anchor.diff:   * Abstract state in a state machine for scanning keywords.
    */
   abstract class KeywordState {
  +  KeywordState(this.keyword);
  +
     bool isLeaf();
     KeywordState next(int c);
  -  Keyword get keyword;
  +  final Keyword keyword;
   
     static KeywordState _KEYWORD_STATE;
     static KeywordState get KEYWORD_STATE {
  
positive.code:  */
  class ArrayKeywordState extends KeywordState {
    final List<KeywordState> table;
    final Keyword keyword;
  
    ArrayKeywordState(List<KeywordState> this.table, String syntax)
      : keyword = (syntax == null) ? null : Keyword.keywords[syntax];
  
    bool isLeaf() => false;
  
  
negative.code:  * A state that has no outgoing transitions.
   */
  class LeafKeywordState extends KeywordState {
    LeafKeywordState(String syntax) : super(Keyword.keywords[syntax]);
  
    bool isLeaf() => true;
  
  