anchor.diff:          Err -> Err
       end. 
   
  +handle_fib_command(Arg) ->
  +    case try_parse_int(Arg) of
  +        {ok, Int} when Int < 100 -> F = fib(Int), {ok, io_lib:format("~p", [F])};
  +        {ok, _Int} -> {error, floodgate};
  +        Err -> Err
  +    end.
  +
   handle_fac_command(Arg) ->
       case try_parse_int(Arg) of
           {ok, Int} when Int < 101 -> F = fac(Int), {ok, integer_to_list(F)};
  
positive.code:     case Tokens of
          ["fac", Arg] -> 
              H = handle_fac_command,
              MFA = {Mod, H, [Arg]},
              apply_command(From, To, MFA);
          ["fmt", Fmt, Arg] ->
  
negative.code: 
  %% handlers
  -export([handle_fac_command/1,
           handle_fib_command/1,
           handle_roll_command/2,
           handle_fmt_command/2,
           handle_fread_command/2]).
  