open Lexing

let concat lb1 lb2 =
  { lb1 with refill_buff =
    let in_lb2 = ref false in
    fun lb ->
      if !in_lb2 then lb2.refill_buff lb
      else begin
    lb1.refill_buff lb;
    if lb.lex_eof_reached
    then begin
      in_lb2 := true;
      lb.lex_buffer      <- lb2.lex_buffer;
      lb.lex_buffer_len  <- lb2.lex_buffer_len;
      lb.lex_abs_pos     <- lb2.lex_abs_pos;
      lb.lex_start_pos   <- lb2.lex_start_pos;
      lb.lex_curr_pos    <- lb2.lex_curr_pos;
      lb.lex_last_pos    <- lb2.lex_last_pos;
      lb.lex_last_action <- lb2.lex_last_action;
      lb.lex_eof_reached <- lb2.lex_eof_reached;
      lb.lex_mem         <- lb2.lex_mem;
      lb.lex_start_p     <- lb2.lex_start_p;
      lb.lex_curr_p      <- lb2.lex_curr_p;
      lb2.refill_buff lb
    end
      end
  }

let rec read lexbuf =
  lexbuf.refill_buff lexbuf;
  print_string lexbuf.lex_buffer;
  if lexbuf.lex_eof_reached then print_string "\nDone reading.\n"
  else read lexbuf

let () = read (concat (from_channel stdin) (from_string "\nEND OF INPUT\n"))