anchor.diff:    void emitClasses() {
       assert(classFields.length == classMethods.length);
       for (int i = 0; i < classFields.length; i++) {
  -      currentClass = i;
         emitLn('class X$i ${i == 0 ? "" : "extends X${i - 1}"} {');
         indent += 2;
         emitVarDecls('$fieldName${i}_', classFields[i]);
  +      currentClass = i;
         emitMethods('$methodName${i}_', classMethods[i]);
         emitLn('void run() {');
         indent += 2;
  
positive.code:   void emitTerminal(int depth, DartType tp) {
      switch (rand.nextInt(2)) {
        case 0:
          emitLiteral(tp);
          break;
        default:
          emitVar(depth, tp);
  
negative.code:       emit('(');
        emitExpr(depth + 1, tp);
        emitBinaryOp(tp);
        emitLiteral(depth + 1, tp);
        emit(')');
        return;
      }
  