Hi I would also like to congratulate Conal and everyone else involved in the Reactive framework and libraries for the new release. Amazing work! I have finally managed to do more than read about it, and actually toy with some Reactive programming :-) It seems great fun, and the learning curve is not as steep as it might seem at first. I mostly played with Test.hs inside the reactive-fieldtrip adapter, and I have encountered a few issues: A. It seems that when changing spinningG to scale according to time, it becomes extremely slow very quickly. B. The lplace demo itself is also extremely slow, whereas other demos seem to be fine/quick. It might be buggy, and not extremely slow, its taking so long to react that I am not sure what is happening. C. Stylistic question/comment: The (Anim a) type (UI -> Behavior a) is a Reader Functor/Applicative/Monad. I see it used as a Functor in various examples, but it seems that there's no use of the Applicative/Monad of the reader, is this intentional? I find it a bit awkward that it passes the "env" arg to all of the stuff its combining... The example even used an undefined error value in place of the env in some cases, suggesting that it is a burden to pass it around. Why not encourage the implicit passing of the env everywhere via the reader Applicative? Eyal