[rules-users] function in guided decision table

Hello everyone. I'm using the latest kie workbench and I have created a guided decision table. I want to create a function and call it from an action of the guided decision table. The problem is that I cannot find a way to declare the function and make it visible from the guided decision table. I have tried declaring it in a drl file, as well as in a dsl definition without success (the error is that drools cannot analyze the function call expression). Has anyone solved this issue before? Kind regards.