I am reading this book as part of a book club. Just finished chapter 4, and I think the ending section on complexity and why we are doing this was fire.
One topic that came up during book club discussions is that, while this functional approach has its benefits, at the end of the day, we are building APIs or web apps and using Postgres for persistent storage. We rarely have all the entities of interest in memory. How can this functional approach deal with that reality? Eg: When sorting, filtering, and pagination of results have to happen in SQL.