Why won't my AJAX script work?

Why won't this AJAX script work?


Javascript part:

//get xmlhttp
xmlhttp = null;
if (window.XMLHttpRequest)
{
// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp = new XMLHttpRequest();
}
else
{
// code for IE6, IE5
  xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}

//print
function print()
{
	if (xmlhttp.readyState == 4)
	{
		document.getElementById('textbox').innerHTML = xmlhttp.responseText;
	}
}

//on submit
function submit()
{
	xmlhttp.open('POST','function.php',true);
	var text = document.getElementById('textbox').value;
	var param = text;
	xmlhttp.send(param);
	xmlhttp.onreadystatechange = print();
}

Code (markup):

PHP code:

<?PHP
$var = $_POST['param'];
echo $var;
?>

Code (markup):

 

[QUOTE]xmlhttp.onreadystatechange = print();[/QUOTE]

Code (markup):

xmlhttp.onreadystatechange = print;

Code (markup):

Except don't call it print because that's already a property of window.