[GHC] #12665: Make Read instances for Integral types faster, and make them fail fast

[GHC]

#12665: Make Read instances for Integral types faster, and make them fail fast
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        Reporter:  dfeuer            |                Owner:  dfeuer
            Type:  feature request   |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Core Libraries    |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by int-e):

 It's bad enough for integral types:

 {{{
 > reads "\t\n\v\f\r
 \160\5760\6158\8192\8193\8194\8195\8196\8197\8198\8199\8200\8201\8202\8239\8287\12288
 ( ( - 1 ) )  " :: [(Integer,String)]
 [(-1,"  ")]
 }}}

 (Interestingly, `read "-(1)"` fails)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12665#comment:18>
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