JoCaml

type coins = Nickel | Dime and drinks = Coffee | Tea and buttons = BCoffee | BTea | BCancel;;   (* def defines a Join-pattern alternatives set clause    * '&' in the left side of '=' means join (channel synchronism)    * '&' in the right hand side is parallel processing    * synchronous_reply :== "reply" [x] "to" channel_name    * synchronous channels have function-like types (`a -> `b)    * while asynchronous ones have type `a Join.chan    * only the last statement in a pattern rhs expression can be an asynchronous message    * 0 in an asynchronous message position means STOP ("no sent message" in CSP terminology).    *)   def put(s) = print_endline s ; 0 (* STOP *)    ;; (* put: string Join.chan *)   def give(d) = match d with                  Coffee -> put("Coffee")                  | Tea -> put("Tea")               ;; (* give: drink Join.chan *)   def refund(v) = let s = Printf.sprintf "Refund %d" v in put(s)      ;; (* refund: int Join.chan *)   let new_vending give refund =   let vend (cost:int) (credit:int) = if credit >= cost                       then (true, credit - cost)                       else (false, credit)   in   def coin(Nickel) & value(v) = value(v+5) & reply to coin   or coin(Dime) & value(v) = value(v+10) & reply to coin     or button(BCoffee) & value(v) =       let should_give, remainder = vend 10 v in      (if should_give then give(Coffee) else 0 (* STOP *))               & value(remainder) & reply to button     or button(BTea) & value(v) =       let should_give, remainder = vend 5 v in      (if should_give then give(Tea) else 0 (* STOP *))               & value(remainder) & reply to button     or button(BCancel) & value(v) = refund( v) & value(0) & reply to button   in spawn value(0) ;   coin, button  (* coin, button: int -> unit *)   ;; (* new_vending: drink Join.chan -> int Join.chan -> (int->unit)*(int->unit) *)   let ccoin, cbutton = new_vending give refund in   ccoin(Nickel); ccoin(Nickel); ccoin(Dime);    Unix.sleep(1); cbutton(BCoffee);    Unix.sleep(1); cbutton(BTea);    Unix.sleep(1); cbutton(BCancel);   Unix.sleep(1) (* let the last message show up *)   ;;