Monads talk examples

1-maybe.php

<?php

abstract class Named {
    public $name;
    public function __construct($name) {
        $this->name = $name;
    }
}

class Country extends Named {
    public $province;
    public function __construct($name, $province = null) {
        parent::__construct($name);
        $this->province = $province;
    }
}

class Province extends Named {
    public $city;
    public function __construct($name, $city = null) {
        parent::__construct($name);
        $this->city = $city;
    }
}

class City extends Named {}

function getCityFromCountry(Country $country) {
    return $country
        ->province
        ->city;
}

$city = new City('Cape Town');
$province = new Province('Western Cape', $city);
$country = new Country('South Africa', $province);

var_dump(getCityFromCountry($country));

2-many.php

<?php

class Genre {
    public function __construct(
        public string $name,
        public array $authors,
    ) {}
}

class Author {
    public function __construct(
        public string $name,
        public array $books,
    ) {}
}

class Book {
    public function __construct(
        public string $name,
        public string $content,
    ) {}
}

function flatMap(array $items, Closure $mapper) {
    return array_merge(
        ...array_map($mapper, $items),
    );
}

function getAllWordsFor(array $genres) {
    return flatMap(
        $genres,
        fn(Genre $genre) => flatMap(
            $genre->authors,
            fn(Author $author) => flatMap(
                $author->books,
                fn(Book $book) => array_map(fn($word) => trim($word), explode(' ', $book->content)),
            ),
        ),
    );

    // return (new Many($genres))
    //     ->then(fn($genre) => $genre->authors)
    //     ->then(fn($author) => $author->books)
    //     ->then(fn($book) => explode(' ', $book->content))
    //     ->value();

    // return (new Many($genres))
    //     ->authors
    //     ->books
    //     ->then(fn($book) => explode(' ', $book->content))
    //     ->value();
}

// class Many {
//     public function __construct(
//         private array $value = [],
//     ) {}

//     public function then(Closure $mapper) {
//         return new self(flatMap($this->value, $mapper));
//     }

//     public function value() {
//         return $this->value;
//     }

//     public function __get(string $name) {
//         return $this->then(fn($item) => $item->$name);
//     }
// }

$genres = [
    new Genre('Science Fiction', [
        new Author('Douglas Adams', [
            new Book(
                'Hitchhiker\'s Guide To The Galaxy',
                'In the beginning the Universe was created. This
                has made a lot of people very angry and been widely
                regarded as a bad move...',
            ),
        ]),
    ]),
];

var_dump(array_filter(getAllWordsFor($genres)));

3-fluent.php

<?php

class Config {
    private string $appName;
    private string $timeZone;

    public function appName(string $value = null) {
        if (is_null($value)) {
            return $this->appName;
        }

        $this->appName = $value;
        return $this;
    }

    public function timeZone(string $value = null) {
        if (is_null($value)) {
            return $this->timeZone;
        }

        $this->timeZone = $value;
        return $this;
    }

    // public function __call($name, array $parameters) {
    //     if (property_exists($this, $name)) {
    //         if (is_null($name)) {
    //             return $this->$name;
    //         }

    //         $this->$name = $parameters[0];
    //     }

    //     return $this;
    // }
}

class Fluent {
    public function __construct(private $decorated) {}

    public function then($name, $value = null) {
        return (function() use ($name, $value) {
            if (property_exists($this, $name)) {
                if (is_null($value)) {
                    return $this->$name;
                }

                $this->$name = $value;
            }

            return new Fluent($this);
        })->call(clone $this->decorated);
    }

    public function value() {
        return $this->decorated;
    }

    // public function __call($name, array $parameters) {
    //     return $this->then($name, ...$parameters);
    // }
}

$config = new Config();
$config->appName('testing');
$config->timeZone('CET');

// $config = (new Fluent(new Config));
// $config = $config->then('appName', 'testing');
// $config = $config->then('timeZone', 'CET');

// $config = (new Fluent(new Config));
// $config = $config->appName('testing');
// $config = $config->timeZone('CET');

var_dump($config);