ML has always had easy mutables in the form of references, and the closest deployed language to Standard ML (Ocaml and Reason), has always had for-loops and while-loops. Mutable references are used frequently.

Rust is great because it's low level, high-performance, non-garbage collected and it's primary inspiration for higher-level programming is languages like ML and Haskell.

Thanks! I actually do use Rust as my main professional language (since my company’s product is based on timely-dataflow and differential-dataflow, so it was the only natural choice).

But I’m always curious about how it stacks up against other languages I’m less familiar with that share similar ideas.

IMO both language types offer shared state and immutable data structures so I don't see them as mutually exclusive. As the Rust guys I've heard say "sharing state and mutation are fine, just not together". It's a question of whether the problem your trying to solve is better as a highly mutable one with "sharing" (e.g I'm thinking system programming with contended system resources) or you want to share data across many threads simultaneously and are happy with slower single threaded performance for greater multi threaded throughput (writes are rare so sharing and locking on an atomic ref on occasion is OK so you want structural sharing of data). Rust helps the coder avoid the issues when coding in the traditional "sharing and mutation" paradigm especially without a GC; languages like F# have some modern things to do this like atomic refs for data sharing, flagging mutables, async lock types, support for imperative programming etc. Both approaches work and IMO suit different kinds of problems; good to have both available.