docs: function concat(array, separator) {
      // TODO: Create subclass ConcatStream < Stream. Defer
      // subscribing to streams until the value() is called.
      var hasStream = scanArray(array);
      if (hasStream) {
        var stream = new ConcatStream(array, separator);
  
        for (var i = 0, l = array.length; i < l; i++) {
          addDependency(stream, array[i]);
        }
  
        return stream;
      } else {
        return array.join(separator);
      }
    }