Late response, but yes, you are completely right. You wouldn't use either implementation whether you're using Python or Haskell; you'd use what you said, because that's both the most obvious and the most performant method of achieving the goal. It's just a fun exercise to show that the version using a lazy map is equivalent to the obvious thing. Some people find it mind-bending and satisfying in the same way some people might find bit-twiddling hacks cool, or math nerds might find any of these mathematical identities cool.

https://math.stackexchange.com/questions/505367/collection-o...