with.ex

result = case File.read("my_company/employees.json") do
  {:ok, contents} ->
    case Poison.decode(contents) do
      {:ok, json} ->
        case Dict.fetch(json, "Peter") do
          {:ok, data} -> {:ok, data}
          :error -> {:error, :key_not_found}
          # Notice the Dict API doesn't return error with reason.
          # So we add a reason to make it conform.
        end
      {:error, reason} -> {:error, reason}
    end
  {:error, reason} -> {:error, reason}
end

result =
  with {:ok, contents} <- File.read("my_company/employees.json"),
       {:ok, json} <- Poison.decode(contents),
       {:ok, data} <- Dict.fetch(json, "Peter") do
    {:ok, data}
  else
    {:error, reason} -> {:error, reason}
    :error -> {:error, :key_not_found}
  end