anchor.diff:  
   eval({char, Char}, _I, _E, _K, _D, _W, T) ->
     {{char, Char}, T};
  +
  +%%-------------------------------------------------------------------------------------
  +%% Sequence
  +%%-------------------------------------------------------------------------------------
  +eval({seq, Eis}, I, E, K, D, W, T) ->
  +  eval_seq(Eis, I, E, K, D, W, T);
   
   %%-------------------------------------------------------------------------------------
   %% Primop
  
positive.code:       eval2(Xi, I, E, K, D, W, T0 + 1);
      _ ->
        {D0, T0}
    end.
  
  %%-------------------------------------------------------------------------------------
  
negative.code:   end.
  
  eval2(Xi, I, E, K, D, W, T) ->
    {D0, T0} = ice_cache:find(Xi, K, D, W, T),
    case D0 of
      {calc, W} ->
        case lists:keyfind(Xi, 1, E) of
          {_, E0} ->
            {D1, T1} = eval(E0, I, E, K, D, W, T0),
            ice_cache:add(Xi, K, D, W, T1, D1);
          false ->
            {error, undefined_identifier, Xi}
        end;
  