Comment by bob1029

> Make every function async, and provide extra parameter indicating to not actually unwind the stack and execute synchronously instead. Comes with performance penalty.

I think ValueTask<T> in C#/.NET can approach this use case - It avoids overhead if the method actually completes synchronously. Otherwise, you can get at the Task<T> if needed. From a code perspective, you await it like you normally would and the compiler/runtime figures out what to do.