[GHC] #4959: Warning about variables with leading underscore that are used anyway

[GHC]

#4959: Warning about variables with leading underscore that are used anyway
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        Reporter:  Lemming           |            Owner:
            Type:  feature request   |           Status:  new
        Priority:  low               |        Milestone:  7.10.1
       Component:  Compiler          |          Version:  7.0.1
  (Parser)                           |         Keywords:  warning unused
      Resolution:                    |  underscore variable
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by Lemming):

 Replying to [comment:6 goldfire]:
 > I don't have too strong an opinion here, but I want to note that
 sometimes the use of a variable with a leading underscore is intentional.
 In particular, I have found this necessary when I use CPP to optionally
 disable a certain chunk. I don't want warnings to appear when I disable
 the chunk (eliminating the one use of a variable, to which I prepend a
 `_`) or when I enable the chunk (now using a variable with a leading
 underscore).

 Could you move the conditionally used variable into the `#ifdef` block?

 > So, I have a slight preference for "no change" here, but it really is a
 slight preference -- I do see and understand the original poster's point.

 It should be possible to disable the used-underscore-warning. If the CPP
 problem arises often and is hard to workaround, then it would be still
 great to enable the used-underscore-warning on demand.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4959#comment:7>
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