test.php

<?php
$funcache = function ($callable) {
    static $backend = [];
    return function () use ($callable, &$backend) {
        $args = func_get_args();
        $key = json_encode($args);
        if (array_key_exists($key, $backend)) {
            return $backend[$key];
        }
        return $backend[$key] = call_user_func_array($callable, func_get_args());
    };
};

$fab = $funcache(function ($num) {
    sleep(1);
    return $num;
});

echo $fab(1);
echo $fab(1);