"ocaml_beginners"::[] quick question on mutually recursive types

how do i make a class obj containing a Set of obj? it's like the
chicken and egg problem - if i first instantiate the module, obj is
undefined, but if i first define the class, i haven't instantiated
the Set yet. thanks in advance for any help.

Messages in this topic (1) Reply (via web post) | Start a new topic

.

On Mon, Mar 05, 2007 at 08:22:16AM -0000, overbored wrote:
> how do i make a class obj containing a Set of obj? it's like the
> chicken and egg problem - if i first instantiate the module, obj is
> undefined, but if i first define the class, i haven't instantiated
> the Set yet. thanks in advance for any help.

Do you need to use objects? A much more natural way to express this
in functional languages is:

type 'a thing = Thing of 'a | List of 'a thing list

Example usage:

# let w1 = Thing 1;;
val w1 : int thing = Thing 1
# let w2 = Thing 2;;
val w2 : int thing = Thing 2
# let things = List [w1; w2];;
val things : int thing = List [Thing 1; Thing 2]

If you really want a set (ie. no duplicates) then it's a little bit
more complicated.

Rich.

--
Richard Jones
Red Hat UK Limited

Messages in this topic (2) Reply (via web post) | Start a new topic

.

On Monday 05 March 2007 08:22, overbored wrote:
> how do i make a class obj containing a Set of obj? it's like the
> chicken and egg problem - if i first instantiate the module, obj is
> undefined, but if i first define the class, i haven't instantiated
> the Set yet. thanks in advance for any help.

You must use mutually recursive modules:

# module rec A : sig
type t = <get: ASet.t>
val compare : t -> t -> int
end = struct
type t = <get: ASet.t>
let compare = compare
end
and ASet : Set.S = Set.Make(A);;
module rec A : sig type t = < get : ASet.t > val compare : t -> t -> int end
and ASet : Set.S

However, as Richard has said you are probably using the wrong tool for the
job. Try posting problems rather than proposed solutions without the problem
and you'll probably get more helpful advice.

--
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
OCaml for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists

Messages in this topic (3) Reply (via web post) | Start a new topic

.

I'd really like to play around ocamldefun, but it seems to only work
with ocaml 3.06. Has anyone had luck setting this up in more recent
versions of ocaml?

Messages in this topic (8) Reply (via web post) | Start a new topic

.

On Thursday 08 March 2007 19:18, Sasha Rush wrote:
&gt; I'd really like to play around ocamldefun, but it seems to only work
>; with ocaml 3.06. Has anyone had luck setting this up in more recent
&gt; versions of ocaml?

Isn't it just a preprocessor for OCaml code, so you can feed any OCaml code
through it independent of the compiler?

--
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
OCaml for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists

Messages in this topic (9) Reply (via web post) | Start a new topic

.

On Mar 8, 2007, at 2:30 PM, Jon Harrop wrote:

> On Thursday 08 March 2007 19:18, Sasha Rush wrote:
&gt;> I'd really like to play around ocamldefun, but it seems to only work
>;> with ocaml 3.06. Has anyone had luck setting this up in more recent
&gt;> versions of ocaml?
&gt;
> Isn't it just a preprocessor for OCaml code, so you can feed any
> OCaml code
>; through it independent of the compiler?
>

I'm having trouble just compiling it. It requires claims it requires
3.06.

> --
> Dr Jon D Harrop, Flying Frog Consultancy Ltd.
>; OCaml for Scientists
> http://www.ffconsultancy.com/products/ocaml_for_scientists
>
>;
> ------------------------ Yahoo! Groups Sponsor --------------------
> ~-->
> Check out the new improvements in Yahoo! Groups email.
&gt; http://us.click.yahoo.com/4It09A/fOaOAA/yQLSAA/saFolB/TM
&gt; ----------------------------------------------------------
> ~->
&gt;
> Archives up to November 11, 2006 are also downloadable at http://
> www.connettivo.net/cntprojects/ocaml_beginners/
&gt; The archives of the very official ocaml list (the seniors' one) can
> be found at http://caml.inria.fr
> Attachments are banned and you're asked to be polite, avoid flames
> etc.
>; Yahoo! Groups Links
&gt;
>
>
>;

Messages in this topic (10) Reply (via web post) | Start a new topic

.