let rec read_byte (i, last) =
  try
    let x = input_char stdin in
    if (String.length i) > 0 && (last = x) then read_byte (i, last)
    else read_byte (i ^ (String.make 1 x), x)
  with
  | End_of_file -> i;;

read_byte ("", '\x00') |> print_string; print_newline ();;