<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi everyone,<div><br></div><div>I am experimenting with various implementation styles for classical FRP. My current thoughts are on a continuation-style push implementation, which can be summarized as follows.</div><div><br></div><div><div><font class="Apple-style-span" face="Courier">> newtype EventT m r a = E { runE :: (a -> m r) -> m r -> m r }</font></div><div><font class="Apple-style-span" face="Courier">> newtype ReactiveT m r a = R { runR :: (m a -> m r) -> m r }</font></div></div><div><div><font class="Apple-style-span" face="Courier">> type Event = EventT IO ()</font></div><div><font class="Apple-style-span" face="Courier">> type Reactive = ReactiveT IO ()</font></div></div><div><br></div><div>The idea is that events allow subscription of handlers, which are automatically unsubscribed after the continuation has finished, while reactives allow observation of a shared state until the continuation has finished.</div><div><br></div><div>I managed to write the following Applicative instance</div><div><br></div><div><font class="Apple-style-span" face="Courier">> instance Applicative (ReactiveT m r) where</font></div><div><div><font class="Apple-style-span" face="Courier">> pure a = R $ \k -> k (pure a)</font></div><div><font class="Apple-style-span" face="Courier">> R f <*> R a = R $ \k -> f (\f' -> a (\a' -> k $ f' <*> a'))</font></div></div><div><br></div><div>But I am stuck on finding a suitable Monad instance. I notice the similarity between my types and the ContT monad and have a feeling this similarity could be used to clean up my instance code, but am not sure how to proceed. Does anyone have an idea, or a pointer to suitable literature.</div><div><br></div><div>Best regards,</div><div>Hans</div></body></html>