Functional Piping in PHP

pipes.php

<?php declare(strict_types = 1);

function pipe(...$args) {
    return function ($arg) use ($args) {
        $reducer = function ($prev, $fn) {
            return $fn($prev);
        };

        return array_reduce($args, $reducer, $arg);
    };
}

function pipeWith($arg, ...$fns) {
    return pipe(...$fns)($arg);
}

$odds = function (array $a): array {
    return array_filter($a, function ($x) {
        return $x % 2 !== 0;
    });
};

$double = function (array $a): array
{
    return array_map(function ($x) {
        return $x * 2;
    }, $a);
};

$log = function (array $a): array {
    echo implode(', ', $a);

    return $a;
};

$data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

// These are functionally same and print out '2, 6, 10, 14, 18'
pipe($odds, $double, $log)($data);
pipeWith($data, $odds, $double, $log);