It's usually event callbacks for actions, although these are often wrapped in a first-class "action" or "command" abstractions, to allow routing different events to the same handler - e.g. both the menu item and the toolbar button.

For views, you either get some form of MVP, with explicitly implemented model interfaces that provide the glue between the views and the object tree they are representing, or data binding that effectively creates that same glue for you. Here's an example from UWP:

https://docs.microsoft.com/en-us/windows/uwp/data-binding/da...

So no, it's not really functional. Quite the opposite - the state is global and mutable, and UX actions that purport change things really change them. That also makes it all very intuitive, though.