module type SHOW =
sig
  type t
  val show : t -> string
end

let print (implicit Show : SHOW) x = Show.show x

implicit module ShowInt = struct type t = int let show = string_of_int end
implicit module ShowFloat = struct type t = float let show = string_of_float end

implicit functor ShowPair (Show1 : SHOW) (Show2 : SHOW) =
struct
  type t = Show1.t * Show2.t
  let show (x, y) = "(" ^ Show1.show x ^ ", " ^ Show2.show y ^ ")"
end

let rec grow1 : (implicit Show : SHOW) -> Show.t -> 'a =
  fun (implicit Show : SHOW) x -> grow1 (x, x)
(*
Characters 494-538:
    fun (implicit Show : SHOW) x -> grow1 (x, x);;
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: This expression has type (implicit Show : SHOW) -> 'b -> 'a
       but an expression was expected of type
         (implicit Show : SHOW) -> Show.t -> 'a
       This instance of Show.t is ambiguous:
       it would escape the scope of its equation
*)