Simple PHP url dispatcher

//defining what url patterns get mapped into what funcitons.
//if no route is provided 'default' route is used
$routes = array(
	"default" => "sayhello",
	"hello" => "sayhello",
	"sum"  => "computesum"
);
 
/**
*Dispatch function - delegates action to other function and passes parameters to it
*/
function dispatch(){
 
	global $routes;
 
	//stear clear, allow only leters, numbers and slashes
	if(!empty($raw_route) and preg_match('/^[\p{L}\/\d]++$/uD', $_SERVER["PATH_INFO"]) == 0){
		die("Invalid URL");
	}
 
	//extract parameters
	$url_pieces = explode("/",$_SERVER["PATH_INFO"]);
	$action = $url_pieces[1];
	$params = array();
	if(count($url_pieces)>2){
		$params = array_slice($url_pieces, 2);
	}	
 
	//when no action is passed default action is performed
	if(empty($action)){
		$action="default";
	}
 
	//make sure the route is defined
	if(!in_array( $action, array_keys($routes))){
		die("Nothing to see here");
	}
 
	//all checked, execute requested funcion with provided parameters
	$action_function = $routes[$action];
	$action_function($params);
 
}
 
//just an example
function sayhello(){
	echo "Hello to you too!";
}
 
//another example
function computesum(){
	$params = func_get_arg(0);
 
	$sum = 0;
	$i=0;
	foreach($params as $par){
		$par = intval($par);
		$sum += $par;
		if ($i !=0){echo " + ".$par;}
		else{echo $par;}
		$i++;
	}
 
	echo " = " . $sum;
}
 
//run the whole thing
dispatch();