defmacro defkv(kv) do
  quote do
    Enum.each unquote(kv), fn {k, v} ->
      def unquote(k)(), do: unquote(v)
    end
  end
end

If you try to run our new macro, you will notice it won’t even compile, complaining that the variables k and v does not exist. This is because of the ambiguity: unquote(k) can either be an unquote fragment, as previously, or a regular unquote as in unquote(kv).

文档里有一处修改是这样的，这里的 ambiguity 怎么理解？ 这两种情况是什么？