Thanks for the tutorial! But I think you have an error in the fib function! If you really start with my $last = 0; and your fib function, you'll get this error, as you've produced a never ending recursion: Deep recursion on subroutine "IkiWiki::Plugin::fib::fib" at ./fib.pm line 29. So the fib function should better look like this, which is its true definition (see [[Wikipedia|http://de.wikipedia.org/wiki/Fibonacci-Folge]], for example): sub fib { my $num=shift; return 0 if $num == 0; return 1 if $num == 1; return fib($num - 1) + fib($num - 2); } Just as a hint for people who run into this error while doing this tutorial.