ocaml良さ

main.ml

type 'a myList = MyNil | MyCons of 'a * 'a myList

let rec print_mylist l =
    match l with
      | MyCons(head, tail) -> 
        print_string(head);
        print_mylist(tail);
      | MyNil -> print_string("nil") 
      
let () =
  print_mylist (MyCons("xxx", MyNil))
let () =
  print_mylist (MyNil)

main2.ml

type 'a myList = MyNil | MyCons of 'a * 'a myList

let rec map f x = 
  match x with
    | MyNil -> MyNil
    | MyCons (x, xs) ->
      MyCons (f x, map f xs);
;;
map print_string MyNil
;;
map print_string (MyCons("xxx", MyNil))
;;