(* Example: conventional arrays and locks *)

#load "libarray"

module A = Array

(* The first array example. *)
let deposit (a: int A.array) (acct: int) (amount: int) =
  A.set a acct (A.get a acct + amount)

(* Alms doesn't provide locks, since MVars are strictly better,
 * but for the sake of example: *)
module type LOCK = sig
  type lock
  val new : unit -> lock
  val acquire : lock -> unit
  val release : lock -> unit
end

module Lock : LOCK = struct
  type lock = unit MVar.mvar
  let new = MVar.new
  let acquire = MVar.take
  let release (mv: lock) = MVar.put mv ()
end

(* The array example with locks. *)
let deposit' (a: int A.array) (acct: int) (amount: int)
             (lock: Lock.lock) =
  Lock.acquire lock;
  A.set a acct (A.get a acct + amount);
  Lock.release lock