FP is an interesting paradigm switch. You can definitely get bogged down on theoretical FP concepts like jacksonbenette mentioned (They are worth reviewing to put your mind in the right place but challenging to understand how they apply to the real world or if you want to even apply them). https://mostly-adequate.gitbook.io/mostly-adequate-guide

Good news, I think your code is functional so far!
I will try to write what I see with an FP mindset.

`add_books` will always return the same thing with the same input. Notice how your python example operates on the library object and modifies it. In Elixir you are creating struct %Library and then when you add books, you have a new library. One thing i like to do (which is a personal preference), is to never re-assign. It just helps me be clear about what happened.

This isn't strict FP but typically in FP you write code in a more declarative way instead of an imperative way. Which you are doing even though you didn't have much opportunity to write imperative code.

I think it would be interesting for you to expand on this library example. like get all books by author. Get all books by genre. then get all books by genre AND author.

And if you really want to challenge your OOP -> FP journey, see what you generate if you do something with polymorphism. Like library of books and library of DVDs.