Fringe tree is an intentionally poor persistent functional binary tree implementation that grew out of wanting an example to work on the 'same fringe' problem.
The same fringe problem is answering the question of if two trees represent the same sequence of data. It's traditionally a good example of the power of co-routines.
Using good, self-balancing, tree structures makes many of the problems with finding the sequence of data trivial, and collapses many different tree constructions into the same exact result, not just an equivalent one.
The repository is also my work on, if not 'best', at least good practices with CMake and emerging consensus on file and directory layout.