In the case of this video, you aren't missing much. It's deliberately 'dense', according to the author, but the concept is simple. Almost any app will involve

In the case of this video, you aren't missing much. It's deliberately 'dense', according to the author, but the concept is simple. Almost any app will involve some imperative code, but using pure functions within that, where possible, makes it easier to reason about what is going on. That's all there is to it. https://en.wikipedia.org/wiki/Referential_transparency https://en.wikipedia.org/wiki/Referential_transparency