Functional reactive programming
Let's build another kind of application that works in much the same way; one that uses functional programming to react to changes in state. But, this time, the application won't be able to rely on event listeners.
Imagine for a moment that you work for a news media company and your boss tells you to create a web application that tracks government election results on Election Day. Data is continuously flowing in as local precincts turn in their results, so the results to display on the page are very reactive. But we also need to track the results by each region, so there will be multiple objects to track.
Rather than creating a big object-oriented hierarchy to model the interface, we can describe it declaratively as ...