lambda.php

<?php
mb_internal_encoding("UTF-8");

function λ($fn) {
    list($args, $body) = explode('=>', $fn, 2);

    $args = trim($args);
    $args = ltrim($args, '(');
    $args = rtrim($args, ')');

    $body = 'return ' . $body . ';';

    return create_function($args, $body);
}

$xs = [1, 2, 3];
$ys = array_map(λ('$x => $x * 2'), $xs);

print_r($ys);

$adder = λ('($x, $y) => $x + $y');

var_dump($adder(42, 1337));