How Do I Compile a Type System?

Each process has its own state and its own message. You have to be responsible to pattern match on those different versions of the messages you get in. But you also have vergins of your state. So maybe i have a user, and instead of having a email address associated that user, in this process manages the state for a user. And so there's call back gets invoked when it says, oh, i see you've got a new piece of code here. We're going to take that state. I woing to give you that old state, here's the version, and go from version, version one to version two.