anchor.diff:  
   %% Exported helper functions.
   -export([internal_fold/6,
  -         internal_fold_harness/8]).
  +         internal_fold_harness/7]).
   
   %% Exported utility functions.
   -export([next_key/3,
  
positive.code:                                                 AccId,
                                                  BindFun,
                                                  ReadFun,
                                                  undefined,
                                                  undefined]),
      ok.
  
  -spec internal_fold_harness(store(), id(), function(), id(), function(),
                              function(), value(), value()) -> function().
  internal_fold_harness(Variables, Id, Function, AccId, BindFun, ReadFun,
                        PreviousValue, _PreviousAccValue) ->
      %% Blocking threshold read on source value.
      {ok, {Id, Type, Value, _}} = ReadFun(Id,
                                           {strict, PreviousValue},
  
negative.code:     {ok, _} = BindFun(AccId, AccValue, Variables),
  
      internal_fold_harness(Variables, Id, Function, AccId, BindFun,
                            ReadFun, Value).
  
  %% @doc Send responses to waiting threads, via messages.
  %%
  