I saw David Nolen's wonderful Clojure West talk today, and it inspired me immensely. Specifically, the two demos he showed towards the end: zenrise, an interface builder by @sgrove, and session, a Mathematica-like notebook by @kovasb, both written in ClojureScript using Om.
Imagine this. You boot up your Nexus 7 or (I wish) iPad, and instead of iOS or Android, you see a system like Firefox OS, built on HTML web components. On top of the core system apps, there are two more applications: Editor, and Notebook.
Editor is a touch IDE, designed to allow you to model your problem with reusable components. Notebook is a medium to quickly sketch out and simulate ideas, like Mathematica. I'll focus on Editor:
It's an IDE that allows programs to be built out of Om components, through which data flows via clojurescript core.async channels. We use something that looks a lot like Interface Builder to layout our component-based UIs with declarative constraints (enforced with Cassowary) instead of markup and stylesheets, and we can see through the interface to the data flowing between our components.The flow of data is detected using clojure tools.analyser and then visualized for the user, enabling them to pipe together components like unix shell scripts, but in more than one dimension and with direct manipulation. Even better: these components don't need to have any knowledge of each others' CPIs. I say "CPI" and not "API" because these component programming interfaces attempt to solve the "communicating with aliens" problem: components send messages to each other to figure out what shape the shared interface they can satisfy is using Prismatic's schema, and pattern match on those using core.logic to offer capabilities to each other.
It can get better. When we need a component we haven't built yet or isn't provided by the system, we look it up in a global repository of components, which also communicate via discoverable, loosely-coupled CPIs. When we're satisfied with our program, we serialize the data structure describing its UI to storage, and it's immediately ready to run on our tablet. We've designed and implemented it from the ground up with direct manipulation, and its interface can scale to different devices because we designed it using constraints instead of hardcoding values. We used touch to wire together components, to directly manipulate flowing data, and saw the results rendered in real-time! We solved the code reuse problem by using components designed to dynamically discover each others' capabilities and degrade gracefully when data they are provided doesn't exactly meet the specified shape.