> > > We can’t perform arithmetic on an Option<int> any more than we could on a List<int>.

Is actually kind of a weird point to make. There are number of ways to add together List<int> including:

    listA.zip(listB).map(([a, b]) => a + b);

Similarly adding together two optionals could be done with:

    optionalA.zip(optionalB).map(([a, b]) => a + b);

Or if you would rather:

    optionalA
      .zip(optionalB)
      .map(([a, b]) => a + b)
      .or(optionalA)
      .or(optionalB)