code: func writeIDs(idsList []id, outfile string) error {
  	data, err := json.Marshal(idsList)
  	if err != nil {
  		return err
  	}
  	data = append(data, '\n')
  
  	if outfile != "" {
  		return ioutil.WriteFile(outfile, data, 0644)
  	}
  
  	fmt.Printf("%s", data)
  	return nil
  }
docs: // The `writeIDs` function produces a file containing JSON serialized
  // contact objects