Purity

My car is purely functional: when it runs out of gas, I don't refuel it - I just buy a new car!

My toilet is purely functional: when I take a shit, I don't flush - I just install a new toilet (ah, the smell of purity)!

My girlfriend is purely functional: when I get her pregnant, I don't marry - I just find a new girlfriend!

>>7
When an immutable data structure gets updated, the previous versions of it are still available until garbage collected. That's the whole point of immutability. So if we get a new world every time something changes, then where are the previous worlds?