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use Algorithm::Loops qw( NestedLoops );

...
   NestedLoops(\@_, sub { push(@rv, [ @_ ]); });
   return \@rv;
}

my $comb = comb([qw(a b c)],[qw(1 2 3)],[qw(- + *)]);

...
));

print(scalar(@$comb), "\n");  # 27

sub comb {
   my @idx = map { 0    } @_;
...
      }
   }
}