The Revisitor pattern is a language implementation pattern that enables independent extensibility of the syntax and semantics of metamodel-based DSLs, with incremental compilation and without anticipation. It is inspired by the Object Algebra design pattern and adapted to the specificities of metamodeling.

On top of the Revisitor pattern, we introduce ALE, a high-level language for semantics specification of metamodels that compiles to Revisitors to support separate compilation of language modules.

ALE is tightly integrated with the Eclipse Modeling Framework (EMF) and relies on the Ecore meta-language for the definition of the abstract syntax of DSLs. Operational semantics is defined with ALE using an open-class-like mechanism. ALE is bundled a set of Eclipse plug-ins.

1. Download an Eclipse IDE for Java and DSL Developers (Neon.3) for your platform: http://www.eclipse.org/downloads/packages/eclipse-ide-java-and-dsl-developers/neon3
2. Install the ale plugins using the update site: http://gemoc.org/ale/revisitors/updatesite/. Follow the procedure and select every plugin available.
3. Restart your Eclipse environment
4. You're all set!

The ALE plug-ins provide two main operations to the user:

• On an Ecore (*.ecore) metamodel: Right click -> ALE -> Generate Revisitor interface generates the corresponding Revisitor interface in the src directory of the current project
• On an ALE (*.ale) file: Right click -> ALE -> Generate Revisitor implementation generates the corresponding Revisitor implementation in the src directory of the current project
• (note that Revisitor implementations depend on Revisitor interfaces and will not compile otherwise)

The ALE update site can be rebuilt from scratch using the ale.p2updatesite project.

After importing the projects into eclipse, open the ale.p2updatesite/site.xml file and click "Build All". This will publish the update site content within the ale.p2updatesite directory.