PHP Events callback methods

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$callbacks = null;

function addEvent($type, $callback)
{
	global $callbacks;
	
	if (empty($callbacks))
	{
		$callbacks = array();
	}
	
	if (empty($callbacks[$type]))
	{
		$callbacks[$type] = array();
	}
	
	$callbacks[$type][] = $callback;
}

function fireEvent($type)
{
	global $callbacks;
	
	if (!empty($callbacks[$type]))
	{
		foreach ($callbacks[$type] as $callback)
		{
			call_user_func($callback);
		}
	}
}

function removeEvent($type, $callback)
{
	global $callbacks;
	
	if (!empty($callbacks[$type]))
	{
		foreach ($callbacks[$type] as $i => $found)
		{
			if ($callback == $found)
			{
				unset($callbacks[$type][$i]);
				break;
			}
		}
	}
}

$callback = function(){
	echo 'hello!';
};

addEvent('speak', $callback);

fireEvent('speak');

removeEvent('speak', $callback);

fireEvent('speak');