[GHC] #10178: hs-boot/hsig ambiguity empty data declaration or type with no constructors

[GHC]

#10178: hs-boot/hsig ambiguity empty data declaration or type with no constructors
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        Reporter:  ezyang            |                   Owner:  ezyang
            Type:  bug               |                  Status:  new
        Priority:  lowest            |               Milestone:
       Component:  Compiler          |                 Version:  7.11
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by ezyang):

 Similarly, when I write:

 {{{
 class C a
 }}}

 it is ambiguous whether or not it is a fully-specified empty type class,
 or an abstract type class. In fact, for this one we don't even distinguish
 the two cases in an hi file.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10178#comment:1>
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