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Message-ID: <ad8cfe7e0603042131q3ab6af1focdb6fc8272e4c0a5@mail.gmail.com>
Date: Sun, 5 Mar 2006 18:31:53 +1300
From: "Jonathan Roewen" <jonathan.roewen@gmail.com>
To: "David Powers" <david@grayskies.net>
Subject: Re: [Caml-list] Looking for suggestions on self-referential object definitions
Cc: caml-list@inria.fr
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	version=3.0.3

> class virtual item =3D
>   object (self)
>     val mutable name =3D ""
>
>     method name =3D name
>
>     method set_name newname =3D name <- newname
>   end
> ;;
>
>
> class weapon =3D
>   object (self)
>     inherit item
>   end
> ;;
>
>
> class container =3D
>   object (self)
>     inherit item
>
>     val mutable items =3D []
>
>     method add newitem =3D items <- (newitem :: items)
>
>     method contents =3D items
>
>     method remove i =3D items <- List.filter (fun x -> x !=3D i) items
>
>     method contents_to_string =3D
>       let print_item i =3D
>         match i with
>           | `Weapon w -> Printf.sprintf "%s (weapon)" w#name
>           | `Container c -> Printf.sprintf "%s (container) -
> Containing:\n%s" c#name c#contents_to_string
>       in
>         List.map print_item items
>
>   end
> ;;

First off, method contents_to_string has conflicting types to be
recursive. Second, adding a type constraint to items should fix your
problems.

My changes:

class container =3D
  .....
    val mutable items : [ `Weapon of weapon | `Container of container
] list =3D []
  ...
    method contents_to_string =3D
       .....
        List.fold_left (fun a b -> if a =3D "" then print_item b else a
^ "; " ^ print_item b) "" items

  end
;;

Jonathan