Lacking the magic of solutions by LanX or choroba, this solution uses Algorithm::Combinatorics and List::MoreUtils. 
#!/usr/bin/perl
use strict;
use warnings;
use Algorithm::Combinatorics 'variations_with_repetition';
use List::MoreUtils 'pairwise';

my @a = 1 .. 3;
my @b = qw/a b/;

my @c;

my $iter = variations_with_repetition (\@b, scalar @a);

while (my $tuple = $iter->next) {
    no warnings 'once'; # silence warnings about $a $b only used once
    my @temp = pairwise { [$a,$b] } @a, @$tuple;
    push @c, \@temp;
}

use Data::Dump; dd \@c;

[download]
Dump output: 
[
  [[1, "a"], [2, "a"], [3, "a"]],
  [[1, "a"], [2, "a"], [3, "b"]],
  [[1, "a"], [2, "b"], [3, "a"]],
  [[1, "a"], [2, "b"], [3, "b"]],
  [[1, "b"], [2, "a"], [3, "a"]],
  [[1, "b"], [2, "a"], [3, "b"]],
  [[1, "b"], [2, "b"], [3, "a"]],
  [[1, "b"], [2, "b"], [3, "b"]],
]

[download]

In reply to Re: combinations of multiple variables which can assume multiple values by Cristoforo
in thread combinations of multiple variables which can assume multiple values by jgraeve

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