To be pedantic, the world is not mutable, rather, it is a process undergoing a continuous transformation. Also, machines deal with data - which is encoded info

To be pedantic, the world is not mutable, rather, it is a process undergoing a continuous transformation. Also, machines deal with data - which is encoded information about the world. So when we say that a thing 'changes' in the world, what we're actually saying is that at time T, something happens to the world and from then on, the data we read back is different. 'Something happened' is new information which is added on top of the state of the world at time T-1. Eg. the user e-mail does not 'change' to be come X, but rather, it used to be Y, then the user changed it to X on 1st of May. So we can generalize that the world is a function `f` of some state combined with extra data of what happened at time T, giving us the state at T.