Active Annotations finally bring the preciseness of the specification into my code.

Usually.xtend

Xtend:

@Usually
def doStuff() {
  println("This usually doesn't fail")
}

generated Java:

public void doStuff() {
  if (System.currentTimeMillis() % 42 == 0) {
    throw new IllegalStateException("Well, usually...");
  }
  System.out.println("This usually doesn't fail");
}