anchor.diff:      apply(CBModuleName, FunName, Args).
   
   
  +%% call to a callback module
  +%% wraps some common functionaly of all calls to callback modules, like inserting
  +%% the respective callback module's state and unpacking the ModuleName/InstanceId tuple
   -spec cb_call(FunName, Arguments, Msg, CBModule, State) -> Return when
       is_subtype(FunName, cb_fun_name()),
       is_subtype(Arguments, list()),
  
positive.code:      ].
  
  
  -spec contains(Element::any(), List::list()) -> boolean().
  contains(_Element, []) -> false;
  
  
negative.code:        H =/= Element -> contains(Element, List)
      end.
  
  
  %% Returns a list as string
  -spec to_string(list()) -> string().
  to_string(List) when is_list(List) ->
      lists:flatten(io_lib:format("~w", [List])).
  