Hardly original but my own fibonacci number generator.

use strict;
use warnings;
$| = 1;

sub infinite_fib {
    my ($last,$curr) = @_;
    return sub {       
       my $temp = $last + $curr;
       $last = $curr;
       $curr = $temp;
       return $curr;
   };
}
my $next_fib = infinite_fib( 1,0 );
print $next_fib->(), "\n" for(1..10);
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Kinda fun just because it reaches infinity in a pretty big hurry if you let it run.