module Nothing: Nothingtypet =Nothing0.t
val unreachable_code : t -> 'aNothing.t, a piece of code that has a value of
    type Nothing.t must be unreachable.  In such an unreachable piece of code, one can
    use unreachable_code to give the code whatever type one needs.  For example:
      let f (r : (int, Nothing.t) Result.t) : int =
        match r with
        | Ok i -> i
        | Error n -> Nothing.unreachable_code n
      ;;
    include Identifiable.S
Nothing.t that you wished to make identifiable, but were
    prevented for lack of Identifiable.S here.
    Obviously, of_string and t_of_sexp will raise an exception.
module Stable:sig..end