Hello,

I believe it would be more appropriate for delay() to throw a custom exception specific to cancellation (e.g., CanceledException) instead of a standard PHP's \RuntimeException.
This would allow developers to more easily distinguish between expected cancellations and other unexpected errors.

Additionally, it would be great if ReactPHP could provide a helper function, like this one:

function throwIfCanceled() {
 await(new Promise(
 function($resolve) {
 $resolve(null);
 },
 function() {
 throw new CanceledException();
 }
 ));
}

This would allow developers to handle the cancellation of asynchronous tasks at specific points in the code, such as after each iteration of a long-running loop (essentially the same as delay(0)).