anchor.diff:                                           {error, atom()}.
   update(Ref, Id, Function) ->
       gen_server:call(Ref, {update, Id, Function}, infinity).
  +
  +%% @doc Update all objects given a mutation function.
  +-spec update_all(ref(), function()) -> {ok, term()}.
  +update_all(Ref, Function) ->
  +    gen_server:call(Ref, {update_all, Function}, infinity).
   
   %% @doc Retrieve a record from the backend.
   -spec get(ref(), id()) -> {ok, variable()} | {error, not_found} |
  
positive.code:             Error
      end,
      {reply, Result, State};
  handle_call({fold, Function, Acc0}, _From, #state{ref=Ref}=State) ->
      Acc1 = ets:foldl(Function, Acc0, Ref),
      {reply, {ok, Acc1}, State};
  
negative.code: -export([start/1,
           put/3,
           update/3,
           update_all/2, %% @todo add this function to behaviour lasp_storage_backend
           get/2,
           reset/1,
           fold/3]).
  