public function getHelper($name)
    {
        if (! $this->hasHelper($name)) {
            throw new Exceptions\HelperNotFound($name);
        }

        if (! isset($this->helpers[$name])) {
            $factory = $this->helperMap[$name];
            $this->helpers[$name] = $factory();
        }

        return $this->helpers[$name];
    }