Nit...Functional means there are no side effects. Side effects are defined, they just aren't easy to reason about. I do want to point out the expected result

Nit...Functional means there are no side effects. Side effects are defined, they just aren't easy to reason about. I do want to point out the expected result of almost every single program an app dev has ever been paid to do is entirely defined as a collection of side effects. For example all I/O is a side effect. I know people have crammed I/O into frameworks and defined them as pure, but that's mostly handwaving.