phpyh-fp.github.io/index.html at main · klimick/phpyh-fp.github.io · GitHub

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<!DOCTYPE html>
<html lang="en">
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<body>
    <div class="reveal">
        <div class="slides"><section  data-markdown><script type="text/template"><!-- .slide: class="drop" data-background-image="./title.jpg" template="" -->
<div class="" style="position: absolute; left: 0px; top: 0px; height: 900px; width: 960px; min-height: 900px; display: flex; flex-direction: column; align-items: center; justify-content: center" absolute="true">


</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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### Что такое функциональное программирование?

<img src="what-is-fp-question.jpg" alt="" style="width: 960×540px; object-fit: fill">
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
<div class="" style="position: absolute; left: 0px; top: 0px; height: 900px; width: 960px; min-height: 900px; display: flex; flex-direction: column; align-items: center; justify-content: center" absolute="true">

Функциональное программирование — это набор выражений, который нужно каким-то образом интерпретировать
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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### Установки функциональных языков

- Ссылочная прозрачность
- Неизменяемые данные
- Expressions вместо statements
- Данные и функции отдельно
- Композиция
- Контроль эффектов
- Статическая типизация
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### Ссылочная прозрачность

Замена одного выражения другим без какого-либо изменения результата
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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#### Императивная программа

```php [|1,5,9|3,7,10|2,6,14]
function lhs(): int {
  log('lhs() call');
  return 1;
}
function rhs(): int {
  log('rhs() call');
  return 41;
}
function app(): int {
  return lhs() + rhs();
}

$result = app();
log($result);
```

```txt
[log]: lhs() call
[log]: rhs() call
[log]: 42
```
<!-- .element: class="fragment" -->
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#### Подстановка результата операций может менять смысл

```php
function app(): int {
	return 1 + 41;
}

log(app())
```


```txt
[log]: calculate
[log]: 42
```
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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Результат функции с побочными эффектами невозможно инлайнить
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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#### Ссылочно прозрачная альтернатива

```php [|2,5|9|10|11]
function lhs(): Expr<int> {
    return Expr::log('call lhs()')->map(fn() => 1);
}
function rhs(): Expr<int> {
    return Expr::log('call rhs()')->map(fn() => 41);
}

function app(): Expr<int> {
    return Exp::scope()
	  ->bind(a: lhs(), b: rhs())
	  ->map(fn($i) => $i->a + $i->b);
}
```
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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#### Запуск программы (на краю света)

```php []
unsafeRun(
	expr: app()->flatMap(Expr::log(...)),
	interpreter: new ExprInterpreter(),
);
```
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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#### Возможность инлайнить результат функции

```php []
$app = Expr::scope()
	->bind(
		a: Expr::log('call lhs()')->map(fn() => 1),
		b: Expr::log('call rhs()')->map(fn() => 41),
	)
	->map(fn($i) => $i->a + $i->b)
	->flatMap(Expr::log(...))

unsafeRun($app, new ExprInterpreter());
```
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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### Неизменяемые данные

Все данные заморожены 🥶

Они никогда не будут изменены!
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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В PHP это не по умолчанию

*И без гарантий на неизменяемость...*
<!-- .element: class="fragment" -->
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#### Однажды создан и не может быть изменен ✅

```php
final readonly class Person
{
	public function __construct(
		public int $id,
		public string $name,
	) {}
}
```
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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#### Изменяемый класс❗️
```php
final class Address
{
	public function __construct(
		public string $street,
	) {}
}
```
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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#### Могут быть ссылки на изменяемые объекты

```php [6]
final readonly class Person
{
	public function __construct(
		public int $id,
		public string $name,
		public Address $address,
	) {}
}
```
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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С readonly в PHP есть более неприятный момент

*Это копирование readonly объектов...*
<!-- .element: class="fragment" -->
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#### Это не будет работать ❌

```php
final readonly class Person
{
	public function __construct(
		public int $id,
		public string $name,
	) {}
}

$a = new Person(id: 42, name: 'test');
$b = clone $a;
$b->name = 'NewName';
// Error: Cannot modify readonly property Person::$name
```
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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#### "Рабочий" вариант на текущий момент

```php [|10]
final readonly class Person
{
	public function __construct(
		public int $id,
		public string $name,
	) {}
}

$a = new Person(id: 42, name: 'test');
$b = new Person(id: $a->id, name: 'newName');
```

*Копируем все свойства вручную...*
<!-- .element: class="fragment" -->
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Есть пару rfc которые могут это исправить

https://wiki.php.net/rfc/clone_with
https://wiki.php.net/rfc/records
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#### Пустяки на бесконечном пути бытия

<img src="immutable-ds.gif" alt="" style="object-fit: scale-down">
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#### Отсутвие незменяемых структур данных

- Нет в PHP core
- Нет библиотек
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#### Простой неизменяемый список

```scala 3 []
enum Lst[+A]:
  case Cons(head: A, tail: Lst[A]) extends Lst[A]
  case Nil extends Lst[Nothing]
```
</div></script></section><section  data-markdown><script type="text/template"><!-- .slide: class="drop" template="" -->
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#### Все версии списка доступны

```scala 3
val v1 = Lst.Cons(1, Lst.Nil) // [1]
val v2 = Lst.Cons(2, v1)      // [1, 2]
val v3 = Lst.Cons(3, v2)      // [1, 2, 3]
val v4 = Lst.Cons(4, v3)      // [1, 2, 3, 4]
val v5 = Lst.Cons(5, v4)      // [1, 2, 3, 4, 5]
val v6 = Lst.Cons(6, v5)      // [1, 2, 3, 4, 5, 6]
```
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#### Давайте сделаем это на php

[Вот в javascript есть](https://github.com/immutable-js/immutable-js)
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PHP погибает с segfult при глубогой вложенности объектов 🤡

<img src="lol-segfault.gif" alt="" style="width: 640px; height: 420px; object-fit: fill">


https://github.com/php/doc-en/issues/1228
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### Циклы и ветвления забанены

<img src="no-more-statements.jpg" alt="" style="object-fit: scale-down">
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#### Старые друзья VS новые

- for/while/continue/break - рекурсия
- if/else/switch - pattern matching
- return - просто не нужен
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#### Ну как там с рекурсией?

<img src="recursion-question.jpeg" alt="" style="width: 640px; height: 420px; object-fit: fill">
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```php [|2-3|4]
function sum(list<int> $nums): int {
    return $nums === []
        ? 0
        : $nums[0] + sum(array_slice($nums, offset: 1));
}
```
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#### Причины из-за которых рекурсия это больно

- Stack-frame на каждый рекурсивный вызов
- Жалобы xdebug на большую вложенность
- Segfault (если вам очень сильно повезет)
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#### Хвостовая рекурсия

Частный случай рекурсии, при котором рекурсивный вызов является последней операцией перед возвратом из функции

*Оптимизируется в цикл*
<!-- .element: class="fragment" -->

*Не реализованно в PHP*
<!-- .element: class="fragment" -->
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#### Пример хвостовой рекурсии

```scala 3 [|1|3|4-5|6|2|8]
def sum(nums: List[Int]): Int =
  @tailrec
  def loop(nums: List[Int], acc: Int = 0): Int =
    if nums.isEmpty
    then acc
    else loop(nums.tail, acc + nums.head)

  loop(nums)
```
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#### Свертка

Если у вас получается сделать хвостовую рекурсию, то получится сделать свертку

```php [|3|4|6]
function sum(list<int> $nums): int
{
	$initial = 0;
	$reducer = fn (int $sum, int $num) => $sum + $num;

    return array_reduce($nums, $reducer, $initial);
}
```
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#### Взаимная рекурсия

```php []
function even(int $i): bool
{
    return $i === 0
	    ? true
	    : odd($i - 1);
}

function odd(int $i): bool
{
    return $i === 0
	    ? false
	    : even($i - 1);
}

var_dump(even(1)); // false
var_dump(even(2)); // true
var_dump(even(666_666_666)); // Out of memory
```
https://3v4l.org/lCOerV#v8.3.13
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#### Trampoline

Если не удается сделать хвостовую рекурсию

```php
function evenT(int $i): Trampoline<bool> {
    return $i === 0
        ? new Done(true)
        : new Cont(fn() => oddT($i - 1));
}

function oddT(int $i): Trampoline<bool> {
    return $i === 0
        ? new Done(false)
        : new Cont(fn() => evenT($i - 1));
}

var_dump(runTrampoline(evenT(1))); // false
var_dump(runTrampoline(evenT(2))); // true
var_dump(runTrampoline(evenT(666_666_666))); // true
```

https://3v4l.org/aev4d#v8.3.13
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#### Pattern matching for poor PHP programmers

```php [|3|4|5-8]
function loop(list<int> $nums, int $acc = 0): int
{
    return match (true) {
        $nums === [] => $acc,
        $nums !== [] => loop(
	        nums: array_slice($nums, offset: 1),
	        acc: $acc + $nums[0],
		),
    };
}
```
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Как выглядит богатый pattern matching

```scala 3 [|4|5|6]
def sum(nums: List[Int]): BigInt =
  @tailrec
  def loop(nums: List[Int], acc: Int = 0): int =
	nums match {
	  case Nil => acc
	  case head :: tail => loop(tail, acc + head)
	}

  loop(nums)

```
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#### Ожидаем похожее в PHP

<img src="wait-for-patmat.gif" alt="" style="object-fit: scale-down">


https://wiki.php.net/rfc/pattern-matching
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### Функции как значения

- Передавать функции в другие функции
- Возвращать функции из функций
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#### Было всегда (или почти)

```php []
$intToString = function (int $a) {
    return (string) $a;
};
```
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#### Появилось с PHP 7.4

```php []
$intToString = fn (int $a) => (string) $a;
```
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#### Появилось аж с PHP 8.1

```php
function intToString(int $a): string
{
    return (string) $a;
}

$intToString = intToString(...);
```
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Все текущие стат анализаторы лагают в области анонимных функций 🥲

<img src="sa-sucks.jpg" alt="" style="object-fit: scale-down">
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#### Что может быть проще ?

```php []
function identity<A>(A $value): A
{
	return $value;
}
```
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#### Чуть сложнее, но все еще просто

```php []
function simple((int => int) $intToInt): int
{
	return $intToInt(42);
}
```
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#### "Слишком сложно"

```php [|1-2|4-5|7-8]
// PHPStan выводит тип Closure<A>(A): A
$id = identity(...);

// Но не может понять, что $fn можно передать сюда
simple($id);

// А так можно 🤡
simple(fn($i) => $i);
```

https://phpstan.org/r/0a262bfb-ade5-4303-b03a-ac0521634b5e
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### Композиция функций

Если функции являются значениями, то эти значения можно комбинировать друг с другом
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#### Комбинировать их можно в двух стилях

- Data-first
- Data-last
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#### Только унарные функции

<img src="only-unary-functions.gif" alt="" style="width: 640px; height: 420px; object-fit: fill">
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#### Data first
- Передаем изначальные данные
- Вычисляем слева направо

```php [|6|7|8]
$addOne = fn(int $a) => $a + 1;
$intToString = fn(int $a) => (string) $a;

// "42"
$result = pipe(
	41,
	$addOne,
	$intToString
);
```
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#### Data last
- Передаем функции для выполнения слева направо
- Результатом будет композиция функций

```php [|5|8]
$addOne = fn(int $a) => $a + 1;
$intToString = fn(int $a) => (string) $a;

// Closure(int): string
$addOneAndIntToString = compose($addOne, $intToString);

// "42"
$result = $addOneAndIntToString(41);
```
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#### Невозможно объявить именованую функцию

```php []
// Так не можем:
const addOneAndToString1 = compose(
	addOne(...),
	intToString(...),
);

// И так не можем:
function addOneAndToString2 = compose(
	addOne(...),
	intToString(...),
);
```
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#### Можем ли мы сделать такие функции в PHP?

- С точки зрения php - да ✅
- C точки зрения стат анализа - нет 🥲
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#### Элементарная функция с невыразимой сигнатурой

```php
/**
 * Что здесь написать ? 🗿🗿🗿
 */
function pipe(mixed $value, callable ...$transformations)
{
    $result = $value;

    foreach ($transformations as $transformation) {
	    $result = $transformation($result);
	}

    return $result;
}
```

*Тоже касается и функции compose...*
<!-- .element: class="fragment" -->
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Хотели добавить pipe operator в PHP

https://wiki.php.net/rfc/pipe-operator-v2

Но слишком много голосов было против 🥲

Ждем pipe-operator-v3?
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#### Проверки на null мешают композиции

<img src="iferrneqerr.webp" alt="" style="object-fit: scale-down">
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```php [|1|3-4|5-9]
$num = getNullableInt();

return $num === null
  ? null
  : pipe(
      $num,
      addOne(...),
      intToString(...),
    );
```
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```php []
return pipe(
  getNullableInt(),
  addOne(...),
  intToString(...),
);
```
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#### Украдем `Option[A]` к себе в `PHP`

```scala 3 [|2|3|5-6|8-9]
enum Option[+A]:
  case Some(value: A) extends Option[A]
  case None extends Option[Nothing]

// Значение определено
val fortyTwo = Option.Some(42)

// Значение неопределено
val none = Option.None
```
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#### Украли, но все не получилось

```php [|1-2|4-11|13-14]
/** @template-covariant A */
interface Option {}

/**
 * @template-covariant A
 * @implements Option<A>
 */
final readonly class Some implements Option {
    /** @param A $some */
    public function __construct(public mixed $some) {}
}

/** @implements Option<never> */
enum None implements Option { case instance; }
```
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#### Сможем украсть полностью после этого `RFC`

https://wiki.php.net/rfc/tagged_unions


*Добаввить мем про кражу уровень 100*
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Функции которые будут возвращать `Option<A>` легко композировать
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`Option<int>`
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`(int -> string)`
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`(Option<int> -> Option<string>)`
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#### Та самая функция

```php [|7|9|10|11|12]
/**
 * @template A
 * @template B
 * @param callable(A): B $ab
 * @return callable(Option<A>): Option<B>
 */
function map(callable $ab): callable
{
    return static fn (Option $fa) =>
	    isSome($fa)
			? new Some($ab($fa->some))
			: None::instance;
}
```
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#### Попробуем

```php [|1-2|5-9|6|7|8|]
/** @var Option<int> */
$num = getOptionInt();

// Option<string>
$result = pipe(
    $num,
    Option\map(addOne(...)),
    Option\map(intToString(...)),
);
```
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`Option<string>`
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`(string -> Option<int>)`
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`(Option<string> -> Option<int>)`
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#### Та самая функция

```php [|7|9|10|11]
/**
 * @template A
 * @template B
 * @param callable(A): Option<B> $ab
 * @return callable(Option<A>): Option<B>
 */
function flatMap(callable $ab): callable
{
    return static fn (Option $fa) =>
	    isSome($fa)
			? $ab($fa->some)
			: None::instance;
}
```
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#### Какой-то command handler

```php [|8|9|4,10]
final readonly class CreateProjectInviteHandler
{
    /**
     * @return Option<ProjectInvite>
     */
    #[Handler]
    public function __invoke(
	    CreateProjectInvite $command,
	    MessageBus $bus,
	): Option {...}
}
```
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```php [|1|3-4|7|9-11|13]
$user = $bus(new FindUser($command->userId));

if ($user === null) {
    return null;
}

$project = $bus(new FindProject($command->projectId));

if ($project === null) {
    return null;
}

return new ProjectInvite($user, $project);
```
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Найдем `Project` затем `User` и создадим `ProjectInvite`

```php [|2|3|4|5|5-8]
return pipe(
	$bus(new FindUser($command->userId)),
    Option\flatMap(fn($user) => pipe(
        $bus(new FindProject($command->projectId)),
        Option\map(fn($project) => new ProjectInvite(
		    user: $user,
		    project: $project,
	    )),
    )),
);
```
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`Project` зависит от `User`

Из-за этого появляется вложенность.
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Нам нужна do-notation
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Как выглядит do-notation в Scala

```scala 3 [|3-6|4|5|6]
final class CreateProjectInviteHandler:
  def handle(msg: CreateProjectInvite, bus: MessageBus) =
    for
      user <- bus(GetUser(msg.userId))
      project <- bus(GetProject(msg.projectId))
    yield ProjectInvite(user, project)
```
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Все это syntax-sugar для такой конструкции

```scala 3
bus(GetUser(msg.userId))
  .flatMap(user =>
    bus(GetProject(message.projectId))
      .map(project =>
        ProjectInvite(user, project)
      )
  )
```
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