As a Haskell programmer who's done a little bit of Rust, I agree. In Haskell, we do have an escape hatch in the form of the ST monad, which allows you to write

As a Haskell programmer who's done a little bit of Rust, I agree. In Haskell, we do have an escape hatch in the form of the ST monad, which allows you to write an imperative algorithm with mutable state and call it directly from pure code. This is safe (i.e. it doesn't break referential transparency) because there isn't any way to introduce nondeterminism. ST is more restrictive than the IO monad. You can't do file I/O or use concurrency. (You can use the same parallel evaluation tools that are available in pure code.) So, pure Haskell code plus ST is definitely still more restrictive than Rust safe code, but the difference isn't quite as large as it might appear at first. And sometimes Haskell's added restrictions are a good thing, if that's what you want. It is pretty interesting that if you start with the premise that sharing + mutability is bad, you can go either in the direction of Haskell and disable mutability (and then re-enable it in some contexts that are known to be safe) or the direction of Rust and allow sharing and mutability, just not at the same time. Both seem to be good strategies that will appeal to somewhat different audiences.