Define own data structures in OCaml using Make syntax - ocaml

Question

In attempting to implement the exercises from Purely Functional Data Structures in OCaml I'm not sure how I can create instances of my solutions.
Say I have the following code:
module type Stack =
sig
type 'a t
val empty : 'a t
val isEmpty : 'a t -> bool
val cons : 'a -> 'a t -> 'a t
val head : 'a t -> 'a
val tail : 'a t -> 'a t
end
(* Implementation using OCaml lists *)
module MyStack : Stack = struct
type 'a t = 'a list
exception Empty
let empty = []
let isEmpty l =
match l with
| [] -> true
| _ -> false
let cons x l = x :: l
let head l =
match l with
| h :: _ -> h
| [] -> raise Empty
let tail l =
match l with
| _ :: r -> r
| [] -> raise Empty
end
I want to provide a Make function similar to Set.Make(String) for creating a specialised instance.
But I'm not sure how to do that.

Answer 1

Seems to me it's natural to parameterize a set by a notion of order (or you could get away with just equality). But a stack doesn't need to be parameterized in that way; i.e., it doesn't depend on a notion of order or equality. It just depends on algebraic properties of its structure.
You already have a parametrically polymorphic module that can be used to make a stack of any type of object.
I'm looking at the code for the Set module. If you want to make a functor like Set.Make, you need a module type for the elements. Since you can use any type at all (unlike Set, which needs an ordered type), you could use something like this:
module type AnyType = struct type t end
Then your functor might look like this (again, I'm just copying code from the Set module):
module Make(Any: AnyType) =
struct
type elt = Any.t
type t = elt list
...
end
Update
If you just want to try out your stack code as is, you can just start using it:
$ ocaml
OCaml version 4.01.0
# #use "mystack.ml";;
module type Stack =
sig
type 'a t
val empty : 'a t
val isEmpty : 'a t -> bool
val cons : 'a -> 'a t -> 'a t
val head : 'a t -> 'a
val tail : 'a t -> 'a t
end
module MyStack : Stack
# let x = MyStack.cons 3 MyStack.empty;;
val x : int MyStack.t = <abstr>
# MyStack.head x;;
- : int = 3
#