/**
   * Check whether an expr or opArg is level correct, and if so,
   * calculates the level information for the expression. Returns
   * true iff this is level correct.
   */
  public boolean levelCheck(int iter) {
    /***********************************************************************
    * This is called for a node n to calculate the level information for   *
    * n and all its descendants.  It should be overridden by each          *
    * subclass to perform the level checking appropriate for the class of  *
    * node.  It is this method that computes the objects levelData field.  *
    *                                                                      *
    * The method returns true iff n and all of its descendants are level   *
    * correct.  However, this value is apparently never used.  Instead,    *
    * level errors should be reported using errors.addError.               *
    *                                                                      *
    * To handle recursive definitions, level checking must be performed    *
    * more than once.  To handle this, successive calls are with larger    *
    * values of iter.                                                      *
    *                                                                      *
    * Note: Except for those objects whose level values are initialized    *
    * when the object is constructed, levelCheck must be called on an      *
    * object before any of the methods getLevel(), getLevelParams(),       *
    * getLevelConstraints() getArgLevelConstraints(), or                   *
    * getArgLevelParams() is called on it.  This is not a concern for      *
    * tools that use the level information provided by SANY. However, it   *
    * is crucial that this requirement be obeyed during level checking.    *
    ***********************************************************************/
      throw new WrongInvocationException("Level checking of " + kinds[this.getKind()] +
                 " node not implemented.");
   }