[Yhc] Data.Map

[Neil Mitchell]

Hi Lane,

Fantastic!

How close to the base libraries are these? Ideally we would have the
patches go to the base library, and flip to using the base library
repo instead. So, as it stands there are several choices:

1) Keep accumulating patches into the Yhc project repo, then at some
point in the future, try and merge the patches back into the base
libs.

2) Move to the base libraries almost now, and try and send the patches
to the base libraries.

3) Do 1,  but keep trying to get the patches into the base libraries
so the diff between our libs and their's remains nothing.

Personally I favour 3 - it seems like least work, but whichever one
you want, its your choice.

I have committed this patch, and done a small sample with Data.Map,
and am very impressed! I ran into one dependancy ordering issue -
these vary with machine - and had to fix that.

Well done!

Neil