But most interesting web UIs are not static->dynamic; they instead involve dynamic and circular dependencies. Pressing the "add new todo" control doesn't just dynamically affect the display, it also creates new controls that need to get added into the set of observable things that affect the display. This idea, of modifying existing observables to include new observables, is somewhat problematic. In examples I've seen, it ends up leading back to code just as unfortunate as imperative callbacks.
If you can use Bacon to create an entry for TodoMVC [3] showing how to have dynamic->dynamic dependencies, I'll be sold.
Traditional FRP has two main concepts: behaviors, which are values that can change continually, and stream of events. Scanning over this blog post, these ideas correspond roughly to Properties and EventStreams respectively in Bacon.js.
Event switching is just having an event stream that itself contains behaviors. There's a great blog post[1] about this using Reactive Banana and Haskell.
[1]: http://apfelmus.nfshost.com/blog/2012/09/03-frp-dynamic-even...
Most of the post is fairly Haskell-specific, talking about the type system, but the basic idea should be applicable here as well.
The running example is a bar tab. You want to be able to create new entries in the tab, which are just text entries that give you a price. So you would create something like
entries :: Event [Behavior Price]
I'm not sure how other libraries support this dynamic event switching though. My understanding is that it is somewhat tricky to implement efficiently.
Helpful diagrams: https://github.com/raimohanska/bacon.js/wiki
https://github.com/pyykkis/todomvc/blob/bacon-transparency-r...
More about event delegation here: http://api.jquery.com/on/
$('#container').asEventStream('click', '.someclass')
If an element with someclass is ever added as a child of #container, clicks on it will fire events. This is true even if the someclass element is added after the asEventStream call.
In Flowdock, there is a form that automatically validates parts of the data in JS while needs to confirm other parts with server. During server-side validation, a loading indicator is shown and success enables the submit button. Using Bacon, it has been easier to focus on the logic instead of handling state. But the logic is quickly quite hairy, indeed.
Japsu pointed out that there is a TodoMVC implementation with Bacon and Backbone, but it'd certainly be interesting to see/do a pure-FRP implementation.
http://rstudio.github.com/shiny/tutorial/#dynamic-ui (scroll down to reactiveUI)
An example: http://glimmer.rstudio.com/winston/dynamic_ui/ https://gist.github.com/4211337
This looks pretty similar to a .NET library called Rx (Reactive Extensions). We're using it in a MonoTouch iOS app and I found it to solve some problems in a very convenient way. If you used functional style in your code, you know it shines in mapping/filtering/aggregating/reducing sequences of data. In .NET LINQ sequences have type of IEnumerable. You can think of Rx's IObservable as of IEnumerable's odd twin brother. The main difference is you IEnumerable is “cold” by its nature: it produces new items when you ask for them by calling MoveNext(). It doesn't do anything by its own. It's also synchronous.
IObservables, however, can both be cold and hot, i.e. they can yield items without being asked to. It's like IEnumerable but with “don't call me—I'll call you” approach. Because of this, it doesn't have to be synchronous. Long processes that emit one item at a time, which may later be transformed, processed in batches, throttled, etc, benefit from being expressed via IObservable. The benefit I found is you can easily switch between different asynchronous data source implementations.
For example, it's trivial to write an IObservable wrapper around iOS Photo Library that will yield one item at a time. Then you can write a function that compares cached items in array with new items that arrive from photo library, and return IObservable of “differences” between cached and new data. Then you group those differences using built-in methods into batches—and feed them to UICollectionView so it can animate the updates as the application receives them from system API.
Then you just write another IObservable implementation for getting photos from Facebook, and wrap it in a function that will pre-fetch their thumbnails before yielding them. It is also an IObservable. You already implemented updating collection view, so you just plug in your new asynchronous data source and that's it.
Need to implement a Dropbox file picker? You already implemented collection view logic, diff logic and prefetching images, so you just need to wrap Dropbox folder fetch API in an IObservable, and merge IObservable-s from nested folders.
On top of that, you can add some caching, and magically it will work for any data source.
- Microsoft creates Rx (Erik Meijer, one of the haskell developers)
- Microsoft releases RxJS, a js implementation of Rx
- Juha Paananen gets fed up with some RxJs wtfs (http://nullzzz.blogspot.com/2012/01/things-you-should-know-a...) and makes Bacon.js
Boasts of realtime, 2-way bindings between any JS object.
Sure, everybody loves bacon – except vegans, vegetarians, Jews, and other swine-shunning cultures – but I really don't want to be thinking about bacon when I'm programming. Nor do I want to evoke the smell, taste, and unhealthiness of bacon, nor the dirtiness of pigs, in the minds of people I talk to about Bacon.
Largely for this reason I will probably not try, use, or try to get my friends to use Bacon. Please consider changing the name, perhaps to something that evokes the conceptual spirit of the project, because I'd like to see more people adopting FRP techniques.
I often browse google for solutions, but I miss a lot of interesting, popular, relevant blogs when the project name is a common noun utterly unrelated to the project. I recognise naming is difficult, but it makes it hard to find popular, interesting, relevant blogs when I have to swim though the mass of web pages that use the common noun.
Sometimes I wish more projects would call themselves FRP20x14qq77aciq or something approaching uniqueness. Almost like 0x10c. At least until we get some semantic tags to say "and I mean something to do with programming and definately not anything to do with what this common noun means 99.9999% of the time".
Maybe a better name would be pigfucker.js so as to more equitably offend everyone. But that's probably not necessary since I bet bacon.js was named after Francis Bacon anyway - right nullzzz? :-)
How would you cool yourself if you didn't have sweat glands? Blaming pigs for being unhygenic is like blaming cancer patients for not having hair.
I happen to find Satanic imagery a bit cool, so I probably wouldn't mind, but others might. Would you use a project called Vomit.js? Diarrhea.js? Ebola.js?
> And if your dad was killed by a gnu, you would only use BSD's?
Um, perhaps?
> I hope you like apples and windows
Apples and windows are relatively benign objects without disturbing imagery attached to them.
> How would you cool yourself if you didn't have sweat glands? Blaming pigs for being unhygenic is like blaming cancer patients for not having hair.
Who's blaming pigs? Pigs, their mud, and their parasites are simply unsavory to think of for many people. Likewise, bacon itself is so savory that my mouth starts watering and I can't stop thinking about salty fat. For others, bacon is either disgusting or something to be shunned.