sub seq_reset {
        my $seq = shift;
        if ($seq) { 
            1 while $seq->();
        }
        $seq;
    }

    sub seq_zip {
        my $seqs = seq( @_ ); # seq of seqs (!)
        my $seq_count = @_;
        seqsub {
            my @outvals;
            while (my $seq = $seqs->()) {
                if (my @val = $seq->()) {
                    push @outvals, @val;
                }
                else {
                    seq_reset( $seqs->() ) for 1 .. $seq_count;
                    seq_reset( $seqs );
                    return ();
                }
            }
            return @outvals;
        }
    }