I don't get it. You haven't used map in void context. Also, I'm not convinced that you haven't purposefully
written your code inefficiently just to prove that map
is useful. Why do you have the intermediate grep when
an if in the for loop would do just fine? Sure, copying
lists around is *fairly* cheap, but we come to my
original point: Did you actually take a step back before
designing your code, to ensure that it works best? Or
did you just string map and grep together until it
worked the way you wanted it to?