At least in JavaScript, you could mark all of your functions as `async`.

This would mean that function would have to return a Promise and go back to the event loop which would add overhead. I imagine it'd kill performance since you'd essentially be context switching on every function call.

The obvious workaround for this is to say "I want some of my code to run serially without promises", which is essentially is asking for a `sync` keyword (or, `async` which would be the inverse).