You can build a basic effect system in the same way you do in Haskell (except without typeclasses you need to be more explicit about which monad you're living inside of). Without syntax sugar this is a bit noisier, of course. Also, without typeclasses transformer stacks are difficult and `mtl`-style transformers are impossible (I think).

So, you can think of OCaml's semantics as living inside of a monad. Or just do it all implicitly by giving basic semantics to ;.

And the way I was speaking I mean to say that "mutable state is natural" too. I don't know that it is universally, but it's certainly something that makes 90% of programmers today feel comfortable.