I think this is reading too much into the toy example, but I want to mention a drawback of your rewrite: in the original, map and filter made it clear that all

I think this is reading too much into the toy example, but I want to mention a drawback of your rewrite: in the original, map and filter made it clear that all logic was happening element-wise. By creating functions that take the entire list as input, this has been obscured.