Implementing Domain-Specific Languages with Xtext and Xtend

Dealing with super

As a final feature, we add the mechanism for invoking the implementation of a method in the superclass by using the keyword super. Note that super should be used only as the receiver of a member selection expression, that is, it cannot be passed as the argument of a method. Following the practice "loose grammar, strict validation", we do not impose this at the grammar level. Thus, we add the rule for super as a terminal expression:

SJTerminalExpression returns SJExpression:
   ...
   {SJSuper} 'super' | ...

and we add a validator rule that checks the correct super usage:

@Check
def void checkSuper(SJSuper s) {
  if (s.eContainingFeature != SmallJavaPackage::eINSTANCE.SJMemberSelection_Receiver) error("'super' can be used only as member ...