use v5.20;
use strict;
use warnings;

use Data::Dump qw( pp );

sub combine 
{
  my ($left, $right) = @_;
  my @out;
  my $reverse = 0;
  for my $el (@$left)
  {
    push @out, map { [ $el, ref $_ ? @$_ : $_ ] } ($reverse ? reverse @$right : @$right);
    $reverse = !$reverse;
  }
  return \@out;
}


pp combine ['A' .. 'F'], combine ['a'..'d'], [1..8];
pp combine [1..3], combine [1..4], [1..3];