Apéro fonctionnel 

Bob 

Bob public class Human { private String name; public Human(String name) { this.name = name; } public String getName() { return name; } } Human bob = new Human("Bob"); bob.getName(); 

Container 

public class Container { private T value; public T getValue() { return this.value; } public Container(T value) { this.value = value; } } Container 

Container | exemple Container bottle = new Container(""); bottle.getValue(); // Container bob = new Container(”Bob"); bob.getValue(); // Bob 

Functor 

Functor public class Functor extends Container { public Functor(T value) { super(value); } public Functor map(Function f) { return new Functor(f.apply((T) this.getValue())); } } 

Functor in action Functor bouteilleMagique = new Functor(""); Functor autreBouteille = bouteilleMagique .map(contenu -> contenu + "") // plus de poire .map(contenu -> contenu + ""); // plus de poire System.out.println( autreBouteille.getValue() // ); 

.map(ajouterPoire) .map(ajouterPoire) .getValue() 

Functor dans la vraie vie 

Functor in action bis Functor content = new Functor("Hello World") Functor html = content .map(value -> "

" + value + "

") .map(value -> "" + value + "") .map(value -> "" + value + ""); System.out.println(html.getValue());

Hello World



Functor(Functor(Functor(…))) 

Functor | … dans un functor, dans un … Function> ajouterPoire = contenu -> new Functor(contenu + ""); bouteilleMagique .map(contenu -> new Functor(contenu + "")) .getValue() // Functor@3e3abc88 Type attendu: Functor> Puis: Functor>> etc... 

.map(ajouterPoire) .map(ajouterPoire) 

Du coup la Monad Identity 

Monad public class Monad extends Container { public Monad(T value) { super(value); } public Monad map(Function f) { return new Monad(f.apply((T) this.getValue())); } public Monad flatMap(Function> f) { return f.apply((T) this.getValue()); } } 

Monad | sample Monad bouteilleMagique = new Monad(""); System.out.println( autreBouteille .flatMap(contenu -> new Monad(contenu + " ")) .flatMap(contenu -> new Monad(contenu + " ")) .getValue() ); // 

.flatMap(ajouterPoire) .flatMap(ajouterPoire) .getValue() 

Monade utile Identity 

Monad Identity in RL Monad prixDeDepart = new Monad(10000.0); // options Function optionClim = prix -> prix + 2000.0 ; Function interieurCuir = prix -> prix + 5000.0 ; Function vitresTeintees = prix -> prix + 3000.0 ; Monad prixVoitureToutesOptions = prixDeDepart .map(optionClim) .map(interieurCuir) .map(vitresTeintees); System.out.println(prixVoitureToutesOptions.getValue()); // 20 000 

Vous utilisez déjà des Monad(e)s 

un stream a une map et une flatMap! Stream c’est une api qui utilise les lambdas et qui permet de faire des choses sympas avec les collections 

.map() 

TinyToon class TinyToon { public String pseudo; public String avatar; public TinyToon(String pseudo, String avatar) { this.pseudo = pseudo; this.avatar = avatar; } } 

List tinyToons = Arrays.asList( new TinyToon("Bob", ""), new TinyToon("Jane", ""), new TinyToon("Sam", ""), new TinyToon("John", "") ); List myList = tinyToons .stream() .map(toon -> toon.pseudo + toon.avatar) .collect(Collectors.toList()); System.out.println(myList); // [“Bob“, “Jane“, “Sam“, “John“] 

.flatMap() 

class TinyToon { public String pseudo; public String avatar; public List buddies; public TinyToon(String pseudo, String avatar) { this.pseudo = pseudo; this.avatar = avatar; } public TinyToon(String pseudo, String avatar, List buddies) { this.pseudo = pseudo; this.avatar = avatar; this.buddies = buddies; } } 

List tinyToons = Arrays.asList( new TinyToon("Bob", "", Arrays.asList( new TinyToon("Ted", ""), new TinyToon("Polo", ""))), new TinyToon("Jane", "", Arrays.asList( new TinyToon("Zed", ""), new TinyToon("Grou", ""))), new TinyToon("Sam", "", Arrays.asList( new TinyToon("Kate", ""), new TinyToon("Nike", ""))), new TinyToon("John", "", Arrays.asList( new TinyToon("Ray", ""), new TinyToon("Zoe", ""))) ); [ [, ], [, ], [, ], [, ] ] 

Je veux les avatars des buddies tinyToons.stream() .flatMap(toon -> toon.buddies.stream()) .map(toon -> toon.avatar) .collect(Collectors.toList()) [ [, ], [, ], [, ], [, ] ] [“”, ””, ””, ””, ””, ””, ””, ””] 

une autre super Monad(e) en Java 8: Optional Qui va nous servir à traiter les NPE 

Le problème: c’est Null Ça ne veut pas dire grand chose Ce n’est pas vraiment un type Et poutrtant, out type en Java peut être null 

Optional permet de modéliser null Optional a 2 sous types / sous états Optional.of() Optional.empty() // pas de 

Optional.of( ) Optional.empty() 

Mais repartons sur les toons … 

TinyToon class TinyToon { public String pseudo; public String avatar; public TinyToon(String pseudo, String avatar) { this.pseudo = pseudo; this.avatar = avatar; } } 

NPE before Function getToon = key -> { Map tinyToons = new HashMap() {{ put(1, new TinyToon("Bob", "")); put(2, new TinyToon("Jane", "")); put(3, new TinyToon("Sam", "")); put(4, new TinyToon("John", "")); }}; return tinyToons.get(key); }; System.out.println(getToon.apply(2).avatar); System.out.println(getToon.apply(4).avatar); System.out.println(getToon.apply(6).avatar); //⚠ le toon 6 n’existe pas > > > Exception in thread "main" java.lang.NullPointerException at SearchToons.main(SearchToons.java:20) 

NPE after (Java 8) Function> getMayBeToon = key -> { Map tinyToons = new HashMap() {{ put(1, new TinyToon("Bob", "")); put(2, new TinyToon("Jane", "")); put(3, new TinyToon("Sam", "")); put(4, new TinyToon("John", "")); }}; return Optional.ofNullable(tinyToons.get(key)); }; 

NPE after (Java 8) getMayBeToon.apply(6) getMayBeToon.apply(3) Optional.empty Optional[TinyToon@3e3abc88] getMayBeToon.apply(6).map(toon -> toon.avatar) getMayBeToon.apply(3).map(toon -> toon.avatar) Optional.empty Optional[] getMayBeToon.apply(6).map(toon -> toon.avatar).orElse("") // getMayBeToon.apply(3).map(toon -> toon.avatar).orElse("") // 

Optional + flatMap class LittleToon { public Optional pseudo; public Optional avatar; public LittleToon(String pseudo, String avatar) { this.pseudo = Optional.ofNullable(pseudo); this.avatar = Optional.ofNullable(avatar); } } 

Optional + flatMap Function> getMayBeToon = key -> { Map littleToons = new HashMap() {{ put(1, new LittleToon("Bob", "")); put(2, new LittleToon("Jane", "")); put(3, new LittleToon("Sam", "")); put(4, new LittleToon("John", "")); }}; return Optional.ofNullable(littleToons.get(key)); }; 

Optional + flatMap getMayBeToon.apply(3).map(toon -> toon.avatar); Optional[Optional[]] getMayBeToon.apply(3).flatMap(toon -> toon.avatar); Optional[] 

Either, another ❤ monad there is no Either with Java 8 A type with 2 sub-types 

Either.right(pear) Either.left(bad pear) https://gist.github.com/k33g/011b1f22904c04462a98162c1a27c594 Either.isLeft() Either.isRight() 

Catamorphisme toInt.apply("40").map(value -> value + 2) .cata(err -> { System.out.println(" ouille"); return 0; }, res -> { // right System.out.println(" yes: " + res); return res; }); // yes: 42 

Catamorphisme toInt.apply("quarante-deux").map(value -> value + 2) .cata(err -> { System.out.println(" ouille"); return 0; }, res -> {// right System.out.println(" yes: " + res); return res; }); // ouille