Getting through the weekend

My upcoming weekend will be filled with a lot of fun and excitement, I have another World Jamboree troop-weekend. Check out this site to see the other people of my troop.

For the people that can not spend a weekend without wondering about PHP I have a little exercise. What is the output of the following piece of code:

<?php 
  function foo($param1, $param2){
    $param1 + $param2;
  }
  
  $result = foo(1,2);

  echo $result;

?> 

Will it be an error, the result of the function or nothing at all? Don't spoil the fun by running it in PHP without thinking about it! The answer was a little surprising for me.