abstract sclass WordTokRule extends Attractor implements RuleOnTok, RuleOnString {
  S pattern; // example sentence
  Set<S> vars; // list of the variable words in the sentence
  bool debug;

  transient LS tokPat; // parsed pattern
  transient SS map; // not null if there is a match
  
  *() {}
  *(S *pattern, S... vars) { this.vars = litciset(vars); }
  *(S *pattern, Set<S> *vars) {}
  
  LS tokPat() {
    if (tokPat == null) tokPat = wordTok(pattern);
    ret tokPat;
  }
  
  public bool matches(ExtS s) {
    process(s);
    ret matched();
  }
  
  public bool matches(S s) {
    process(s);
    ret matched();
  }
  
  public void process(ExtS s) {
    processTok(extLift(s, wordTok(s!));
  }
  
  public void processTok(Ext<LS> tok) {
    map = nullIfContainsKeysOtherThan(gazelle_zipTwoTokenizationsToMap(tokPat(), tok), vars);
    if (debug) print(pattern + " + " + join(tok) + " => " + map);
  }
  
  bool matched() { ret map != null; }
  S getVar(S name) { ret getOrKeep(map, name); }
}