Control.Monad proposal: Add whenJust

[Simon Hengel]

On Sat, May 18, 2013 at 03:08:33PM +0100, Ian Lynagh wrote:
> On Wed, May 15, 2013 at 10:40:45PM +0200, Bas van Dijk wrote:
> > On 15 May 2013 18:14, Edward Kmett <ekmett at gmail.com> wrote:
> > > Personally, I'd be all for just moving Foldable (and Traversable) into the
> > > Prelude and retiring the monomorphic versions of the functions they supply.
> 
> I'd prefer to remove the monomorphic functions, but not to add anything
> to Prelude.

The issue here is that his would make it very hard to write backward
compatible code.  We already have seen this by removing Prelude.catch.
GHC HQ mitigated this by making a "hidden import" a warning.  But if you
want -Wall-sane code you still need to always import Control.Exception
qualified.

Personally I'm strongly against removing the monomorphic versions
without providing suitable alternatives.

Cheers,
Simon