fjDoDemo.java

// given...
class Person {
  final String name;
  final Integer age;
  final Date birth;

  Person(String name, Integer age, Date birth) {
    this.name = name;
    this.age = age;
    this.birth = birth;
  }
}

Maybe<String> getName(String id) {
  return id.equals("toto") ? Just("Toto Titi") : Nothing();
}

Maybe<Integer> getAge(String id) {
  return id.equals("toto") ? Just(36) : Nothing();
}

Maybe<Date> getBirthDate(String name, Integer age) {
  return name.equals("Toto Titi") && age < 40 ? Just(new Date()) : Nothing();
}

// ...we can express

// Monadic Do
Maybe<Person> maybePers = Do
  .$(Maybe.instances, Maybe::narrow

    , () -> getName("toto")

    , __ -> getAge("toto")

    , (name, age) -> getBirthDate(name, age)

    , Person::new);

// Interleaved Dos
 Maybe<Person> maybePers2 = Do
   .$(Maybe.instances, Maybe::narrow
   
     , () -> getName("toto")

     , __ -> getAge("toto")

     , (name, age) -> Do
         .$(Maybe.instances, Maybe::narrow 
           
           , () -> getBirthDate(name, age)
           
           , bd -> new Person(name, age, bd)) // interleaved Dos...

     , (String __, Integer ___, Person p) -> p); // ... need some help

// A test on Eithers created on the fly ; type inference seems to cope with it...
Either<String, Person> personOrError = Do
  .$(Either.instances(), Either::narrow
    
    , () -> getName("toto").toEither(() -> "error getting name")

    , __ -> getAge("toto").toEither(() -> "error getting age")

    , (name, age) -> getBirthDate(name, age).toEither(() -> "error getting birth date")

    , Person::new);

// applicative Do
Maybe<Person> apMaybePers = ApDo.
  $(Maybe.instances, Maybe::narrow
    
    , getName("toto")

    , getAge("toto")

    , Just(new Date())

    , Person::new);

// Traversing on...
List<Maybe<String>> maybes =
  Cons(Just("a"), Cons(Just("b"), Cons(Just("c"), Nil())));

// ... the nice way
Maybe<List<String>> listMaybe1 = List.sequenceMaybe(maybes);

// ... the less nice (but possible, just in case the short cut isn't available) way
Maybe<List<String>> listMaybe2 =
  Maybe.narrow(List.instances.sequence(List::narrow, Maybe.instances, maybes));
    

I've also come up with a poor man's do notation. But I think it still has some security problems. Your input could be valuable.
see: highj/highj#13