Is O.O. Good for Simulation?

Eric Normand: O.O. is good for simulation, but it's very hard in simulation when you have mutable values to ask questions about hypotheticals. In one of the two main ways that are pretty general are keeping a history of states and keeping ahistory of commands. This allows you to do stuff like undo. And it lets you see how you got there, you know? It uses a function which lets you do a reduce to get the current state. You can always rebuild the current state if you need it.