//   This is an abstract list
const arrayList: List<number> = [1, 2, 3];

//  This is also an abstract list
const aList: List<number> = {
  at(index) {
    return index;
  },
  length: Number.MAX_SAFE_INTEGER,
};

//  This is a giant list for which elem.at(x) === x^2
const squareList: List<number> = {
  at(index) {
    return index * index;
  },
  length: Number.MAX_SAFE_INTEGER,
};