Nothing about keeping values in functions is ‘non-functional’. That’s like saying that hard coding the quadratic formula inside some function instead of using a lambda as an input is ‘non-functional’. His language in that statement is poorly chosen. I am almost certain he is not implying any action at a distance ‘state’, he is trying to talk about including context for some data inside functions that operate on the data. It would be like hardcoding an ISBN-to-title list inside a function that takes a list of authors and there books as input for processing. I think he’s saying the ISBN-to-title should be a part of the data structure, and storing it inside the functions breaks these rules he has invinted.