anchor.diff:  
     {ok, ShellState1};
   
  -
  -
  +% mark token list for parsing if all mentioned files can be found
   shell_step( ShellState = #shell_state{ string_buf = "",
                                          token_buf  = [_|_] } ) ->
   
  
positive.code: 
  % TODO: clear import buffer
  
  shell_step( ShellState = #shell_state{ string_buf = "",
                                         token_buf  = [],
                                         token_lst  = [_|_] } ) ->
  
    #shell_state{ token_lst  = TokenLst,
                  import_buf = ImportBuf,
                  def_lst    = DefLst,
                  query_lst  = QueryLst,
                  reply_lst  = ReplyLst } = ShellState,
  
  
negative.code: 
  get_help() ->
    string:join(
      [?BYLW( "help" )++?YLW( " show this usage info" ),
       ?BYLW( "hist" )++?YLW( " show definition history" ),
       ?BYLW( "quit" )++?YLW( " quit the shell" )
  ], "\n" ).
  
  
  