[GHC] #15183: Expose the SNat type and the natSing method

[GHC]

#15183: Expose the SNat type and the natSing method
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           Reporter:  dfeuer         |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Core           |           Version:  8.2.2
  Libraries                          |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Currently, neither the `SNat` type nor the `natSing` method of `KnownNat`
 are exported from `GHC.TypeLits`. This is weird and awkward. There's no
 apparent reason not to expose the `SNat` ''type'', although it may make
 sense not to expose its definition. It also could possibly make sense not
 to expose the fact that `natSing` is a ''method'' of `KnownNat`, but
 there's no apparent reason not to export a function with its type. Can we
 just do those?

 1. Export the `SNat` type.
 2. Export a function with the type of `natSing`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15183>
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