The thing is the abstractions on the last code are optimized for solving a far more general version of the problem, that just to exercise (not even exhaust) all the kinds of variation supported would take hundreds, probably thousands, of lines with code taking the initial approach. But you don't really have even a hint of that, because the article doesn't show at each abstraction level a broader problem, the cost of solving it without the new abstractions introduced, and then the benefit of the abstractions.