Simple DSL for building up a Person

Person.DSL.cs

public static class PersonFactory
    {
        public static FirstNameExpression CreatePerson()
        {
            return new FirstNameExpression(new Person());
        }
    }

    public class FirstNameExpression
    {
        private Person _person;
        public FirstNameExpression(Person person)
        {
            _person = person;
        }

        public MiddleNameExpression WithFirstName(string first)
        {
            _person.FirstName = first;
            return new MiddleNameExpression(_person);
        }
    }

    public class MiddleNameExpression
    {
        private Person _person;
        public MiddleNameExpression(Person person)
        {
            _person = person;
        }

        public LastNameExpression WithMiddleName(string middle)
        {
            _person.MiddleName = middle;
            return new LastNameExpression(_person);
        }
    }

    public class LastNameExpression
    {
        private Person _person;
        public LastNameExpression(Person person)
        {
            _person = person;
        }

        public Person WithLastName(string last)
        {
            _person.LastName = last;
            return _person;
        }
    }