Christopher Howard
Hi. I'm trying to understand what Functional Reactive Programming is, or, more properly, what distinguishes it from "regular" functional programming, and what it would look like if I were to program in a "FRP Style", i.e., without some mysterious FRP module hiding the details. After reading a bunch of links and even looking at some source code I'm still not clear on this.
If I program in an event-based style, and have data structures updating over time, with some data structures dependent on others for their values, and I use a functional language, is that FRP? Or is there some essential element I'm missing here?
Yes. FRP is about domain-specific languages that capture the notion of time-varying values. Let me take Netwire 4 as an example. It's not on Hackage yet, so you may want to grab it using darcs: darcs get http://darcs.ertes.de/netwire/ Imagine you have a simple GUI label that displays the number of seconds passed since program start. In an event-based model this is actually quite a complicated task. You would have to create a label and update it all the time using some form of timer/idle event. In Netwire you write: myLabel = time Now let's say you want to have the same GUI, but the time should start at 10 and pass twice as fast, so you actually want to display twice the number of seconds passed plus 10: myLabel = 10 + 2*time Imagine you want to display the string "yes" in a label: myLabel = "yes" Now let's say you want to display "yes", when the space key is held down and "no" otherwise: myLabel = "yes" . keyDown Space <|> "no" You want to display time while pressed and "Press space" while not: myLabel = fmap show time . keyDown Space <|> "no" You want to display "yes" every other second and "no" otherwise: myLabel = "yes" . holdFor 1 (periodically 2) <|> "no" Imagine doing that with event-based code. Summary: FRP is about handling time-varying values like they were regular values. Greets, Ertugrul -- Not to be or to be and (not to be or to be and (not to be or to be and (not to be or to be and ... that is the list monad.