OOPSLA'04: SeaSide BOF
More reflections on OOPSLA'04.
Before heading to the Vancouver Aquarium for the main social event of the conference I stuck my head into a BOF session about the SeaSide web application framework.
Wow!
SeaSide makes writing web apps startlingly simple and straightforward. In comparison, web app frameworks in the Java world, such as JSP or Struts, and even Ruby on Rails look like dinosaurs.
It does so by turning the conceptual model of most web-app frameworks on its head. Instead of dispatching requests from the client to objects that send back responses, a SeaSide application is written as a single thread of control that sends requests to the user and waits for their response. The application processes response data using the normal control flow statements that programmers are used to: no need for complex configuration files mapping forms to actions to JSP pages, etc etc. I commented, only partly tongue-in-cheek, that the configuration file of a Struts app would be larger than the entire domain logic of a typical SeaSide application doing the same thing.
SeaSide's model of a single thread of control per user is only a conceptual model. Under the hood, SeaSide takes care of what happens when the user navigages backwards and forwards or creates multiple browser windows to interact with the same application. The important thing is that the programmer doesn't have to care: SeaSide maintains the simple programming model as an abstraction above its complex internal implementation. SeaSide also makes it easy to run transactions, compose HTML pages from components and bind HTML links to program actions, all in a natural Smalltalk style.
SeaSide is able to present such a simple API because it takes advantage of "esoteric" features of its implementation language/platform, Smalltalk, such as continuations and closures. Java, in comparison to Smalltalk, is designed on the assumption that programmers using the Java language are not skilled enough use such language features without making a mess of things, and so the language should only contain simple features to avoid confusing our poor little heads. Paradoxically, the result is that Java APIs are overly complex, and our poor little heads get confused anyway. SeaSide is a good demonstration that powerful, if complex, language features make the job of everyday programming easier, not harder, by letting API designers create elegant abstractions that hide the complexity of the problem domain and technical solution.