#!/usr/bin/perl -w
use strict;

sub fibonacci {
    my ($low, $high) = (1, 0);
    return sub {
        ($low, $high) = ($high, $low + $high);
        return $high;
    };
}
my $iterator = fibonacci();
print $iterator->(), $/ for 1 .. 20;

##</code><code>##

sub fibonacci {
    my $fib = shift;
    return $fib if ! $fib || $fib == 1;
    my ($low, $high) = (1, 0);
    my $iterate = sub {
        ($low, $high) = ($high, $low + $high);
        return $high;
    };
    $iterate->() for 1 .. $fib;
    return $high;
}

print fibonacci(0), $/;

##</code><code>##

#!/usr/bin/perl -w
use strict;

sub fibonacci {
    my $fib = shift;
    return $fib if ! $fib || $fib == 1;    
    my ($low, $high) = (1, 0);
    for (1 .. $fib) {
        ($low, $high) = ($high, $low + $high);
    }
    return $high;
}

print fibonacci(20), $/;