[Caml-list] Declaring a parameterized type in a .mli

[William Smith <bills@emu-bark.com>]

Hi

I'm trying to create a generic ID module so that it is easy to make 
multiple distinct ID classes.   I want to be able to create sets and 
maps of them so I've made my signature compatible with Set.Make but I'm 
not making it that far yet.  I want to have one class of IDs for NFA 
states and another for DFA states etc. and I want to reuse the code when 
I find I need other ID classes.

Here's what I've got in my .mli:

module IDRoot :
sig
end

module GenericID ( Root : sig end ) :
sig
     type t
     val compare : t -> t -> int
     val to_string : t -> string
     val cons : unit -> t
end

module Id = GenericID( IDRoot )

I get a syntax error even though I think I am following the reference 
books online.  The error is on the equal sign of the last line:

File "broken.mli", line 13, characters 10-11:
Error: Syntax error

(For each class of IDs I will declare another IDRoot but with a 
different name.)   Is there a better way?  This one seems really simple 
if I could correct the syntax error.

Thanks for any help you can offer.

Bill Smith