sub make_iter_deeper {
    my @AoA = @_;
    my @idx;
    my $i = 0;     # keeping it simple
    $idx[0] = -1;  # same as $idx = -1 above;
    my @return;

    return sub {

        # if the index of the array i'm working in is
        # past the end of elements
        if ( ++$idx[$i] > $#{@{$AoA[$i]}} ) {
            return;
        }
        # if not, put the next element in the return value
        else {
            $return[$i] = $AoA[$i][$idx[$i]]
        }
        return @return;
    }
}

my $iter = make_iter_deeper([3,4,6,7]);
print join(',',@_) . "\n" while( @_ = $iter->() );