Nested CPR patch review

[Matthew Pickering]

Hi all,

I recently resurrected akio's nested cpr branch and put it on
phabricator for review.

https://phabricator.haskell.org/D4244

Sebastian has kindly been going over it and ironed out a few kinks in
the last few days. He says now that he believes the patch is correct.

Is there anything else which needs to be done before merging this patch?

Simon, would you perhaps be able to give the patch a look over?

Cheers,

Matt