[GHC] #9638: Speed up Data.Char.isDigit

[GHC]

#9638: Speed up Data.Char.isDigit
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              Reporter:  dfeuer      |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:  7.10.1
              Priority:  normal      |          Version:  7.9
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:  Runtime     |       Blocked By:
  performance bug                    |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by dfeuer):

 The same should probably apply to the (non-exported) `between` function in
 `GHC.IO.Encoding.UTF8`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9638#comment:1>
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