Category: yesod

For BayesHive, we have a fairly big Yesod web application plus a lot of client-side JavaScript code. We've gone through a couple of iterations of how we organise all this. We started with a quick and nasty manual approach to chaining state between different pages of the app. That was pretty horrible. Then, as described in an earlier article, we switched to using AngularJS in the browser, which made the JavaScript side of things much nicer, along with Michael Snoyman's yesod-angular module for managing the interaction between the client and server. Eventually, we found that Angular's default routing provider wasn't flexible enough for our needs in the browser (we have quite a few "wizard"-type stateful interactions, plus a fairly complex dashboard with lots of more independent states).

So we decided to switch over to using the Angular ui-router state-based routing system. This is pretty good and is definitely flexible enough for our current needs. It allows you to define a hierarchical structure of UI states, cleanly controlling transitions between states and assigning URLs to states to allow good interaction with the browsers back and forward buttons and to allow bookmarking of application states. The only problem? Not something that the yesod-angular code supports...

For the past few months, I've been spending most of my working hours on BayesHive, the brainchild of Tom Nielsen, CEO of OpenBrain. This is a web platform for doing Bayesian data analysis, intended to make these powerful methods more accessible for scientists and other data analysts.

We opened the system to some alpha users a while ago, but this week we've decided we're ready for wider beta testing, for people to have a look, kick the tyres and tell us what they think.

I've mostly been working on the web app part of the system, but in this post I want to talk a little bit about the general idea behind the system and the Bayesian approach to statistics. (As far as BayesHive goes, the system is made up of a reasonably complicated single page web app using the AngularJS framework, a Yesod server process to deal with the management of documents, data and models, and a model compiler and inference engine that does all the clever stuff.)

Michael Snoyman recently had a blog post about composability in the Yesod web framework for Haskell, where he responded to comments about it being difficult to build reusable components for Yesod by, well, building one. I'm pretty much a newbie with Yesod, but the composability aspect of things had never looked too difficult to me, so I thought I'd also have a go at the same kind of exercise.

I decided to implement a slider form field, using one of the nicest jQuery-based slider widgets I've found. All the code for this example is available as a Gist. I'll follow the usual convention here of putting more or less all of the code in the blog post too.