[GHC] #13186: Change EvNum to EvNum :: Natural -> EvLit

[GHC]

#13186: Change EvNum to EvNum :: Natural -> EvLit
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           Reporter:  phadej         |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #8306 #8412
                                     |  #13181
Differential Rev(s):                 |         Wiki Page:
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 Currently we carry `Nat` kind as an Integer internally.

 Just changing the type of EvNum (and related isomorphic types like
 `HsTyLit` etc) does pretty far. The core problem is that we should be able
 to output Natural literals into Core.

 Also this would need change to parser, to accept only Naturals in types.
 Currently negative literals are caught in the renamer (due the fact that
 template-haskell might inject negative integers as well).

 This will propagate to template-haskell, changing TyLit there as well.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13186>
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