lists.php

<?php
$empty = function($selector) {
    return $selector(null, null, true);
};

$prepend = function($el, $list) {
    return function($selector) use ($el, $list) {
        return $selector($el, $list, false);
    };
};

$head = function($list) {
    return $list(function($h, $t, $e) {
        return $h;
    });
};

$tail = function($list) {
    return $list(function($h, $t, $e) {
        return $t;
    });
};

$is_empty = function($list) {
    return $list(function($h, $t, $e) {
        return $e;
    });
};

$list = $prepend("asdf", $empty);
var_dump($head($list));