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  1.  
  2. open Batteries
  4. type init_param =
  5. | Int of int
  6. | Float of float
  8. module type N = sig
  9. type t
  10. val make: init_param -> t
  11. val add_to_self: t -> t -> unit
  12. val as_string: t -> string
  13. end
  15. module Int: N = struct
  16. type t = int ref
  17. let make = function
  18. | Int i -> ref i
  19. | _ -> invalid_arg "make"
  20. let add_to_self x y = x := !x + !y
  21. let as_string = (!) |- Printf.sprintf "%di"
  22. end
  24. module Float: N = struct
  25. type t = float ref
  26. let make = function
  27. | Float f -> ref f
  28. | _ -> invalid_arg "make"
  29. let add_to_self x y = x := !x +. !y
  30. let as_string = (!) |- Printf.sprintf "%gf"
  31. end
  33. let parse: string -> (module N) * init_param = fun s ->
  34. if String.exists s "." then
  35. (module Float: N), Float (float_of_string s)
  36. else
  37. (module Int: N), Int (int_of_string s)
  39. let do_repetitive_work: (module N with type t = 'a) -> 'a -> init_param -> 'a =
  40. fun (type a) m (x: a) i ->
  41. let module C = (val m: N with type t = a) in
  42. let y = C.make i in
  43. C.add_to_self y x;
  44. C.add_to_self y (C.make i);
  45. y
  47. let () = if !Sys.interactive then () else
  48. let m, i = parse Sys.argv.(1) in
  49. let module C = (val m: N) in
  50. let x = C.make i in
  51. do_repetitive_work (module C: N with type t = C.t) x i
  52. |> C.as_string
  53. |> Printf.printf "%s\n"
  54.  
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