continuations.ml

module Continuation : sig
  type ('a, 'r) t = ('a -> 'r) -> 'r

  val return : 'a -> ('a, 'r) t
  val (>>=) : ('a, 'r) t -> ('a -> ('b, 'r) t) -> ('b, 'r) t
end = struct
  type ('a, 'r) t = ('a -> 'r) -> 'r

  let return x = fun k -> k x

  let (>>=) m f = fun k ->
    m (fun a -> (f a) k)
end


module Continuation' : sig
  type 'a t = { run : 'r . ('a -> 'r) -> 'r}

  val return : 'a -> 'a t
  val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
end = struct
  type 'a t = { run : 'r . ('a -> 'r) -> 'r}

  let return x = { run = fun k -> k x}

  let (>>=) m f =
    let run k =
      m.run (fun a -> (f a).run k)
    in
    { run }
end