public function tokenize($string)
    {
        $line     = 1;
        $position = 1;
        $tokens   = array();

        while (strlen($string)) {
            foreach ($this->expressions as $rule) {
                if (!preg_match($rule['match'], $string, $match)) {
                    continue;
                }

                // Remove matched string from input
                $string = substr($string, strlen($match[0]));

                // Update position in file
                $line += substr_count($match[0], "\n");
                if (($pos = strrpos($match[0], "\n")) !== false) {
                    $position  = strrpos($match[0], "\n") + 1;
                } else {
                    $position += strlen($match[0]);
                }

                // Skip irrelevant rules
                if (in_array($rule['type'], $this->ignoreTokens)) {
                    continue 2;
                }

                // Add all other rules including their match to the token array
                $match = $this->removeNumericKeys($match);
                $tokens[] = new Token($rule['type'], $line, $position, $match);
                continue 2;
            }

            throw new \RuntimeException(
                "Could not parse string: '" . substr($string, 0, 20) . "' in line $line at position $position."
            );
        }

        $tokens[] = new Token(self::T_EOF, $line, $position, null);
        return $tokens;
    }