(* Example: arrays with fractional capabilities *)

module type FRACTIONAL = sig
  type ('a,'b) array
  type 1
  type 2
  type 'c / 'd
  type ('b,'c) cap : A

  val new   : int → 'a →
                ∃'b. ('a,'b) array × ('b,1) cap
  val get   : ('a,'b) array → int →
                ('b,'c) cap → 'a × ('b,'c) cap
  val set   : ('a,'b) array → int → 'a →
                ('b,1) cap → ('b,1) cap

  val split : ('b,'c) cap → ('b,'c/2) cap × ('b,'c/2) cap
  val join  : ('b,'c/2) cap × ('b,'c/2) cap → ('b,'c) cap
end

#load "libarray"
module A = Array

module Fractional : FRACTIONAL = struct
  type ('a,'b) array = 'a A.array
  type 1
  type 2
  type 'c / 'd
  type ('b,'c) cap = unit

  let new (size: int) (init: 'a) : ∃'b. ('a,'b) array × ('b,1) cap =
    (A.new size init, ())

  let get (ar: 'a A.array) (ix: int) _ = (A.get ar ix, ())
  let set (ar: 'a A.array) (ix: int) (new: 'a) _ =
    A.set ar ix new

  let split _ = ((), ())
  let join  _ = ()
end