# 鶩 defmodule Duck do defstruct name: nil end # 犬 defmodule Dog do defstruct name: nil end # 猫 defmodule Cat do defstruct name: nil end # 鳴くプロトタイプ defprotocol Sound do def sound(_) end # 鶩が鳴く実装 defimpl Sound, for: Duck do …