Ahh, well this works:

module type M_t = sig
type 'a t = private { x: 'a list }
val uniq_cons: 'a t -> 'a -> 'a t
val empty: unit -> 'a t
end
 
module M : M_t = struct
type 'a t = { x : 'a list }
let uniq_cons lst a = if List.mem a lst.x then lst else { x = a::lst.x }
let empty () = { x = [] }
end
 
let x = M.empty ()
let x = M.uniq_cons x 1
let x = M.uniq_cons x 1
let x = M.uniq_cons x 2
 
let print { M.x=x } = print_endline (
  "[" ^
  String.concat "," (List.map string_of_int x) ^
  "]"
)
;;                                                                            print x
;;

[skaller@pelican] /mnt/user2/work/flx>ocaml xx.ml
[2,1]

-- 
John Skaller, mailto:skaller@users.sf.net
voice: 061-2-9660-0850, 
snail: PO BOX 401 Glebe NSW 2037 Australia
Checkout the Felix programming language http://felix.sf.net



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