Xtext 2.1 and JVM Languages

Earlier this year, Xtext 2.0 was released. It brought the new Xtend language for transformation and code generation (and to some extent, a replacement for Java). It also included Xbase, an expression language which you could include into your own DSLs by inheriting from Xbase. At the time, I had two complaints about Xbase and the way you would use it. First, Xbase is highly integrated with the JVM. If you wanted to write a DSL that targetted for example C, the provided infrastructure around Xbase wasn't of much help. The other complaint I had was that the integration of Xbase with your own DSL was quite a lot of work to pull off. You had to write all kinds of artifacts to get it done. It was a lot of low-level work.

With Xtext 2.1 things have changed and really become interesting! My first complaint is still true: Xbase is still very much tied to the JVM, so if you wanted to build a DSL that had nothing to do with the JVM, you'd probably be better off building your own grammar and using the Xtext typesystem framework to define typing rules. However, building your own JVM-based language has become impressively simple: you define a grammar (which embeds Xbase in places, e.g. for expressions or operation implementations. The second artifact you build is a little model transformation that maps your new concepts to JVM concepts. This is conceptually similar to generating Java code. However, you don't generate text, but you instantiate JVM objects (classes, methods, fields, etc.). From this mapping information, Xtext then derives everything necessary to derive a generator! This is really pretty neat! The JVM mapping can be expressed very concisely using the new builder-style support in Xtend. Also note that for implementation code (Xbase stuff) there is of course already a generator to Java as part of Xbase, so you don't have to deal with this aspect at all.

So, if we just accept that Xtext and Xbase is mainly targetted to JVM-based languages, then the new Xtext 2.1 stuff is really a big step forward and pretty impressive!  permalink