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

[GHC]

#13211: NegativeLiterals -0.0 :: Double
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        Reporter:  rwbarton          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:  newcomer
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 Nolan):

 I'm new to ghc and this is my first ticket.

 Patch above dosn't work as expected. I changed rule for negative floating
 point literals so that it triggers(as I believe) only on non zero
 literals. Having that this shouldn't change default(without
 -XNegativeLiterals) behaviour of lexer for such cases.

 But for some reason it doesn't work. Non zero literals look to be correct
 as well as positive zero but negative zero produces such error. I don't
 know what it means and can't find source of this error. Searching though
 whole project for those messages and function it didn't help. What can it
 be?
 {{{
 nolan at NolanPC:~/ghc$ ./inplace/bin/ghc-stage2 -XNegativeLiterals -e "-0.0"
 <interactive>:0:1: error:
     • Non type-variable argument in the constraint: Num (a -> b)
       (Use FlexibleContexts to permit this)
     • When checking the inferred type
         it :: forall b c a. (Num (a -> b), Num (b -> c)) => a -> c
 }}}

 Maybe I get this wrong and this trick will not work. Do you have any ideas
 of how this feature should be implemented?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13211#comment:1>
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