The code to define rules in a scripting languages is available, however it turned out that using Java was simpler for the current rules. Therefore both letter match example and particle analyzer are currently using Java for rule definition.
This is one thing that does not work directly with Maven
In other to get it to work you have to download jsr223-engines.zip from https://scripting.dev.java.net/servlets/ProjectDocumentList
After that you have to unpack it, and install it into the Maven repository:
mvn install:install-file -Dfile=groovy-engine.jar -DgroupId=org.codehaus.groovy -DartifactId=groovy-engine -Dversion=1.5.1 -Dpackaging=jar
The class ScriptEngineCache establish connection to the scripting engines, by name of the language.
There is a static method call to get a new scripting engine for a scripting language.
Normally it will get the same scripting engine for a scripting language.