anchor.diff:      catch
   	CallbackMode ->
   	    callback_mode_result(S, CallbackMode);
  -	error:undef ->
  -	    %% Process undef to check for the simple mistake
  -	    %% of calling a nonexistent state function
  -	    %% to make the undef more precise
  -	    case erlang:get_stacktrace() of
  -		[{Module,callback_mode,[]=Args,_}
  -		 |Stacktrace] ->
  -		    {error,
  -		     {undef_callback,{Module,callback_mode,Args}},
  -		     Stacktrace};
  -		Stacktrace ->
  -		    {error,undef,Stacktrace}
  -	    end;
   	Class:Reason ->
   	    {Class,Reason,erlang:get_stacktrace()}
       end.
  
positive.code:     try
  	case CallbackMode of
  	    state_functions ->
  		erlang:apply(Module, State, [Type,Content,Data]);
  	    handle_event_function ->
  		Module:handle_event(Type, Content, State, Data)
  	end
  
negative.code:     catch
  	Result ->
  	    {ok,Result,S};
  	Class:Reason ->
  	    {Class,Reason,erlang:get_stacktrace()}
      end.
  