public function addMember(Request $req, MemberRepository $repo)
 {
     $id = MemberId::generate();
     $member = Member::instantiate($id, $req->input('first_name'), $req->input('last_name'));
     $repo->save($member);
     return redirect('/admin/member');
 }
 public static function instantiate(MemberId $id, $first_name, $last_name)
 {
     $member = new Member();
     $member->apply(new MemberJoinedFrancken($id, $first_name, $last_name));
     return $member;
 }