How to get a backtrace out of ocaml

backtrace.ml

(*******************************************************************************

   Getting a backtrace out of ocaml is not completely obvious. You
   have to compile the code with -g and then run with OCAMLRUNPARAM=b,
   like this:

   $ ocamlc -g -o test test.ml
   $ OCAMLRUNPARAM=b ./test
   backtrace_status: true
   Failure("nth")
   Raised at file "pervasives.ml", line 32, characters 22-33
   Called from file "test.ml", line 20, characters 10-29
   Called from file "test.ml", line 29, characters 4-10

 ******************************************************************************)

open Printf

let bar () =
  let i = List.nth [1;2;3] 10 in (* raise Not_found *)
  printf "This should not print %d\n" i

let foo () =
  bar ()

let () =
  try
    printf "backtrace_status: %b\n" (Printexc.backtrace_status ());
    foo ()
  with e ->
    printf "%s\n" (Printexc.to_string e);
    Printexc.print_backtrace stdout