[GHC] #9816: Add function for size-checked conversion of Integral types

[GHC]

#9816: Add function for size-checked conversion of Integral types
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       Reporter:  spl                |                   Owner:
           Type:  feature request    |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  libraries/base     |                 Version:  7.9
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 Based on the discussion in
 [http://thread.gmane.org/gmane.comp.lang.haskell.libraries/23338 this
 thread], I would like to add a function to the {{{base}}} library that is
 similar to {{{fromIntegral}}} but only successful if the argument fits in
 the result type.

 If possible, I would like to get this into 7.10. My apologies for running
 late on it. Hopefully, since it is a relatively small change overall, the
 "only" controversy will be bikeshedding.

 I have concluded that adding @hvr's {{{intCastMaybe}}} from
 [http://hackage.haskell.org/package/int-cast int-cast] is the best
 possible option. Previously, I thought a {{{Bounded}}}-based version was
 also useful; however, I realized that it did not deal properly with
 conversions like {{{Int<->Word}}}/{{{Int8<->Word8}}}/etc. as well as
 {{{intCastMaybe}}} and would need specialized versions that
 {{{intCastMaybe}}} provides automatically.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9816>
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