$add = function ($valone,$valtwo) {
    return $valone + $valtwo;
};
$add(1,2) // 3

$y = 1;
$fn = function ($x) use ($y) {
    return $x + $y;
};
echo $fn(2); // 3

$y = 1;
$fn = fn($x) => $x + $y;
echo $fn(2); // 3

class foo {
   public function test() {
       $context = fn($thethis) => var_dump($thethis);
       $context($this);
   }
}
$test = new foo();
$test->test(); // object(foo)#1 (0) { }

$y = 1;
$fn = fn() => $y++;
$fn(); // Has no effect
echo $y  // 1

fn(int $x) => $x; // the argument type must be (int)
fn(): int => $x; // type of return value (int)

$var = 10;
$int_fn = fn(int $x): int => $x;
var_dump($int_fn($var)); // int(10)
try {
    $int_fn("foo");
} catch (TypeError $e) {
    echo $e->getMessage(), "n"; // Argument 1 passed to {closure}() must be of the type int, string given, called in x on line y
}

$funn = fn(?int... $args): array => $args;
var_dump($funn(20, null, 30)); // Array(3) { [0]=> int(20) [1]=> NULL [2]=> int(30) }

$var = 6;
var_dump((fn() => fn() => $var)()());  // int(6)
var_dump((fn() => function() use($var) { return $var; })()()); // int(6)

ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);
$b = 1;
fn() => $b + $c; // no error, nothing


ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);
$b = 1;
(fn() => $b + $c)(); // Notice: Undefined variable: c in the location on line x