code: func addToPurse(purse *MemoryPurse, name, path string) error {
  	f, err := os.Open(path)
  	if err != nil {
  		return err
  	}
  	defer f.Close()
  	b, err := ioutil.ReadAll(f)
  	if err != nil {
  		return err
  	}
  	purse.files[name] = string(b)
  	return nil
  }
docs: // addToPurse adds a file to the specified purse with the given name.