(** Functions which implement useful operations not related to any
    particular type *)

val and_then : (unit -> 'a) -> (unit -> 'b) -> 'a
  (** [and_then f g] - evaluate [f] and then evaluate [g], even if [f]
      raises an exception.  Return the value that [f] returned. *)
val stopwatch : (unit -> 'a) -> float * 'a
  (** [stopwatch f] - evalute [f] and return its result value and the
      number of seconds that elapsed during its evaluation.  *)
val index : (int -> bool) -> int -> int -> int
  (** [index f min max] - pass integers to f starting with min and
      continuing until we reach max, and return the first one [i] for
      which [f i] is true. *)
val wrap : (unit -> unit) -> (unit -> 'a) -> (unit -> unit) -> 'a
  (** [wrap before thunk after] - Somewhat misguided extension of
      and_then. *)

exception Timeout
val do_locked :
  ?timeout:int ->
  ?waitfn:(int -> bool -> unit) -> string -> (unit -> 'a) -> 'a
  (** [do_locked ?timeout ?waitfn lockfile f] - Execute [f] while
      holding a [lockfile] containing our process ID.  If we can't
      create [lockfile], see if the process that created it is still
      alive.  If not, break the lock.  If it is, call [waitfn] up to
      [timeout] times. *)