On Fri, Apr 9, 2010 at 6:44 AM, Ivan Lazar Miljenovic < ivan.miljeno...@gmail.com> wrote:
> > As of 6.12.1, the new -fwarn-unused-do-bind warning is activated with > -Wall. This is based off a bug report by Neil Mitchell: > http://hackage.haskell.org/trac/ghc/ticket/3263 . > > However, does it make sense for this to be turned on with -Wall? Personally, I find it to be tremendously noisy and unhelpful, and I always edit my .cabal files to turn it off. I think of it as a usability regression. > For > starters, why should this warning apply only to do blocks and not to > explicit usage of >>, etc.? That is, the following code (as specified > in the above bug report) generates an error: > > do doesFileExist "foo" > return 1 > > yet this doesn't: > > doesFileExist "foo" >> return 1 > > If monadic code is going to return an error, then shouldn't _all_ > monadic code do so, and not just those in do blocks? > > Secondly, a fair number of packages seem to be disabling this globally; > the packages I know of (from mentions on mailing lists and grepping on > /srv/code/*/*.cabal on code.haskell.org) that have the > -fno-warn-unused-do-bind option being passed to GHC in their .cabal file > include: > > * HsOpenCL > * leksah-server > * xmonad (including xmonad-contrib) > * xmobar > * pandoc > > My reason for bringing this up is that I'm soon about to release a new > version of my graphviz library, and am debating what to do. Note that > most of these errors are being caused by usage of a monadic-style of > parsing (before anyone tells me I should be using an Applicative style > instead, polyparse doesn't support Applicative, so I can't) and as such > the "return value" is being evaluated anyway. The way I see it, I have > 4 options: > > 1. Do as the error suggests and preface usage of these parser > combinators with "_ <-". > > 2. Use some function of type "(Monad m) => m a -> m ()" instead of doing > "_ <-". > > 3. Duplicate the parser combinators in question so that I have one > version that returns a value and another that does the main parser > and then returns (); then use this second combinator in do blocks > where I don't care about the returned value. > > 4. Put "-fno-warn-unused-do-bind" in the .cabal file. > > The first two options don't appeal to me as being excessive usage of > boilerplate; the third involves too much code duplication. However, I > am loath to just go and disable a warning globally. > > What does the Haskell community think? Is -fwarn-unused-do-bind a > worthwhile warning (and code should be updated so as not to cause it to > find anything to warn about)? Or is it more of a hindrance to be > disabled? > > -- > Ivan Lazar Miljenovic > ivan.miljeno...@gmail.com > IvanMiljenovic.wordpress.com > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >
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