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function sync(gen) {
  var iterable, resume;

  resume = function(err, retVal) {
    if (err) iterable.raise(err); // raise!
    iterable.next(retVal);
  };

  iterable = gen(resume);
  iterable.next();

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sync(function* (resume) {
  var oneAndTwo = yield [_get("test1.txt", resume()), _get("test2.txt", resume())]
  var three     = yield _get("test3.txt", resume())
  
  log(oneAndTwo[0] + " - " + oneAndTwo[1] + " " + three)
});

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// async

async.waterfall([
  function(callback) {
    async.parallel([
      function(callback) {
        _get("/token", callback);
      },
      function(callback) {
        _post("/key", callback);

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app.get('/home', prioritize(prioritizer, responder));

var queues = [];

function flush() {
  if (!flush.polling) {
    flush.polling = setInterval(function() {
      var x;
      for (var i = 0; i < queues.length; i++) {
        for (var j = 0; j < queues[i].length; j++) {

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Some notes about the gist:

• Calling "sync" creates an array to keep track of return values from any asynchronous operation.

• The "resume" method is called in your generator code and its return value is passed as the callback to your asynchronous operation. Calling "resume" causes a counter to increment, letting your "sync" method know how many asynchronous operations are in flight.

• The return value of "resume" is a function that causes the result of the asynchronous operation to be placed into the data structure in #1. Immediately after doing this assignment, we check to see if there are any outstanding asynchronous operations. If not, we resume the generator with either an (ordered) array containing the results of our asynchronous operations or (in the event of only one operation having been fired off)

The important thing to note is that both asynchronous operations have been fired off before yielding. Each callback (passed to these asynchronous calls) is the return value from the call to "resume" -

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function sync(gen) {
  var iterable, resume, check, vals, ops;

  vals = [];
  ops  = 0;

  check = function() {
    if (vals.length == ops) {
      if (ops == 1) { 
        iterable.next(vals[0]);

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a = [["a", 1], ["b", 2]]
h = a.inject Hash.new(9999) do |hash, pair|
  hash.merge Hash[[pair]]
end

h["a"]   # 1
h["foo"] # 9999

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class StatefulCalculator
  def initialize
    @total = 0
  end

  def add(x)
    @total += x
    self
  end

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class StatefulCalculator
  def initialize
    @total = 0
  end

  def add(x)
    @total += x
    self
  end
  

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class StatefulCalculator
  def initialize
    @total = 0
  end
 
  def add(x)
    @total += x
    self
  end