(* default values *)
let somebool = ref false
let somestr = ref ""
let someint = ref 0

let usage = "usage: " ^ Sys.argv.(0) ^ " [-b] [-s string] [-d int]"

let speclist = [
    ("-b", Arg.Set somebool, ": set somebool to true");
    ("-s", Arg.Set_string somestr, ": what follows -s sets some string");
    ("-d", Arg.Set_int someint, ": some int parameter");
  ]

let () =
  (* Read the arguments *)
  Arg.parse
    speclist
    (fun x -> raise (Arg.Bad ("Bad argument : " ^ x)))
    usage;

  Printf.printf " %b %d '%s'\n" !somebool !someint !somestr;
;;