let p s n = print_string (s^string_of_int n^"\n"); flush stdout

(*version 1*)
class ['a,'b] acc f init = object
    val mutable v = (init:'a)
    val func = (f:'a -> 'b -> 'a)
    method app x =
	let newX = func v x in
	v <- newX;newX
end

let f1 = new acc (+) 0

let _ = p "f1:" (f1#app 1)
let _ = p "f1:" (f1#app 1)
let _ = p "f1:" (f1#app 1)

(*version 2*)
class ['a,'b] acc' f init = object
    inherit ['a,'b] acc f init
    method init x = v <- x
end

let f2 = new acc' (+) 0

let _ = p "f2:" (f2#app 1)
let _ = p "f2:" (f2#app 1)
let _ = p "f2:" (f2#app 1)
let _ = f2#init (-5)
let _ = p "f2:" (f2#app 1)
let _ = p "f2:" (f2#app 1)
let _ = p "f2:" (f2#app 1)