Modifying "sync" to do parallel stuff

concurrent_sync.js

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]);
      }
      else {
        iterable.next(vals); // resume with an array
      }
    }
  }

  resume = function(err, retVal) {
    var slot = ops;
    ops++;

    return function(err, retVal) {
      if (err) { 
        iterable.raise(err);
      }
      else {
        vals[slot] = retVal;
        check();
      }
    };
  };

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