I'm willing to believe that in the end it will all have been worth it. But I didn't find that enough to continue reading this particular series because after a while it didn't seem to be motivated by any useful problems for programmers, as was promised in the title.

Here's my heuristic for whether a problem makes a good example: whether or not it's the best tool for the job, would you write a program to solve it in C or Java or Go? If not, I'm skeptical it's solving a problem that exists outside the functional programming universe.

There are plenty of techniques that solve problems that only make sense within the particular ecosystem where you find them; lots of Java tools are like that, for example.