fakename

// Loading both firstnames and lastnames concurrently.

fn, ln, err := func() (Nameset, Nameset, error) {
	dst := make(chan Nameset, 2)

	{
		var eg errgroup.Group
		for _, _s := range []struct {
			src   string
			label string
		}{
			{
				src:   "data/noms_sorted_by_count.csv",
				label: "lastnames",
			},
			{
				src:   "data/prenoms_sorted_by_count.csv",
				label: "firstnames",
			},
		} {
			s := _s
			eg.Go(func() error {
				f, err := os.Open(s.src)
				if err != nil {
					return fmt.Errorf("%s: os: open: %w", s.label, err)
				}
				ns, err := NewSet(f, NamesetWithRand(rand.New(rand.NewSource(42)))) // read also go doc math/rand
				if err != nil {
					return fmt.Errorf("%s: new set: %w", s.label, err)
				}
				dst <- ns
				return nil
			})
		}

		if err := eg.Wait(); err != nil {
			return nil, nil, err
		}

	}

	{

		var fn, ln Nameset

		ns := <-dst
		if ns.Label() == "lastnames" {
			ln = ns
			fn = <-dst
		} else {
			fn = ns
			ln = <-dst
		}

		return fn, ln, nil

	}

}()

if err != nil {
	fmt.Println(err)
	return
}

fmt.Println(fn.RandomName(), ln.RandomName())

Output:

MARCELLE LEMEE