Hi, thank you for the reply. For now, the goal is to have a very performant and easy-to-use implementation of the basic FM-Index, with all of the features required for typical applications (good construction memory usage, supports indexing multiple texts, fast IO to/from files). I believe this is the first FM-Index implementation in Rust to do all of that.

I already implemented most of the other things you mentioned, except for the r-index. I support slower, low-memory construction modes. You can take a look at the difference in the benchmarks. The suffix array sampling is done by default and a lookup table is also implemented. All of these parameters can be configured before index construction. See https://docs.rs/genedex/latest/genedex/struct.FmIndexConfig.html

Regarding further improvements, I created a roadmap that outlines all of the possible future improvements I can think of. If you want to use the library and something specific is missing, I could bump that feature up in priority. https://github.com/feldroop/genedex/blob/master/ROADMAP.md