Untitled

// produce: accepts a cb which is called with an array of items
// initial: initial array of results to return
// returns a function which accepts a cb which is called with one item
// each time it is called
function generator(produce, initial) {
  var items;
  var waiting = [];

  var next = function (cb) {
    if (items && items.length) {
      cb(items.shift());
      if (items.length == 0) consume()
    } else {
      waiting.push(cb);
    }
  }

  function consume () {
    produce(function (new_items) {
      items = new_items;
      while (waiting.length && items && items.length) {
        next(waiting.pop())
      }
    });
  }

  if (initial && initial.length) {
    items = initial;
  } else {
    consume();
  }

  return next;
}

// example
var sys = require('sys');
var print = (function (s) {sys.print(s+"\n")})

var my_producer = (function () {
  var i = 0;
  return function (cb) {
    setTimeout(function () {
      cb([++i, ++i]);
    }, 1000);
  }
})();

var my_generator = generator(my_producer);

my_generator(print);
my_generator(print);
my_generator(print);