https://blog.redelastic.com/a-guide-to-scala-collections-exploring-monads-in-scala-collections-ef810ef3aec3

This document is intended to provide an educational guide for beginning developers working in Scala, to enhance their understanding of both Scala collections and monads in order to improve code quality and developer fluency. We hope that this guide is both educational and inspirational. Mastering monads along with Scala collections will lead to much more robust, idiomatic and functional Scala, and is a heck of a lot more fun than reinventing the wheel when these two abstractions are perfect for the problems that they help to solve.

In order to get the most out of this series, readers should have a basic understanding of functional collections in Scala (or a Java-based library like VAVR), specifically operations such as map, reduce, and flatten.