[thelist] PHP is_nan

[fstorr]

Hi all

This is probably a real newbie error, but PHP's is_nan function is not
playing for me.  I've got this as a test:

<?
$tester = "hello";

if (is_nan($tester))

	{
	echo "this works";
	exit;
	}

else

	{
	echo "don't work";
	exit;
	}
?>

And I get back:

Warning: is_nan() expects parameter 1 to be double, string given in
(address of the page)

Why?!

Regards

Francis