As a long-time F# user and current Rust learner, I would say the similarities are mostly cosmetic. First and foremost, F# is functional-first, while Rust isn't

As a long-time F# user and current Rust learner, I would say the similarities are mostly cosmetic. First and foremost, F# is functional-first, while Rust isn't really functional. Rust takes some useful features from functional languages, to be sure, but the overall paradigm is more procedural. A lot of key functional idioms and design patterns don't really fly in Rust because it's difficult-to-impossible to make them play nice with its memory management model. Rust has traits, but not OOP. F# has OOP but not traits or typeclasses. F# is immutable by default, and discourages mutability. Rust is immutable by default, but embraces (and tames) mutability.