[GHC] #13211: NegativeLiterals -0.0 :: Double

[GHC]

#13211: NegativeLiterals -0.0 :: Double
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           Reporter:  rwbarton       |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:  newcomer       |  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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 Compare
 {{{
 rwbarton at morphism:~$ ghc-8.0.1 -e '-0.0'
 -0.0
 rwbarton at morphism:~$ ghc-8.0.1 -XNegativeLiterals -e '-0.0'
 0.0
 }}}
 This behavior is logical, but unexpected. The logic is that with
 `NegativeLiterals` the literal `-0.0` means `fromRational ((-0)%0)`, which
 equals `fromRational 0`, which for `Double` is positive zero, not negative
 zero.

 But this seems unfortunate. Perhaps it would be best if `-0.0` (or `-`
 applied to any other literal mathematically equal to zero) was desugared
 as `negate 0.0` even under `NegativeLiterals`, since there doesn't seem to
 be any other reason to write `-0.0`.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13211>
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