Apologies for not understanding. And I admit, it's hard to communicate in the abstract, so I might still not understand the question.
replyIf it helps: AFAICT, Valen's borrow checker preserves the same ecosystem-wide concurrency benefits that Rust has. For precedent, check out GhostCell [0] which is not only _compatible_ with Rust's concurrency but gives it some interesting new abilities. Valen's approach could be thought of as a more ergonomic form of GhostCell that better tracks the relationships between multiple groups (brands).
I could give a better answer if we had an example to toss around where we think Valen might force things to be single-threaded.
Rust 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.
replyI 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.
replyHow widespread are locks in typical Rust code?
replyVery rare compared to C code.
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