A story about rubber ducks and functional programming

Once upon a time, I wanted to get a rubber duck. One rubber duck. I spent a lot of time looking for a perfect yellow rubber duck not representing any character and finally, I have found and bought it.

Later I accidentally found a much better rubber duck. I bought it also. That's one more rubber duck than I but I wasn't cruel enough to throw first one away. A big mistake.

First, everything was fine. One duck was small and squeaky, another one was big and didn't make any noises at all so I called them Jay and Silent Bob. But two ducks started breeding, everyone thought I'm collecting rubber ducks now so they started presenting me more and more. Now I have many more rubber ducks that I wanted to have.

Moral: avoid side effects.