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 ./ line 29.

So the fib function should better look like this, which is its true definition (see Wikipedia, 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.