public function registerHelper($helperName)
    {
        $className = __CLASS__ . '\\Helper\\' . ucfirst($helperName);
        try {
            $helperInstance = $this->getClassInstance($className);
            if (!$helperInstance instanceof VoltHelperAbstract) {
                throw new InvalidHelperException();
            }
            $this->getCompiler()->addFunction($helperName, $helperInstance->getHelper());
        } catch (\ReflectionException $e) {
            throw new UnknownHelperException(sprintf('Helper \'%s\' does not exist', $helperName));
        } catch (\Exception $e) {
            throw new InvalidHelperException(sprintf('Invalid helper \'%s\'', $helperName));
        }
    }