code: function(task) {
          var tasks = arguments, n = tasks.length;
          return function() {
            var args = slice.call(arguments), callback = args.pop(), results = [];
            for (var i = 0; i < n; i += 1) {
              (function(task, args, i) {
                function taskCallback(error, result) {
                  if (!callback) { return; }
  
                  results[i] = arguments.length < 3 ?
                    result : slice.call(arguments, 1);
  
                  if (error || all(results, n)) {
                    callback.apply(null, [error].concat(results));
                    callback = null;
                  }
                }
  
                task.apply(null, args ? args.concat(taskCallback) : [taskCallback]);
              }(tasks[i], args.shift(), i));
            }
          }
        }
docs: Combines multiple continuation-style functions ("tasks") into a
  single function.
  
  All tasks are invoked immediately. The callback will be invoked with
  the first yielded error (if any) and all results available at
  that time.
  
  @param {...function(...?=, function(Error, ...?=))} task Any number of
  continuation-style functions / "tasks".
  @returns {function(...Array, function(Error, ...?=))} A function taking
  arrays of arguments to be passed to the tasks and a callback to
  execute when all tasks have finished or an error has been yielded.