
        Priority:  normal                   |        Milestone:
       Component:  Compiler                 |          Version:  7.8.2
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  Runtime performance bug  |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Comment (by simonpj):

 You could do that in `PrelRules` too.  Yes, being able to do it in source
 code would be cool, but it all requires more syntax, a story about what
 predicates are allowed, etc etc, and it is far from obvious where to stop.
 The advantage of `PrelRules` is that you can do anything!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9136#comment:2>
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