Classifying it as "purely functional" (just looking at the slide) is a big mistake though. I would say that Rust "feels functional", but it definitely ain't pure. I can see why that would rile some folks up.
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Definitely agree with you there - it is frustrating for me. If anything, it seems like Rust is doing a great job at bringing more people to FP. Many people have told me that they found Haskell and OCaml much easier after learning Rust. I certainly have.