Mon Dec 9 20:53:23 EST 2019

composite keys vs. nested maps

These are isomorphic, so the only difference between these structures
is implementation.  But I find that switching to flat map with
composite key representation opens doors.  It makes code simpler.  It
allows for restructuring, as the structure itself (the grouping of
keys) can be made compositional, i.e. functions can create collections
of keys to isolate substructure that might be different from the
(arbitrary) nested structure.

This seems to work well when the idea of "coordinate" is more
appropriate than "path", i.e. individual dimensions are indepenent,
not one conditional on the other.