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Subject: [Caml-list] Undefined_recursive_module
Date: Mon, 26 Jul 2004 20:23:06 -0500
Message-ID: <CC62E8B84E918E438D0BA094D9AF417903D5E3D2@MSPM1BMSGM12.ent.core.medtronic.com>
Thread-Topic: Undefined_recursive_module
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From: "Hawkins, Thomas" <thomas.d.hawkins@medtronic.com>
To: <caml-list@inria.fr>
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I just started experimenting with recursive modules, but have hit a snag =
with Undefined_recursive_module.

Basically I need to define an ADT where the data structure contains Sets =
and the Set elements reference back to the data structure.  In the =
following example, the mutually recursive modules include the main data =
structure (Process), an ordered type (Files), and a set (FileSet =
returned from the Set functor).

Both the Process and the File modules define only function values, =
therefore I believe the example satisfies the "safe module" requirement. =
 It does compile and run for one case (see does_work).  However, if I =
make multiple calls to Process.add_file, Undefined_recursive_module is =
raised (see does_not_work).

Any suggestions?  (I'm using 3.08.0)

Thanks,

Tom






module rec Process :
  sig
    type t
    val create    : unit -> t
    val add_file  : File.t -> t -> unit=20
    val print     : t -> unit
  end
  =3D
  struct
    type t =3D { mutable files : FileSet.t }
   =20
    let create () =3D
      { files =3D FileSet.empty }

    let add_file file process =3D
      process.files <- FileSet.add file process.files

    let print process =3D
      FileSet.iter File.print process.files
  end

and File :
  sig
    type t
    val compare   : t -> t -> int
    val create    : Process.t -> string -> t
    val print     : t -> unit
  end
  =3D
  struct
    type t =3D Process.t * string

    let compare a b =3D
      match a, b with (_, a), (_, b) -> String.compare a b

    let create process name =3D
      process, name

    let print (_, name) =3D
      print_string name;
      print_newline ()
  end

and FileSet :
  Set.S with type elt =3D File.t
  =3D
  Set.Make(File)
;;



let does_work () =3D
  let p =3D Process.create () in
  Process.add_file (File.create p "file1") p;
  Process.print p
;;


let does_not_work () =3D
  let p =3D Process.create () in
  Process.add_file (File.create p "file1") p;
  Process.add_file (File.create p "file2") p;
  Process.print p
;;


(*
does_work ();;
*)
does_not_work ();;

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