[GHC] #14111: strange error when using data families with levity polymorphism and unboxed sums and data families

[GHC]

#14111: strange error when using data families with levity polymorphism and unboxed
sums and data families
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        Reporter:  carter            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:  13737             |             Blocking:
 Related Tickets:  #14457            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 Ryan, what happens if you try this example in your patch:

 {{{#!hs
 type S = T
 data T where
   MkT :: Int -> S
 }}}

 That works today. But I have a feeling it will fail with your patch. The
 problem is actually an oversight in Phab:D4974, but I was surprised that
 Phab:D4974 actually accepts the program above. However, a sneaking
 suspicion is that, with your patch as well, the program will be rejected.
 I'm wondering if I should bother fixing this (maybe it wasn't an oversight
 after all), and so I'm curious to know the behavior on your branch with
 that program.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14111#comment:23>
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