类中调用自定义方法如何会Fatal error: Call to undefined function

类中调用自定义方法怎么会Fatal error: Call to undefined function

class Template{

	private $html;
	public $return;

	function __construct($html)
	{
		$this->html = $html;

	}

	function cuts($text,$left,$right)
	{
		$re = rtrim(substr($text,$left,$right-$left));
		return $re;
	}

	function conver()
	{
		$field_left = strpos($this->html,"}}") + 2;
		$field_right = strpos($this->html,"{{endlist}}");
		$tagin = cuts($this->html,$field_left,$field_right);
		print $tagin;
		$param_left = strpos($this->html,"((") + 2;
		$param_right = strpos($this->html,"))");
		$param = cuts($this->html,$param_left,$param_right);
		print $param;

	}

}

Fatal error: Call to undefined function cuts()

为毛会出现这种情况
------解决方案--------------------
$param = $this->cuts($this->html,$param_left,$param_right);