You can basically get the type of structured programming author is looking for with fully public structs in a functional language. And the pureness of functional paradigm is a bit of a strawman. Coming off of mostly C, C++, ruby, and python, I exclusively program in functional languages and have been for almost a decade now (wow!), and none of the fp langs (julia, elixir, erlang, react) that I have used have been "purely" functional. They all expose state (using different techniques - (bang functions, actors, actors, hooks) which are extremely well calibrated to the needs of their practioners. While that leads to a bit of fragmentation, it does also mean that the quality of code you release is better, because you're protected from making common mistakes that in my pre-FP experience, led to much teeth gnashing and hair pulling.