redux-php-reducer.php

<?php
function countReducer(array $state, $action) {
    switch($action['type']) {
        case INCREMENT_ACTION:
            return array_replace([], $state, ['count' => $state['count'] + 1]);
        case DECREMENT_ACTION:
            return array_replace([], $state, ['count' => $state['count'] - 1]);
        default:
            return $state;
    }
}