Library proposal: add a Location interface for element-wise operations on Data.Map (#4887)

[Ross Paterson]

On Wed, Jan 12, 2011 at 10:53:02PM +0100, Johan Tibell wrote:
> I tried to improve the performance today without much success (but
> much staring at Core). I wonder if the extra allocation of Path data
> constructors is hurting performance.
> 
> Is it worth adding this Interface for all its coolness? Simply using
> 'lookup' plus 'insert' is simpler, as powerful, and only 7% slower.

I've also had no success in speeding it up.  It's disappointing that
having the extra information (whether the key was there or not) doesn't
help, but I think I agree.