>Of course, just the fact that abstracting over those things is possible doesn’t mean it is useful. In a pure FP language it might be necessary, but why should I bother with weird mathy things in my imperative language that has side effects and global state? You really have to start by explaining why composability is such a nice thing to have, and that gives the motivation for various FP patterns that are, fundamentally, all about composability.

But then you start running into the nasty issue that when you need to compose multiple monads, you find out that monad transformers don't always commute!