Proposal: Add concatMapM function (#2042)

[Don Stewart]

bulat.ziganshin:
> Hello Twan,
> 
> Monday, January 14, 2008, 7:41:08 PM, you wrote:
> 
> > I have noticed that many projects include a 'concatMapM' function:
> 
> >    concatMapM :: (Monad m) => (a -> m [b]) -> [a] -> m [b]
> 
> > I think this is useful in general, so let's add it to Control.Monad.
> 
> the one thing that you miss - each time you add popular function to
> the base library, all programs that include this function
> becomes incompatible with next GHC version. i wonder whether anyone
> here has the experience of writing large programs and maintaining them
> through the years?

There has to be some path to migrate code into base.
Do you have any examples of applications that will break, if this is added?

-- Don