The library to easily map/each/reduce/map_reduce/filter deeply nested maps/keywords/lists, called Iteraptor has been released. Besides standard map-reduce operations, it allows flattening nested terms and deflattening them back, and provides a couple of helper methods for low-level traversing them.

There is a blog post describing the interface in details, and Hexdock.

We were using it in production for months, but since we were not able to catch more bugs on our limited set of nested structures, I would be glad to hear about other use-cases where it fails to traverse the nesteds properly.

Also, it’s extremely handy when one needs to filter out some deeply nested keys, or get just the second level of a nested map, or produce a flattened keyword list out of external config file