#!/usr/bin/env perl

use strict;
use warnings;

# Functional (naïve)
sub iter1 {
    my ($fibs, $acc) = @_;
    my ($a, $b) = @$fibs;
    if ($a > 4_000_000) {
        return $acc;
    } else {
        iter1([$b, $a+$b], $a & 1 ? $acc : $acc + $a);
    }
}
print iter1([1, 2], 0), "\n";

# Functional (tail recursive)
sub iter2 {
    my ($fibs, $acc) = @_;
    my ($a, $b) = @$fibs;
    if ($a > 4_000_000) {
        return $acc;
    } else {
        @_ = ([$b, $a+$b], $a & 1 ? $acc : $acc + $a);
        goto &iter2;
    }
}
print iter2([1, 2], 0), "\n";

# Imperative
my ($a, $b) = (1, 2);
my $resp = 0;
do {
    $resp += $a unless ($a & 1);
    ($a, $b) = ($b, $a+$b);
} while ($a <= 4_000_000);

print "$resp\n"