Reactive is getting more mature, but still does not support “feedback” behaviors (a bug), and still does not support true first-class Behaviors (an essential limitation); meaning you cannot efficiently put a Behavior in a data structure and save it for later use. By observing the reactive mailing list, this limitation is proving unimportant; still plenty of things are possible. But I am a stubborn, hubristic person, and I simply insist on Fran semantics (Behavior & Future) with first class Behaviors.
I have tried and I have tried, and I am quite convinced that the Fran semantics are not implementable lazily and efficiently in Haskell. I think I have come up with a garbage collector extension that would allow it, but I’m not going to pursue it. Knowing that such an extension exists is important to me, however, as I see hardware such as The Reduceron playing a big role in the future. The IO monad is not going to fly in a reduceronian world.
My impatience for a functional reactive game and UI library is growing. I could have made one in Fregl, but I became convinced that Fregl was too inefficient, and that I required weak-reference-free laziness to make it efficient. In retrospect, however, Fregl was inefficient for many more reasons than simply its eagerness. I am thus throwing aside my laziness requirement, and am now setting out to make a very efficient eager FRP library with Fran semantics.
Perl hackers know the three virtues: laziness, impatience, and hubris. I find it amusing that the one I’m having to throw away in a lazy language is laziness itself.