I sometimes wonder whether this is really an optimization problem pretending to be a coloring problem. In some sense, the sync versions of blocking things are

I sometimes wonder whether this is really an optimization problem pretending to be a coloring problem. In some sense, the sync versions of blocking things are generally better in only one way: they can be more performant (run faster, use less memory, generate shorter code, etc). [0]. If a function can be implemented in async/await style, then ISTM the compiler could treat the sync variant as an automatically generated optimization instead of as a totally different (and differently colored) variant. Of course, in languages like Rust with multiple colors of async code (single-threaded or multithreading-capable), this would get very messy. [0] As a major caveat, synchronous code also enforces various state transitions much more efficiently. Want to prove that IO is done (in the sense that the user code is done with it) before closing a file? This is pretty easy in single threaded blocking code.