Functional Programming's Toolkit: Monads, Monoids and Functors

HN recommends it as the best beginner-friendly introduction to monoids, monads and other FP vocabulary.

Scott Wlaschin demystifies functional programming terms like monads, monoids, functors and catamorphisms by showing how they fit into a small toolkit. He applies them to problems such as missing data, list handling, and functional dependency injection.