Proposal: Add `restriction` to Data.Map and Data.IntMap

[Ross Paterson]

On Thu, Jul 14, 2016 at 12:02:51PM -0400, David Feuer wrote:
> On Jul 14, 2016 11:55 AM, "Ross Paterson" <R.Paterson at city.ac.uk> wrote:
>     One might also want the counterpart of Data.Map.difference for similar
>     reasons.
> 
> If you name it, it will come!

Whatever they're called, putting the set argument second for both functions
would match Data.Map.interection and Data.Map.difference, which would help.