public function nextIs($tokenName, $ignoreWhitespace = false)
    {
        $i = $this->index+1;
        $len = count($this->tokens);
        while ($i < $len) {
            $tok = $this->tokens[$i][0];
            if ($ignoreWhitespace && $tok === 'WHITESPACE') {
                $i++;
            } else {
                return $tok === $tokenName;
            }
        }
        return false;
    }