[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 request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #8306 #8412       |  Differential Rev(s):
  #13181                             |
       Wiki Page:                    |
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Comment (by phadej):

 Currently we can get:

 {{{
 Prelude> :set -XDataKinds -XNegativeLiterals
 Prelude> :m +Data.Proxy
 Prelude Data.Proxy> Proxy :: Proxy (-1)
 }}}

 Even this case could (and should?) be ruled out in parser, thru `template-
 haskell` you can still inject negative integers. Thus the workaround fix
 is currently in the renamer.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13186#comment:3>
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