[GHC] #2110: Rules to eliminate casted id's

[GHC]

#2110: Rules to eliminate casted id's
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        Reporter:  igloo             |            Owner:
            Type:  feature request   |           Status:  patch
        Priority:  lowest            |        Milestone:  7.6.2
       Component:  Compiler          |          Version:  6.8.2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Changes (by nomeata):

 * status:  new => patch


Comment:

 With `master` open for new stuff, I’d like to get this there, preferably
 within the next one or two weeks, to reduce the number of my patches that
 are floating around, so I’m marking this as please review.

 Open tasks are
  * Fixing the matching against `unsafeCoerce` (needs thought)
  * Actually adding rules to the libraries.
  * Documenting this somewhere

 I’ll open separate tickets for these once this one is in.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/2110#comment:42>
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