Natural language phrase generation in a very complex foreign language that follows recursive syntax trees. And making a GUI to handle and edit these syntax trees visually.
The book takes you through simpler examples, but I found that the exercises did an excellent job of drilling a kind of recursive problem solving skill into your head. You represent the data in types, and then keep breaking the problem down into smaller functions until it is solved. It's almost magic. After being armed with this way of thinking (through lots of practice with the many exercises) I found that problems I didn't know where to begin with just melted away.
>then keep breaking the problem down into smaller functions until it is solved.
That technique definitely works. i have used it. so have tons of others.
it closely resembles the methods of structured programming and stepwise refinement.
Both those terms are probably there in Wikipedia, because they are notable, being well known. and check out niklaus wirth. ditto. turing prize winner or other major awardee. pascal. modula family languages. etc.