PHPのアロー関数で代入やif分岐できない制限を回避

fn.php

<?php

$let = fn(...$a) => array_pop($a)(...$a);

$v1 = 10;

$let($v1 + 1, fn($v2) => 
$let($v2 + 1, fn($v3) =>
$let($v3 + 1, fn($v4) => 
	var_dump($v1, $v2, $v3, $v4)
)));

/*
int(10)
int(11)
int(12)
int(13)
*/

$null = fn() => null;
$if = fn($c, $t, $f=null) => $c ? $t() : ($f ?? $null)();

$x = 1;
$y = -1;

var_dump(
	$if($x === 0,
		fn() => 1,
		fn() => 2,
	)
);

var_dump(
	$if($x < 0,
		fn() => $if($y < 0,
			fn() => 1,
			fn() => 2,
		),
		fn() => $if($y < 0,
			fn() => 3,
			fn() => 4,
		)
	)
);

var_dump(
	$if($x === 1,
		fn() => 1,
	$if($x === 2,
		fn() => 2,
	$if($x === 3,
		fn() => 3,
	)))
);

/*
int(2)
int(3)
int(1)
*/