Performance tests of implementing reduce in PHP.

ReduceImplementations.php

<?php

function add($a, $b) {
    return $a + $b;
}

function foldl(array $array, $function, $initial) {
    if (empty($array)) {
        return $initial;
    }
    $head = array_shift($array);
    return call_user_func(__FUNCTION__, $array, $function, $function($initial, $head));
}

function foldLeft(array $array, $function, $initial) {
start:

    if (empty($array)) {
        return $initial;
    }
    $initial = $function($initial, array_shift($array));
    goto start;
}

function foldr(array $array, $function, $initial) {
    if (empty($array)) {
        return $initial;
    }
    $head = array_pop($array);
    return call_user_func(__FUNCTION__, $array, $function, $function($initial, $head));
}

function foldRight(array $array, $function, $initial) {
start:
    if (empty($array)) {
        return $initial;
    }
    $initial = $function($initial, array_pop($array));
    goto start;
}

function reduce(array $array, $function, $initial) {
    $carry = $initial;
    foreach ($array as $item) {
        $carry = $function($carry, $item);
    }
    return $carry;
}


$i = 0;
define('ITERATIONS', 100);
$data = range(1, 999);
$initial = 500;

$algorithms = array('foldl', 'foldLeft', 'foldr', 'foldRight', 'array_reduce', 'reduce');
foreach ($algorithms as $algorithm) {
    $start = microtime(TRUE);
    for ($i = 0; $i < ITERATIONS; $i++) {
        call_user_func($algorithm, $data, 'add', $initial);
    }
    $stop = microtime(TRUE);
    printf("Algorithm %s took %f seconds.\n", $algorithm, $stop - $start);
}