Proposal: add ifM and whenM to Control.Monad

[Herbert Valerio Riedel]

On 2014-04-21 at 09:49:40 +0200, Herbert Valerio Riedel wrote:
> On 2014-04-21 at 00:35:03 +0200, Edward Kmett wrote:
>> mif appears to pass the naming convention rules. It looks strange, but we
>> can chalk that up to lack of exposure.
>
> I'm +1 on using `mif`/`mwhen`/`munless` (assuming all those pass the
> current naming convention), because otherwise adding an exception to the
> naming convention for Control.Monad entities would also require
> rewording the existing naming convention in the Haskell Report.
>
> Moreover, since 'Control.Monad' is often imported unqualified, we'd
> probably cause clashes in existing packages (and together with non-PVP
> upper-bounds on base that'd mean build failures)
>
> A quick heuristic grep over all Hackage packages results in quite a bit
> of packages containing the ifM/whenM/unlessM:

All that said, I'm (also) +1 the ifM/whenM/unlessM variants, under the
condition that

 - somebody comes up with an amended wording for Haskell Report 2010's
   "13.2.1 Naming conventions"[3] section that avoids the inconsistency, and

 - somebody takes care to inform/pester/annoy the maintainers of the 70+
   package that to make sure that those packages aren't left broken (if
   they break) for long after this gets merged into GHC HEAD [1][2]


 [1]: The motivation for this being, that I'd like people to be able to use
      nightlies of GHC HEAD, e.g. via Travis-CI to test their packages'
      'master' branch early for potential GHC HEAD breakages (and report
      those to GHC HQ if it looks like a GHC bug), this however is
      thwarted if the builds start failing due to build-deps being
      broken.

 [2]: Ironically, the easiest way to fix packages (w/o breaking compat for
      base<4.7.1) would be to simply make sure the new
      ifM/whenM functions are not imported, and that the package-local
      hand-rolled versions of ifM/whenM are continued to be used...

 [3]: http://www.haskell.org/onlinereport/haskell2010/haskellch13.html#x21-19500013.2