See https://twitter.com/b_viguier/status/1408861287677935627

example.php

<?php

// Factorial of a number
printf("\nype a number: ")
&& ($g = (int) trim(fgets(STDIN))) && (fn(int $g, $y) =>
    printf($y(static fn (callable $function) => static fn ($n = 1) => (1 >= $n) ? 1 : $n * $function($n - 1))($g))
)(
    $g,
    static fn (callable $g): callable => (static fn ($f): callable => $f($f))(static fn ($f): callable => $g(static fn ($x) => $f($f)($x)))
);

// Collatz/Syracuse conjecture
printf("\nType a number: ")
&& ($g = (int) trim(fgets(STDIN))) && (fn($g, $y) =>
    $y(static fn (callable $loop) => static fn (int $n) => printf('%s,', $n) && (1 === $n ? 1 : $loop(0 === $n % 2 ? $n / 2 : $n * 3 + 1)))($g)
)(
    $g,
    static fn (callable $g): callable => (static fn ($f): callable => $f($f))(static fn ($f): callable => $g(static fn ($x) => $f($f)($x)))
);