Dmitry Kandalov ( / dkandalov ) and I follow along with the example from Chapter 22 of Java to Kotlin, A Refactoring Guidebook (https://java-to-kotlin.dev/). There we write a CSV parser from scratch in Kotlin, and then compare it to the well-regarded Java Commons CSV (https://commons.apache.org/proper/com...)
The chapter is called Classes to Functions, and looks at how functions can represent many of the concepts that in Java would be classes.
This content is also hosted on Dmitry's excellent channel, and is published here with his kind permission.