We talk a little bit about Rust and functional programming in the book: https://doc.rust-lang.org/book/second-edition/ch13-00-functi...

> Rust’s design has taken inspiration from a lot of existing languages and techniques, and one significant influence is functional programming. Programming in a functional style often includes using functions as values, by passing them in arguments, returning them from other functions, assigning them to variables for later execution, and so forth. We won’t debate here the issue of what, exactly, functional programming is or is not, but will instead show off some features of Rust that are similar to features in many languages often referred to as functional.