anchor.diff:      String string = one;
       if (peek == code) {
         advance();
  -      string = two;
  +      string += two;
       }
       assert(OPERATORS.contains(string));
       return new Token(start, string)..withOp(string);
  
positive.code:         advance();
          if (isExponentSign(peek)) advance();
          if (!isDigit(peek)) error('Invalid exponent', -1);
          simple = false;
        } else {
          break;
        }
        advance();
      }
      String string = input.substring(start, index);
      num value = simple ? int.parse(string) : double.parse(string);
  
negative.code:     if (!buffer.isEmpty) return buffer.removeLast();
  
      // Skip whitespace.
      while (peek <= $SPACE) {
      if (++index >= length) {
        peek = $EOF;
        return null;
      } else {
        peek = input.codeUnitAt(index);
      }
    }
  
      // Handle identifiers and numbers.
      if (isIdentifierStart(peek)) return scanIdentifier();
  