This issue was originally filed by @seaneagan

In the same way that programming with Futures could benefit from language support (issue #104), programming with Streams could as well. Streams are essentially async Iterables, so an async version of the "for" statement could work for Streams. It probably makes sense to call it "on" which is already a contextual keyword elsewhere. As an example the implementation of the Iterable-based methods on Stream could look identical to how they are in Iterable except replacing "on" with "for":

async bool any(bool f(E e)) {
  on(var e in this) {
    if(f(e)) return true;
  }
  return false;
}

notes:

* the "on" statement would trigger a "subscribe" to the Stream passing onData, onDone, and onError resulting in a StreamSubscription

• as with await, the enclosing function would implicitly return a Future
• as with await, errors within the construct would throw the unwrapped error, not the AsyncError wrapper
• any "break" or "return" in the "on" statement would trigger an "unsubscribe" on the StreamSubscription
• nested "await"s and "on"s could be delimited by "pause()" and "resume()" on the StreamSubscription, and since that's only a best effort, any events which occur before the nested items complete could be buffered for use in later iterations of the "on" statement.

Initial mailing list discussion:

http://goo.gl/8PqcP