Handle custom errors (OCaml)

handlecustomerrors.ml

exception Foo of string

let main () =
  print_endline "Running";
  raise (Foo "Something went wrong")

let handle_errors f () =
  Printexc.register_printer
    (function
      | Foo msg ->
        Some (Printf.sprintf "Something foo: %s" msg)
      | _ -> None
    );
  try
    Unix.handle_unix_error main ()
  with e ->
    let msg = Printexc.to_string e in
    Printf.printf "Error. %s\n%!" msg;
    exit 1

let () = handle_errors main ()