type counter = { mutable i: int};;
let mutable a = 0;;
let flip0 () = (a <- (1 - a)); (printf "%i\n" a);;

let flip =
  let c:counter = { i = 0 }
  fun () -> (c.i <- 1 - c.i); (printf "%i\n" c.i);;

let flip2 =
  let c:counter = { i = 0 }
  fun () -> (c.i <- 1 - c.i); (printf "%i\n" c.i);;

let make_flipper = fun () ->
  let c:counter = { i = 0 }
  fun () -> (c.i <- 1 - c.i); (printf "%i\n" c.i)