Need help with a range function (Ocaml)

[Gnu/Vince]

let range ?(l_lim=0) (u_lim) ?(step=1) =
let rec loop n l =
if n = (pred l_lim) then l
else loop (n - step) (n::l)
in

loop (u_lim - 1) []


let print_int_list l =

print_string "[ ";
List.iter (fun n ->
print_int n;
print_char ' ') l;
print_endline "]"


let _ =

try
let l = range (int_of_string Sys.argv.(1)) in
print_int_list l
with
| Failure "int_of_string" ->
print_endline "So long.";
exit 1;
| Invalid_argument "Array.get" ->
print_endline "So long.";
exit 1


Since I'm pretty sure eventually Jeremy will look at this thread, here's the output of the compile command:


% ocamlc fill3.ml -o fill3
File "fill3.ml", line 1, characters 36-37:
Warning: This optional argument cannot be erased
File "fill3.ml", line 25, characters 19-20:
This expression has type ?step:int -> int list but is here used with type
int list



Can you help me?

[Gnu/Vince]

Also, I would like to thank/congratulate Jeremy for contributing to the proof-reading of the english version of the O'Reilly book of Objective Caml.
http://caml.inria.fr/oreilly-book/