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);