anchor.diff:                  end
               end
           end,
  +
  +    % ArgEvaluator returns fun for finding specific operation in list and evaluation
  +    % of it's args
  +    % For example:
  +    %    Specs = [#operation{name = rate, args = RateArgs}, #operation{name = time, args = TimeArgs}],
  +    %    F = ArgEvaluator(time, Specs, undefined),
  +    %    {ArgsRes, State2} = F(State1) % Evaluates TimeArgs and returns results as ArgsRes
  +    %
  +    % We use these funs in order to reevaluate some key loop parameters (like
  +    % rate) while executing loop because vars values could be changed at any
  +    % moment. So, for instance, instead of passing Rate to a loop function, we
  +    % pass function that evaluates Rate as soon as we need it.
  +
       ArgEvaluator =
           fun (Name, Spec, Default) ->
               case lists:keyfind(Name, #operation.name, Spec) of
  
positive.code: 
  eval_rates(#const_rate{rate_fun = F, value = Prev} = RateState, Done, CurTime, _Time, State) ->
      {Rate, State1} = F(State),
      NewDone =
          case {Rate, Prev} of
              {Prev, _} -> Done;
  
negative.code: -spec eval([proplists:property()], [script_expr()], worker_state(), worker_env(), module())
      -> {script_value(), worker_state()}.
  eval(LoopSpec, Body, State, Env, WorkerProvider) ->
      % Evaluator returns fun for evaluation of specific expression
      % For example:
      %     F = Evaluator(Expr),
      %     {Res1, State2} = F(State1), % evaluates expression Expr
      %     {Res2, State3} = F(State2)  % evaluates expression Expr again
  
      Evaluator =
          fun (Expr) ->
              fun (S) ->
  