anchor.diff:  
   set_env(Config, Mod, Env) ->
       OldEnvs = Config#config.envs,
  -    NewEnvs = case lists:keymember(Mod, 1, OldEnvs) of
  -                  true  -> lists:keyreplace(Mod, 1, OldEnvs, {Mod, Env});
  -                  false -> [{Mod,Env}|OldEnvs]
  -              end,
  +    NewEnvs = dict:store(Mod, Env, OldEnvs),
       Config#config{envs=NewEnvs}.
   
   get_env(Config, Mod) ->
  -    proplists:get_value(Mod, Config#config.envs, []).
  +    dict:fetch(Mod, Config#config.envs).
   
   %% ===================================================================
   %% Internal functions
  
positive.code:     lists:reverse(Acc);
  local_opts([Item | Rest], Acc) ->
      local_opts(Rest, [Item | Acc]).
  
negative.code: 
  -record(config, { dir :: file:filename(),
                    opts = [] :: list(),
                    envs = new_env() :: dict() }).
  
  %% Types that can be used from other modules -- alphabetically ordered.
  -export_type([config/0]).
  