anchor.diff:  %%% non-negative integers, and EOF is -1.
   %%%
   %%% TODO:
  -%%% - output ports
   %%% - textual-port stuff
   %%% - binary-port stuff
   
  
positive.code:     [] -> {ok, false}; % alas, io: doesn't support non-blocking peeks
      _Ch -> {ok, true}
    end.
  
negative.code: 	 open_input_string/1,
  	 open_stdin/0]).
  
  -export([write_char/2,
  	 close_output_port/1,
  	 open_stdout/0]).
  
  command(Pid, Cmd) ->
    MonRef = erlang:monitor('process', Pid),
  