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use strict;
use warnings;
use 5.012;
...
while ( my ($f, $s) = $ea->() ) {
    say "First: $f -> second: $s"
}

First: 1 -> second: a
First: 2 -> second: b
First: 3 -> second: c
First: 4 -> second: d
First: 5 -> second: e
First: 6 -> second: f

use strict;
use 5.012;
use List::MoreUtils qw/pairwise/;
...
my @second = qw/a b c d e f/;

pairwise { say "First: $a -> second: $b" } @first, @second;