tester.ex

defmodule Tester do
  def run(input) do
    with {:ok, widget} <- process_widget(input) do
      do_something_with_widget(widget) #noop
  else
    {:error, reason} ->
      #something with reason
  end
  
  @spec process_widget(input :: binary) :: {:ok, contents :: binary} | {:error, reason :: binary}
  def process_widget(input) do
    with {:ok, contents} <- File.read(input),
         {:ok, decoded} <- Jason.decode(contents) do
       {:ok, decoded}
    else 
      error ->
        {:error, "Received error"}
    end
  end
end