anchor.diff:  %%   Msg -> [Actions]
   %% to
   %%   {SenderPid, Msg} -> {SenderPid, Msg, [Actions]}
  -%%
  -%% (temporarily Msg -> {Msg, [Actions]})
   transform_receive_clause(Clause) ->
       [OldPattern] = erl_syntax:clause_patterns(Clause),
       OldGuard = erl_syntax:clause_guard(Clause),
  
positive.code: 	    MapFun = fun(T) -> instrument_toplevel(T) end,
  	    Transformed = erl_syntax_lib:map_subtrees(MapFun, Tree),
  	    Abstract = erl_syntax:revert(Transformed),
  	    io:put_chars(erl_prettypr:format(Abstract)),
  	    NewForms = erl_syntax:form_list_elements(Abstract),
  	    {ok, NewForms};
  	{error, Error} -> {error, Error}
  
negative.code: 		    error
  	    end;
  	{error, Error} ->
  	    log:log("error: ~p~n", [Error]),
  	    %% Delete `used` table.
  	    ets:delete(used),
  	    error
  