safe_unsafe.ml

type (_,_) safety = Safe : ('a,'a option) safety  | Unsafe : ('a,'a) safety

let ios: type a. (int, a) safety -> string -> a = fun safety s ->
  match safety with
  | Safe -> (try Some (int_of_string s) with _ -> None)
  | Unsafe -> int_of_string s

let () =
  assert (ios Safe "dskljf" = None);
  (try
    ignore (ios Unsafe "dskljf"); assert false
  with _ -> ());
  assert (ios Safe "42" = Some 42);
  ()