anchor.diff:  pcompose_loop([], [Failure], _) ->
       Failure;
   pcompose_loop([], Failures, _) ->
  +    ?D_LOG("pcompose_loop/3: failures are ~p~n", [Failures]),
       {fail, 
        {multiple_failures, 
         lists:foldl(fun({fail, {multiple_failures, Ls}}, Acc) ->
  
positive.code: -type validator_result() :: ('ok' | {'fail', _}).
  -type validator() :: fun((wallaroo_tree:tree(), module()) -> validator_result()).
  -export_type([validator_result/0, validator/0]).
  
  succeed(_Tree, _StoreMod) ->
      ok.
  
negative.code: 	{result_for, Pid, ok} ->
  	    handle_success(Pid, Pids, Failures, Failfast);
  	{result_for, Pid, {fail, _}=Failure} ->
  	    ?D_LOG("got a failure:  ~p~n", [Failure]),
  	    handle_failure(Pid, Pids, Failure, Failures, Failfast);
  	X ->
  	    ?D_LOG("got something unexpected:  ~p~n", [X]),
  	    handle_failure(unknown, Pids, {fail, {other_validator_result, X}}, Failures, Failfast)	    
      end.
  
  