It provides as-pure-as-useful functional data structures to improve the functional programming experience with Rust. It implements a set of instances of the foundational functional type classes (e.g. Functor, Monad) for a large number of data structures.
The implementation tries to be as close to the pure functional implementations of these data structures, but also tries to remain practical given the specifics of the Rust programming language.
This is currently a means for myself to explore functional programming in general and also to understand what is possible within the inherent limits of Rust. If the overall approach turns out to be possible without negating Rust's design principles and performance goals the plan is definitely to move this to production grade functional library.