Not an answer to your question, but a solution to your need, maybe...

# arg 0: callback; is passed each generated vector
# arg 1: length of generated vectors
# remaining args: alphabet

sub generate_all_vectors(&$@)
{
    my( $callback, $veclen, @alphabet ) = @_;
    for ( my $i = 0; $i < @alphabet ** $veclen; $i++ )
    {
        my $t = $i; # destructible copy
        $callback->( 
            reverse map
            {
                my $n = $t % @alphabet;
                $t = int( $t / @alphabet );
                $alphabet[$n]
            }
            1 .. $veclen
        )
    }
}

generate_all_vectors { print "@_\n" } 7, 0 .. 9;
[download]