> The classic example is a list or array. You don't add a value to an existing list. You create a new list which consists of the old list plus the new value. [1]

Getting back to this, though - where would this be useful? What would do this?

I'm not getting why having a new list that's different from the old list, with some code working off the old list and some working off the new list, is anything you'd ever want.

Can you give a practical example of something that uses this?

Why doesn't the list just have a mutex?