Functional.php

<?php
namespace x3\Functional;

use x3\Functional\ArgPlaceholder as _;

class Functional
{
    /**
     * Return the method with reversed argument order
     *
     * @param callback $method The method to reverse
     *
     * @return closure The reversed method
     */
    public static function reverseArgs($method)
    {
        return function () use ($method) {
            return call_user_func_array($method, array_reverse(func_get_args()));
        };
    }
    /**
     * Curry `$callback` with the passed arguments
     *
     * @param callable $callback The callback to curry
     * @param mixed $arg ... The arguments to add by default
     *
     * @return closure The curried function
     */
    public static function curry($callback)
    {
        $curryArgs = array_slice(func_get_args(), 1);
        $argsCallback = function ($args, $arg) {
            $placeHolderIndex = array_search((string)new _, $args);
            if ($placeHolderIndex !== false) {
                $args[$placeHolderIndex] = $arg;
            } else {
                $args[] = $arg;
            }

            return $args;
        };

        return function () use ($callback, $curryArgs, $argsCallback) {
            $args = array_reduce(func_get_args(), $argsCallback, $curryArgs);
            return call_user_func_array($callback, $args);
        };
    }

    public static function compose()
    {
        $callables = array_reverse(func_get_args());
        $callback = function ($arg, $callable) {
            return call_user_func($callable, $arg);
        };

        return function ($parameter) use ($callables, $callback) {
            return array_reduce($callables, $callback, $parameter);
        };
    }

    public static function memoize($callable)
    {
        $store = [];

        return function () use ($callable, &$store) {
            $args = func_get_args();
            $key = json_encode($args);

            if (!isset($store[$key])) {
                $store[$key] = call_user_func_array($callable, $args);
            }

            return $store[$key];
        };
    }
}