Mon Sep 4 23:32:55 EDT 2017

More general imperative "derivatives"

I'm still wondering how far this idea can be pushed.  Especially the
part where starting from an empty model becomes an option.

Currently, how the diffing works, this requires the creation of an
entire tree, which is not likely what is desirable.  It's probably
better to map to creation of empty nodes, and then fill them with