This post was inspired by this post on William Cook's blog.
I've been thinking a lot about GUIs lately, and I think model-view-controller is a very good idea -- but one that existing languages do a poor job supporting. Smalltalk deserves credit for making these thoughts possible for Trygve Reenskaug to express, but it's been over 30 years; we really ought to have made it easy to express by now.
Now, the point of a controller is to take low-level events and turn them into high-level events. Note that "low-level" and "high-level" ought to be relative notions -- the toolkit might give us mouse and keyboard events, from which we write button widgets to turn them into click events, from which we write calculator button turns into application events (numbers and operations).
However, in reality new widgets tend to be extremely painful to write, since it usually involves mucking around with the guts of the event loop, and so people tend to stick with what the toolkit gives them. This way, they don't need to understand the deep implementation invariants of the GUI toolkit. As a result, they don't really build GUI abstractions, and so they don't need separate controllers. (A good example would be to think about how hard it would be to write a new text entry widget in your toolkit of choice.)
So I see the move from MVC to MV as a symptom of a problem. The C is there to let you build abstractions, but since it's really hard we don't. As a result new frameworks drop the C, and just grow by accretion -- the toolkit designers add some new widgets with each release, and everybody just uses them. I find this a little bit sad, honestly.
As you might guess from this blog, I find this quite an interesting problem. I think functional reactive programming offers a relatively convenient model (stream transducers) to write event processors with, but we have the problem that FRP systems tend towards the unusably inefficient. In some sense this is the opposite problem of MVC, which can be rather efficient, but can require very involved reasoning to get correct.
This basically leads to my current research program: can we compile functional reactive programming into model-view-controller code? Then you can combine the ease-of-use of FRP, with the relative efficiency[*] of the MVC design.
IMO, the system in our LICS paper is a good first step towards fixing this problem, but only a first step. It's quite efficient for many programs, but it's a bit too expressive: it's possible to write programs which leak rather a lot of memory without realizing it. Basically, the problem is that promoting streams across time requires buffering them, and it's possible to accidentally write programs which repeatedly buffer a stream at each tick, leading to unbounded memory use.
[*] As usual, "efficiency" is relative to the program architecture. MVC is a retained mode design, and if the UI is constantly changing a lot, you lose. For things like games, immediate mode GUIs seem like a better design to me. In the longer term, I'd like to try synthesizing these two designs, For example, even a live-document app like a spreadsheet or web page (the ideal cases for MVC) may want to embed video or 3D animations (which work better in immediate mode).