Added fancy tree representation

        }

    }

    public function printTree($indent=0) {

    public function printTree($indentStr='', $isLastChild=false) {

        static $stack_depth = 0; global $STACK_LIMIT;

        if (++$stack_depth > $STACK_LIMIT) {

            throw new RuntimeException('Stack limit exceeded.');

        }

        try {

            if ($this->definition() !== null) {

                echo str_repeat('  ', $indent) . $this->definition()->name() . "\n";

                echo $indentStr . '+-' . $this->definition()->name() . "\n";

            }

            $extraIndentStr = ($isLastChild ? '  ' : '| ');

            $argIdx = 0;

            foreach ($this->args() as $arg) {

                ++$argIdx;

                if ($arg instanceof TokenInstance) {

                    echo str_repeat('  ', $indent + 1) . $arg;

                    echo $indentStr . $extraIndentStr . '+-' . $arg;

                } else {

                    $arg->printTree($indent + 1);

                    $arg->printTree($indentStr . $extraIndentStr, $argIdx == count($this->args()));

                }

            }

        } finally {