継続渡し形式への変換例

cps.ml

(* Example of Continuation Passing Style *)
(* cf. http://practical-scheme.net/docs/cont-j.html *)

type tree =
    Leaf
  | Node of int * tree * tree
;;

let rec sum_nodes t =
  match t with
  | Leaf -> 0
  | Node (i, l, r) ->
      i + (sum_nodes l) + (sum_nodes r)
;;

let rec sum_nodes_cps t cont =
  match t with
  | Leaf -> (cont 0)
  | Node (i, l, r) ->
      sum_nodes_cps l (fun n ->
        sum_nodes_cps r (fun m ->
          cont (i + n + m)))
;;

let identity x = x;;

let t1 = Node(8, Node(4, Node(7, Leaf, Leaf), Leaf), Node(5, Leaf, Leaf));;

let r1 = sum_nodes t1;;
let r1_cps = sum_nodes_cps t1 identity;;