Using Event Sourcing in Domain-Driven Design

Each of those commands is like a mutation function and you can reduce that whole sequence and regenerate the current state. This technique is known as event sourcing, where you don't mutate things, you just append to a log of commands that you've run. It makes it really easy to do stuff that's typically considered kind of hard to do, like undo. And if you pop it off and put it onto another stack, you can have undo and redo.