[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 request   |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Core Libraries    |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 OK. Is your intention to provide an alternative to the current
 `Proxy`-based API? (For instance, `natVal :: KnownNat n = Proxy n ->
 Natural`, and you're suggesting to augment it with something like
 `fromNatSing :: SNat n -> Natural`?) If so, it may also be worth
 considering adding `SNat`-consuming counterparts to `sameNat` and
 `someNatVal` (the latter of which would require something like `data
 SomeNatSing`, which is like `SomeNat`, but having an `SNat` as a field
 instead of `Proxy`).

 Also, `KnownSymbol`/`symbolSing` has similar design considerations.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15183#comment:3>
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