[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
              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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 When I write in a boot or signature file:

 {{{
 data Foo
 }}}

 it is ambiguous whether or not this is a fully-specified empty data
 declaration, or a data type which has its constructors unspecified. This
 doesn't matter too much for hs-boot (since you can't use the data
 constructors in any case) but for signatures we might want to force a data
 type to be empty. Though I think this case should be rare.

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