[Phpwm] Fnuction to calculate a formula

[Colin Taylor]

Hello,
I am on the hunt for a PHP 5 function that will calculate a given formula.
For example:

$formula="2+2";
$result=calculate_formula($formula);
echo "$formula = $result";

Would reult in:

2+2 = 4

Anyone got any ideas?
Cheers,
Colin