(* acct.sig *)

(* bank accounts with a non-negative integer balances *)

signature ACCT =
sig

(* type of bank accounts *)

type acct

(* create a bank account with a balance of 0 *)

val make : unit -> acct

(* exception raised when argument is non-positive *)

exception NonPositive

(* if n <= 0, then incEvt(acct, n) raises NonPositive

   otherwise, incEvt(acct, n) returns an event that, when synchronized
   with, increments acct's current balance by n *)

val incEvt : acct * int -> unit CML.event

(* if n <= 0, then decEvt(acct, n) raises NonPositive

   otherwise, decEvt(acct, n) returns an event that, when synchronized
   with, which is only possible if acct's balance is at least n,
   decrements acct's balance by n *)

val decEvt : acct * int -> unit CML.event

end;