(*** Here are a few things to investigate if you're learning ocaml *)

(*** "**" in opening comment, for ocamldoc *)
(** simple-clock.ml
   Repeatedly prints the current time at the standard output,
   at intervals of 1 sec

   How to compile:

   ocamlopt unix.cmxa simple-clock.ml -o simple-clock
*)

(*** You don't need to open the module if you qualify names with "Unix." *)
(*open Unix*)

(*** It's not important in such a simple program, but you can hide
     functions like print_tm that are used only by one other function *)
(*let print_tm tm =
  print_int tm.tm_hour;
  print_char ':';
  print_int tm.tm_min;
  print_char ':';
  print_int tm.tm_sec
*)

let simple_clock () =
  let print_tm tm =
    (*** so you don't get "7:8:9" *)
    Printf.printf "%2d:%02d:%02d\n"
                        tm.Unix.tm_hour tm.Unix.tm_min tm.Unix.tm_sec;
    flush stdout in
  (*** This works, but in ocaml you can do it in a more functional style *)
(*  while true do
    print_tm (Unix.localtime (Unix.time ()));
    print_newline ();
    ignore (Unix.select [] [] [] 1.0)
  done
*)
  let rec loop () =
    print_tm (Unix.localtime (Unix.time ()));
    ignore (Unix.select [] [] [] (1. -. (fst (modf (Unix.gettimeofday ())))));
    loop () in
  loop () in
simple_clock ()

(*let _ = simple_clock ()*)

(*** It's easier to read if you remove my comments and the code that
     I've commented out. Have fun *)