[GHC] #10774: Use `Natural` rather than `Integer` in `GHC.TypeLits`

[GHC]

#10774: Use `Natural` rather than `Integer` in `GHC.TypeLits`
-------------------------------------+-------------------------------------
              Reporter:  hvr         |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:  7.12.1
             Component:              |           Version:  7.10.2
  libraries/base                     |
              Keywords:  TypeLits    |  Operating System:  Unknown/Multiple
  Natural                            |
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
-------------------------------------+-------------------------------------
 When the numeric type-literals were implement via `GHC.TypeLits` there was
 no `Natural` type in `base` yet. But since GHC 7.10 we finally have
 `Natural` available in base!

 Specifically, the following 3 type-signatures in `GHC.TypeLits` cpmtaom
 `Integer` that ought rather be `Natural`s:

 {{{#!hs
 someNatVal :: Integer -> Maybe SomeNat

 natVal :: forall n proxy. KnownNat n => proxy n -> Integer

 natVal' :: forall n. KnownNat n => Proxy# n -> Integer
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10774>
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