reify.ml

(* Step 1: 'a list -> bool everywhere. *)

(* Step 2: Wrap in a newtype: Finder of 'a list -> bool *)

(* Step 3: abstract in a module with this signature *)

module type LIST_FINDER = sig
  type 'a t

  val this_element : 'a -> 'a t

  val find : 'a t -> 'a list -> bool
end

(* And this implementation *)

module Before : LIST_FINDER = struct
  type 'a t = Finder of ('a list -> bool)

  let this_element x = Finder (List.mem x)

  let find (Finder f) l = f l
end

(* Step 4: invert constructor and deconstructor *)

module After : LIST_FINDER = struct
  type 'a t = 'a

  let this_element x = x

  let find x l = List.mem x l
end