while.ml

type value = int
type ptr = value ref
type st = unit

type 'a imp =
  | New of value * (ptr -> 'a imp)
  | Read of ptr * (value -> 'a imp)
  | Write of ptr * value * 'a imp
  | While of (st -> bool) * unit imp * 'a imp
  | Return of 'a

let rec interp = function
  | New (v,k) -> fun () -> let p = ref v in interp (k p)
  | Read (p,k) -> let v = !p in interp (k v)
  | Write (p,v,k) -> p := v; interp k