JoCaml

Example

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 *)
 ;;

$ jocamlcexample.ml-otest
$ ./test
Coffee
Tea
Refund 5

See also

References

External links