anchor.diff:  code_change(_OldVsn, State, _Extra) ->
       {ok, State}.
   
  +killer(KillCmd) ->
  +    receive _ ->
  +        os:cmd(KillCmd)
  +    after 1000 ->
  +        ?MODULE:killer(KillCmd)
  +    end.
  +
  
positive.code: -behaviour(gen_server).
  
  -export([start_link/1, start_link/2, start_link/3, stop/1]).
  -export([set_timeout/2, prompt/2, prompt_many/2]).
  -export([send/2, writeline/2, readline/1, writejson/2, readjson/1]).
  -export([init/1, terminate/2, handle_call/3, handle_cast/2, handle_info/2, code_change/3]).
  
  
negative.code:             % this ensure the real os process is killed when this process dies.
              erlang:monitor(process, Pid),
              receive _ -> ok end,
              killer(?b2l(KillCmd))
          end),
      OsProc =
      lists:foldl(fun(Opt, Proc) ->
  