> IO is a library concern in Rust, not a language concern. It often is a language concern: no async/await in the compiler or language-assisted yielding/schedul

> IO is a library concern in Rust, not a language concern. It often is a language concern: no async/await in the compiler or language-assisted yielding/scheduling means difficult or impossible concurrency model. With Rust's borrow checker, IO (already unsafe C FFI) + callbacks are hard to write in a pleasing and safe way.