[GHC] #11594: closed empty type families fully applied get reduced lazily when in a constraint tuple and fully applied

[GHC]

#11594: closed empty type families  fully applied get reduced lazily when in a
constraint tuple and fully applied
-------------------------------------+-------------------------------------
        Reporter:  carter            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  7.10.2
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9636             |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by adamgundry):

 * cc: adamgundry (added)
 * related:   => #9636


Comment:

 Replying to [comment:3 goldfire]:
 > To paraphrase, you want GHC to recognize that an empty closed type
 family is insoluble.

 Note that empty closed type families are not necessarily insoluble in the
 presence of type-checker plugins. Indeed, the whole point of adding empty
 CTFs was to allow them to be given special reduction behaviour by plugins.
 So I think the implementation should be left alone (but for some
 contrasting views see the discussion on #9636).

 Documentation improvements are welcome, of course. :-)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11594#comment:5>
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