I have a small PHP script (below) that works on a standard .php page, but I'm having some trouble getting it to work in Silverstripe

<?php 
function ChangeCurrency($from, $to, $amount)
{
   $content = file_get_contents('https://www.google.com/finance/converter?a='.$amount.'&from='.$from.'&to='.$to);

   $doc = new DOMDocument;
   @$doc->loadHTML($content);
   $xpath = new DOMXpath($doc);
   $result = $xpath->query('//*[@id="currency_converter_result"]/span')->item(0)->nodeValue;
   return str_replace(' '.$to, '', $result);
}
echo ChangeCurrency('EUR', 'GBP', 100); // returns 0.7216
 ?>

There's nothing wrong with the above code, but as I can't put this directly into my template I tried adding it as a function in code/ProductPage.php

class ProductPage_Controller extends Page_Controller {
	
	public function ChangeCurrency($from, $to, $amount) {
	  $content = file_get_contents('https://www.google.com/finance/converter?a='.$amount.'&from='.$from.'&to='.$to);
	
	  $doc = new DOMDocument;
	  @$doc->loadHTML($content);
	  $xpath = new DOMXpath($doc);
	  $result = $xpath->query('//*[@id="currency_converter_result"]/span')->item(0)->nodeValue;
	
	return str_replace(' '.$to, '', $result);
	}

}

Then on the template ProductPage.ss I tried

<% control ChangeCurrency('EUR', 'GBP', 100) %> $ChangeCurrency<% end_control %>

(It's an older site on Silverstripe 2.4.5 hence 'control' instead of 'with')

What am I doing wrong here?

To answer my own question:

I changed the function to include the price and all the variables (as I'll always be converting from EUR to GBP)

public function ChangeCurrency() {
	$content = file_get_contents('https://www.google.com/finance/converter?a='.$this->Price.'&from=EUR&to=GBP');
	
	$doc = new DOMDocument;
	@$doc->loadHTML($content);
	$xpath = new DOMXpath($doc);
	$result = $xpath->query('//*[@id="currency_converter_result"]/span')->item(0)->nodeValue;
	
	return str_replace('GBP', '', $result);
	}

Then on the template I just need to put $ChangeCurrency

ps. I updated the title of this post to include 'Currency Convertor' as this is a very handy currency conversion script for Silverstripe if anyone is looking for one