public function files()
    {
        $files = [];
        foreach (call_user_func($this->callable) as $file) {
            $path = $this->scanner->find($file);
            if ($path === false) {
                throw new RuntimeException("Could not locate {$file} for {$this->callable} in any configured path.");
            }
            $files[] = new Local($path);
        }
        return $files;
    }