Dart2

int sum(List<int> intList, int index) {
  if (index == 0) {
    return intList[index];
  } else {
    return intList[index] + sum(intList, index - 1);
  }
}

void main() {
  var test = [4, 2, 3, 4];
  var result = sum(test, 3);
  print(result);
}