Modules are declared similarly as classes. Their declaration include:

• A name
• An optional list of attribute
• An optional list of class/interfaces that are extended/ implemented
• An instantiation declaration

Modules are declared in XL with the keyword module (different from the java keyword module).

module A(int attr1, Object attr2) extends N { /* body */ } ==> ;

Only the Name is non optional in the declaration. Thus, the smallest module declaration is:

module A;

This declaration is equivalent to:

class A extends N {
}

The declaration uses an implicit superclass N which is determined by the annotation @DefaultModuleSuperclass of the innermost enclosing declaration which has such an annotation. RGG files have default annotations, one of these is the @DefaultModuleSuperclass. Its value is Node.

A list of typed arguments can follow the Name. This list is used as declaration of the attributes of the module.