[GHC] #8767: Add rules involving `coerce` to the libraries

[GHC]

#8767: Add rules involving `coerce` to the libraries
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        Reporter:  nomeata                       |            Owner:
            Type:  task                          |           Status:  new
        Priority:  normal                        |        Milestone:  7.8.1
       Component:  libraries/base                |          Version:
      Resolution:                                |  7.8.1-rc2
Operating System:  Unknown/Multiple              |         Keywords:
 Type of failure:  None/Unknown                  |     Architecture:
       Test Case:                                |  Unknown/Multiple
  tests/simplCore/should_run/T2110.hs            |       Difficulty:
        Blocking:                                |  Unknown
                                                 |       Blocked By:  8718
                                                 |  Related Tickets:  #2110
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Changes (by thoughtpolice):

 * cc: ekmett (added)
 * status:  closed => new
 * resolution:  fixed =>


Comment:

 (Whoops, accidentally closed.)

 Richard, Edward probably has something to say about the `fmap` rule, but
 in general do we want it right now when it can break things? I'm under the
 impression there's not a sensible and safe one we can write that won't
 break for non-lawful Functors. (I guess we can tell everyone to always
 write ones that obey the rules, but I'm not sure how much that might
 backfire).

 There was some discussion of related approaches a few months ago around
 ICFP time (don't have a link on me). Anyway, worth a good discussion.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8767#comment:8>
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