use strict;
use warnings;
use feature 'say';
use Algorithm::Combinatorics 'variations_with_repetition';
use List::MoreUtils 'pairwise';
use Data::Dump 'dd';

my @subsets = (
    [ qw/ $ @ % /],
    [ qw/ p q r s /],
    [ qw/ 0 1 /],
);

my $base      = shift @subsets;
my $var_len   = @$base;
my @solutions = [ map [$_], @$base ];

for my $subset ( @subsets ) {
    
    my @variations = variations_with_repetition( $subset, $var_len );

    @solutions = map {
        my $sol = $_;
        map [ pairwise { [ @$a, $b ] } @$sol, @$_ ], @variations
    } @solutions;
}

dd \@solutions;