gistfile1.php

class Callbacks
{
	protected $_callbacks = array();

	protected function _add($name, $callback)
	{
		$this->_callbacks[$name] = $callback;
	}

	protected function _remove($name)
	{
		unset($this->_callbacks[$name]);
	}

	public function call($name, $parameters)
	{
		return call_user_func_array($this->_callbacks[$name], $parameters);
	}

	public function __construct($callbacks = null)
	{
		# overwrite callbacks

		if ($callbacks !== null)
		{
			$this->_callbacks = $callbacks;
		}

		# define standard callbacks

		$this->_add(
			"return",
			function($value) {
				return $value;
			}
		);
	}
}

$new = new Callbacks();
echo $new->call("return", array("hello world"));