Monads. We all know and love them, right? Er, maybe...
Chapters 20 and 21 describe monads from a programmer's point of view. We should read these chapters for review, but I expect there won't be much new material in them for most of us. Chapter 22 looks at monads in terms of category theory, so that's what we'll concentrate on.
Let's read the chapter and do the exercises, then get together for our usual lively and occasionally on-topic discussion. We'll try to get properly underway around 6:15.