> So I immediately hit a block as I'm struggling to understand why I need the notion of a Functor to understand what in the end looks like just lazy mapping of

> So I immediately hit a block as I'm struggling to understand why I need the notion of a Functor to understand what in the end looks like just lazy mapping of a function over a stream. You don't, for this one example. You don't, for any one example. But if you keep looking, you'll find more and more of these examples of functors embedded in the code you are already writing. You need the notion of functor when you want to abstract over all of these examples, or generalize one of your examples to handle things that it couldn't before.