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? 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.Miljenovic@gmail.com IvanMiljenovic.wordpress.com