I think Erlang does? I don't really know Erlang, but AFAIK there's no way to share anything mutable between processes. Any data which is shared is (semantically

I think Erlang does? I don't really know Erlang, but AFAIK there's no way to share anything mutable between processes. Any data which is shared is (semantically) copied when it's sent to a different process. (Ignoring FFI, and such.) Same thing applies to the STM "subset" of Haskell -- conformance to which is statically verified by the type checker[1]. [1] There's no particular magic going on wrt. checking -- STM is a monad. It just happens to have "magic" runtime support.