[wynand]

I'll hazard a possibly bad answer.

MVC is not inherently OO - it's more about sending messages which, although a feature of modern OO (Alan Kay even said that he should have called OO Message-Oriented programming), is not its defining feature (as we see it used today).

Since the Model, the View and the Controller are just continually processing and sending messages, you could easily implement them as processes (say as in Erlang). A processes's state is then retained in immutable structures passed to recursive invocations of its main message loop (sorry if this sounds opaque - I'd recommend seeing how it's done in Erlang).

Another GUI approach to FP that is being researched is functional reactive programming. There is a neat Javascript implementation called FlapJax. You could probably argue that FRP is a generalization of MVC (though I'll hedge my statement since I'm not 100% sure of this).