public void addIndex(Expression expr) {
if (expr.getParent() != null) throw new NotAnOrphanException();
children.add(expr);
expr.setParent(this);
}
/**
* Sets the nth index expression of this array access.
*
* @param n The position of the index expression.
* @param expr The expression to use for the index.
* @throws IndexOutOfBoundsException if there is no expression at that position.
*/
public void setIndex(int n, Expression expr) {
if (expr.getParent() != null) throw new NotAnOrphanException();
children.set(n + 1, expr);
expr.setParent(this);
}