reevik

val list = List(1,2,3,4,5)
list.map(e => List(e - 1, e, e + 1))

> res0: List[List[Int]] = List(List(0, 1, 2), List(1, 2, 3), List(2, 3, 4), List(3, 4, 5), List(4, 5, 6))

reevik

val list = List(1,2,3,4,5) 
list.flatMap(e => List(e - 1, e, e + 1))  

> res0: List[Int] = List(0, 1, 2, 1, 2, 3, 2, 3, 4, 3, 4, 5, 4, 5, 6)

reevik

trait M[T] {  def flatMap[U](f: T => M[U]): M[U] }

reevik

Cat cat = catService.getCat(); // a real cat created which meows
catbar.enter(cat); 
Cat lion = catService.getCat(); // this time the service gives you a lion instance back.
catbar.enter(lion);
catbar.singTogether(); // party begins: meoww moewww ROOARRR meow

reevik

Lion lion = new Lion(AnimalSoundLib.ROAR);
lion.sing(); // roarrr

reevik

public class CatBar {
    private List<Cat> catFriends = new ArrayList<>();
    public void enter(Cat cat) {
        catFriends.add(cat);
    }
    public void singTogether() {
        for (Cat cat: catFriends) {
            cat.sing();
        }
    }

reevik

public class Lion extends Cat {
    public Lion(AnimalSound animalSound) {
        super(animalSound);
    }
    public void hunt() {}
    // and other lion related methods.
}

reevik

Cat cat1 = new Cat(AnimalSoundLib.MEOW);
cat1.sing(); // meooww
Cat cat2 = new Cat(AnimalSoundLib.MEOOO);
cat2.sing(); // meoooo
// more cats

reevik

public class Cat {
    private AnimalSound sound;
   
    public Cat(AnimalSound animalSound) {
        this.sound = animalSound;
    }
    public void sing() {
        soundEffect(sound);
    }
}

reevik

;; Multimethod definition showing that the run 
;; might have multiple informations. The identity
;; function is used as dispatcher function to 
;; determine which implementation of run is to be
;; called
(defmulti run identity)
;; The run method implementation for temp. 
(defmethod run "temp"
    [city day] 
    (get-temp city day))