I watched this video because I was interested in Rust, but the side-by-side comparisons of code snippets versus Haskell just sold me on Haskell. If something needs speed optimization, then isolate that piece of code and optimize it only, keeping all of the rest of the code so much more readable and maintainable, rather than switching entirely to a low-level language and dealing with all that extra unreadable crap throughout the entire codebase.
any; that is my point; functional programming is a paradigm, not a particular set of languages; a feature should not be considered to be a functional programming feature just because it tends to be provided by some functional languages [haskell, ml]