Introduction
A co-worker asked about code organization in Functional Programming. He's working with a bunch of Java developers in Node for a single AWS Lambda, and they're using the same style of classes, various design patterns, and other Object Oriented Programming ways of organizing code. He wondered if they used Functional Programming via just pure functions, how would they organize it?
The OOP Way
If there is one thing I've learned about code organization, it's that everyone does it differently. The only accepted practice that seems to have any corroboration across languages is having a public interface for testing reasons. A public interface is anything that abstracts a lot of code that deals with internal details. It could be a public method for classes, a Facade or Factory design pattern, or functions from a module. All three will utilize many internal functions, but will only expose one function to use them. This can sometimes ensure as you add things and fix bugs, the consumers don't have to change their code when they update to your latest code. Side effects can still negatively affect this.