Anonymous Function, Closure, আর Callback

$greet = function ($name) {
    return "Hello, $name!";
};

echo $greet('Sam');   // Hello, Sam!

$taxRate = 0.08;

$addTax = function ($price) use ($taxRate) {
    return $price * (1 + $taxRate);
};

echo $addTax(100);   // 108

$numbers = [1, 2, 3, 4, 5];

$doubled = array_map(function ($n) {
    return $n * 2;
}, $numbers);
// [2, 4, 6, 8, 10]

$evens = array_filter($numbers, function ($n) {
    return $n % 2 === 0;
});
// [2, 4]

function factorial(int $n): int {
    if ($n <= 1) {
        return 1;
    }
    return $n * factorial($n - 1);
}

echo factorial(5);   // 120

function sum(...$numbers): int {
    return array_sum($numbers);
}

echo sum(1, 2, 3);        // 6
echo sum(1, 2, 3, 4, 5);  // 15

function makeUser(string $name, string $role = 'user', bool $active = true) {
    // ...
}

makeUser(name: 'Sam', active: false);
// role এর default মান রাখে, active স্পষ্টভাবে সেট করা — ক্রম গুরুত্বপূর্ণ না