svoid nlLogic_visit(IfThen rule, VF1<O> visitor) {
  if (rule == null) ret;
  callF(visitor, rule);
  nlLogic_visit(rule.in, visitor);
  nlLogic_visit(rule.out, visitor);
}

svoid nlLogic_visit(Exp e, VF1<O> visitor) {
  if (e == null) ret;
  callF(visitor, e);
  if (e cast And) {
    nlLogic_visit(e.a, visitor);
    nlLogic_visit(e.b, visitor);
  } else if (e cast ExpNot)
    nlLogic_visit(e.a, visitor);
  else if (e cast Func)
    nlLogic_visit(e.arg, visitor);
}

svoid nlLogic_visit(Collection l, VF1<O> visitor) {
  for (O o : unnull(l)) nlLogic_visit(o, visitor);
}

svoid nlLogic_visit(O o, VF1<O> visitor) {
  if (o cast Exp) nlLogic_visit(o, visitor);
  if (o cast IfThen) nlLogic_visit(o, visitor);
  if (o cast Collection) nlLogic_visit(o, visitor);
}