This. Roughly a year ago I got interested in efficient immutability for my write-from-scratch-in-C Lisp [0] and started to write a HAMT implementation in C [1],

This. Roughly a year ago I got interested in efficient immutability for my write-from-scratch-in-C Lisp [0] and started to write a HAMT implementation in C [1], along with a (somewhat hacky, you have been warned) benchmarking suite [2]. The docs are only 70% done (in particular the "putting it all together" part is missing) but it has been a really interesting and enlightening journey so far and can only recommend embarking on this path to everyone. [0]: https://github.com/mkirchner/stutter https://github.com/mkirchner/stutter [1]: https://github.com/mkirchner/hamt https://github.com/mkirchner/hamt [2]: https://github.com/mkirchner/hamt-bench https://github.com/mkirchner/hamt-bench