[GHC] #13508: Clarify Some Restrictions on Compact Regions

[GHC]

#13508: Clarify Some Restrictions on Compact Regions
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        Reporter:  andrewthad        |                Owner:  ezyang
            Type:  bug               |               Status:  patch
        Priority:  lowest            |            Milestone:  8.2.1
       Component:                    |              Version:  8.1
  libraries/compact                  |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3407
       Wiki Page:                    |
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Comment (by ezyang):

 We should seriously think about how to set up a "can be compacted" type
 class, either by hand in the 'compact' package, or with special solver
 support.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13508#comment:2>
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