RTF Template: BI Publisher: I want to use the if condition with the to_number() function

RTF Template: BI Publisher: I want to use the if condition with the to_number() function. In my case the value is in string format, first I want to convert that string to a number and then compare that number with zero.

something like this - 

<?xdofx:if(xdofx:to_number(AMOUNT))>0 ?>

but the above is not working.