anchor.diff:  
   -export_type([plt/0]).
   
  --define(VERSION, "0.4").
  +-define(VERSION, "0.5").
   
   -ifdef(TEST).
   -include("purity_plt_tests.hrl").
  
positive.code:                   {K, C} <- keep_consistent(C0, Tn)],
              Cn = assoc_store(cache_key(Options), Rn, C1),
  
              {ok, Plt#plt{table = Tn, cache = Cn,
                           modules = module_dependencies(Tn),
                           checksums = CS}}
           end.
  
  update_checksums(CS1, CS2) ->
  
negative.code: %% @doc Provided a list of files, return a list of modules which depend
  %% on them and should be re-analysed.
  -spec dependent_modules(plt(), files()) -> [module()].
  
  dependent_modules(#plt{table = T}, Filenames) ->
      Ms = ?utils:module_rmap(T),
      uflatten([reachable(module(F), Ms) || F <- Filenames]).
  
  
  