Co-fondateur de Quantic Telecom

Thibaud Dauce sur YouTube

La programmation fonctionnelle

pour les développeuses·eurs web

Il y a 3 ans…

Haskell c'est quoi ?

• pas de conditions
• pas de boucles
• pas de variables

function getStudents() {
    $customers = Customer::all();
    $students = [];
 
    foreach($customers as $customer) {
        if ($customer->isStudent()) {
            $students[] = $customer;
        }
    }
 
    return $students;
}

function getStudents() {
    $customers = Customer::all();
    
    return array_filter($customers, function ($customer) {
        return $customer->isStudent();
    });
}

function getStudents() {
    return Customer::all()
        ->filter(function ($customer) {
            return $customer->isStudent();
        });
}

function getStudents() {
    $customers = Customer::all();
    
    return array_filter(array_filter($customers, function ($customer) {
        return $customer->isStudent();
    }), function ($student) {
        return $student->isValid();
    });
}

function getStudents() {
    return Customer::all()
        ->filter(function ($customer) {
            return $customer->isStudent();
        });
        ->filter(function ($student) {
            return $customer->isValid();
        });
}

function getMonthlyMeanRevenueForStudents() {
    $customers = Customer::all();
    $totalRevenue = [];
    $counts = [];
 
    foreach($customers as $customer) {
        if ($customer->isStudent()) {
            foreach($customer->invoices() as $invoice) {
                $totalRevenue[$invoice->month()] +=
                    $invoice->total();
                $counts[$invoice->month()]++;
            }
        }
    }
 
    $meanRevenue = [];
    foreach ($totalRevenue as $month => $total) {
        $meanRevenue[$month] = $total / $counts[$month];
    }
 
    return $meanRevenue;
}

function getMonthlyMeanRevenueForStudents() {
    return Customer::all()
        // [
        //     'Étudiant John',
        //     'Étudiante Jane',
        //     'Entreprise Google',
        // ]
        ->filter(function ($customer) {
            return $customer->isStudent();
        })
        // [
        //     'Étudiant John',
        //     'Étudiante Jane',
        // ]
        ->map(function ($student) {
            return $student->invoices();
        })
        // [
        //     ['2019-03-001', '2019-04-001'],
        //     ['2019-03-002'],
        // ]
        ->flatten()
        // [ '2019-03-001', '2019-04-001', '2019-03-002']
        ->groupBy(function ($invoice) {
            return $invoice->month();
        })
        // [
        //     '2019-03' => ['2019-03-001', '2019-03-002'],
        //     '2019-04' => ['2019-04-001'],
        // ]
        ->map(function ($invoices) {
            // = ['2019-03-001', '2019-03-002']// = [80, 100]// = 180// = 90
            return $invoices->map(function ($invoice) {
                return $invoice->total();
            })->sum() / $invoices->count();
        });
        // [
        //     '2019-03' => 90,
        //     '2019-04' => 150,
        // ]
}

function getMonthlyMeanRevenueForStudents() {
    $customers = Customer::all();
    $totalRevenue = [];
    $counts = [];
 
    foreach($customers as $customer) {
        if ($customer->isStudent()) {
            foreach($customer->invoices() as $invoice) {
                $totalRevenue[$invoice->month()] +=
                    $invoice->total();
                $counts[$invoice->month()]++;
            }
        }
    }
 
    $meanRevenue = [];
    foreach ($totalRevenue as $month => $total) {
        $meanRevenue[$month] = $total / $counts[$month];
    }
 
    return $meanRevenue;
}

PHP RFC: Arrow Functions 2.0

function getMonthlyMeanRevenueForStudents() {
    return Customer::all()
        ->filter(fn($customer) => $customer->isStudent())
        ->flatMap(fn($student) => $student->invoice())
        ->groupBy(fn($invoice) => $invoice->month())
        ->map(function ($invoices) {
            $total = $invoices
                ->map(fn($invoice) => $invoice->total())
                ->sum();
            return $total / $invoices->count();
        });
}

Middlewares

Gestion d'une Chaîne de traitement

Requête HTTP → Réponse HTTP

3 problèmes

• Vérifiez que la personne est connectée
• Ajouter un header HTTP à toutes les réponses
  (Content-Language: fr)
• Enregistrer le temps de traitement d'une requête

function myMiddleware(Request $request, $next): Response
{
    // $next = function (Request $request): Response {
    //      return new Response(200, 'All good!');
    // };

    $response = $next($request);
    return $response;
}

Vérifiez que la personne est connectée

function authMiddleware(Request $request, $next): Response
{
    if (! $request->session()->has('user')) {
        return new Response(302, '/login');
    }

    $response = $next($request);
    return $response;
}

Ajouter un header HTTP à chaque réponse

function contentLanguageMiddleware(Request $request, $next): Response
{
    $response = $next($request);

    $response->headers()->add('Content-Language', 'fr');

    return $response;
}

Enregistrer le temps de traitement d'une requête

function timeMiddleware(Request $request, $next): Response
{
    $start = microtime(true);
    
    $response = $next($request);

    $time = microtime(true) - $start;
    $text = "Request {$request->url()} took {$time}s \n";
    file_put_content('timings.txt', $text, FILE_APPEND);

    return $response;
}

Exemples de middlewares avec Laravel

$middlewares = [
    CheckForMaintenanceMode::class,
    EncryptCookies::class,
    StartSession::class,
    ThrottleRequests::class,
    ConvertEmptyStringsToNull::class,
];

L'ordre des middlewares

$middlewares = [
    'authMiddleware',
    'contentLanguageMiddleware',
    'timeMiddleware',
];

$middlewares = [
    'timeMiddleware',
    'authMiddleware',
    'contentLanguageMiddleware',
];

function otherMiddleware(ClasseA $classeA, $next): ClasseB
{
    // $next = function (ClasseA $classeA): ClasseB {
    //      return new ClasseB;
    // };

    $classeB = $next($classeA);
    return $classeB;
}

Un peu de Front-End

Elm

MVU

Model View Update

Model

type alias Model = String

init : Model
init = "Thibaud"

Update

type Event = NewName String | Reverse

update : Event -> Model -> Model
update event oldName = case event of
    NewName newName -> newName
    Reverse -> String.reverse oldName

View

view : Model -> Html Event
view name =
    div []
        [ input [ placeholder "New Name", onInput NewName, value name ] []
        , button [ onClick Reverse ] [ text "Reverse Name" ]
        , div [] [ text name ]
        ]

elm-lang.org

D'autres ressources

• Refactoring to Collection
• Haskell Book
• PureScript
• Ma chaîne YouTube « Thibaud Dauce »

Merci à tous