Somewhere in your kermeta code you can call a groovy expression stored in a string. For example:

var args :kermeta::utils::Hashtable<kermeta::standard::String, kermeta::standard::Object> init 
	kermeta::utils::Hashtable<kermeta::standard::String, kermeta::standard::Object>.new
args.put("self", self)
args.put("anotherParam", "someString")
var res1 :kermeta::standard::Object init 
	extern org::kermeta::extra::groovyembedded::GroovyEmbedder.run("println 'Hello GroovyWorld! ' +self' '+anotherParam; return 'foo';", args)
stdio.writeln(res1.toString)

Where args can store object coming from Kermeta and be accessed by the groovy script. In the above sample, self is mapped to a Groovy argument named self, and some string is mapped to a Groovy argument named anotherParam. Both are printed on the standard output. The return can be used to send back data to the Kermeta side in res1 . Another way to send back data would be to simply send an object in an argument and change its content from Groovy.