I have a function which takes a module as an argument. That module must implement certain callbacks.  My use-case is completely analogous to starting a genserver with a callback module.  I was thinking it would be nice to check that the module given actually implemented the correct behaviour. I arrived at the following solution.   @spec start_link({module, term}, options) :: {:ok, endpoint}   def start_link(app = {mod, _}, options) do     mod.module_info[:attributes]     |> Keyword.get(:behaviou...