On Fri, 2012-03-30 at 09:15 +0300, Michael Snoyman wrote:
First you state that we shouldn't use `union` for the `ePitch` Event, and then you used it for `bOctave`. Would it be more efficient to implement bOctave as someting like:
eOctave :: Event t (Int -> Int) eOctave = filterJust toStep <$> eKey where toStep '+' = Just (+ 1) toStep '-' = Just (subtract 1) toStep _ = Nothing
bOctave :: Behavior t Octave bOctave = accumB 0 eOctave
Yes. Though it's slightly less bad, the case with ePitch was something like 6 appends. It was mostly a case of badly copying the style from the examples and not realizing the examples use event streams from different outside sources. I've adapted the example to use something similar to your eOctave.
Also, I'm left wondering: how would you create a new event stream in the first place? You're telling us to just rely on `eKey`, which is fair, but a great follow-up would demonstrate building it. Looking through the docs I found `newEvent`, but I'm not quite certain how I would combine it all together.
The updated document, which now lives at http://www.haskell.org/haskellwiki/FRP_explanation_using_reactive-banana contains a "Making the example runnable" section which shows how connect the example with the outside world. The short version, regarding the creation of new events, is that you have to do it in two parts. You need newAddHandler in the IO monad to get a (a -> IO ()) function that fires the event as well as something called an AddHandler and fromAddHandler in the NetworkDescription monad to get an event from that AddHandler. It's not possible to get values out of the NetworkDescription monad (without IORef tricks) and events can only be created within a NetworkDescription monad. The newEvent function looks like what you'd want, but because you can't get the event firing function out of NetworkDescription its use is limited. Greetings, Peter Minten