alt Hacker NewsRust needs shared xor mutable in order to prevent data races on non-atomically accessed data. You said that Valen can _express_ shared xor mutable, but perhaps you haven't clarified whether this also interacts with equivalents to Rust's Send and Sync to enable the same fearless concurrency.
I mean the article doesn't talk about this aspect of the language, but Send and Sync are orthogonal to borrow checking. I don't see why you couldn't use Rust's exact design in Valen.