[Ocaml-lib-devel] Re: OCaml dumper

[Richard J. <ri...@an...>]

On Wed, Feb 09, 2005 at 12:09:02AM +0200, Anatoly Zaretsky wrote:
> Hi!
> 
> I was playing with this nice tool and I want to suggest some additions to it.
> 
> First, I think pointers (out-of-heap ones too) can be (portably I
> hope) dumped like this:
> 
> let fieldval x =
>   let ni = 0n in
>     Obj.set_field (Obj.repr ni) 1 x;
>     ni;;
> 
> let hex_of_field x = Printf.sprintf "%0*nx" (Nativeint.size / 4) (fieldval x);;
> 
> Then, custom blocks contain pointer to their ops structure in the
> first field, which can be used to determine their type. This way
> "standard" custom values can be recognized and printed:
> 
> let with_obj f x = f (Obj.obj x)
> let cust_ops x = Obj.field x 0
> let (custom_printers : (Obj.t, Obj.t -> string) Hashtbl.t) =
> Hashtbl.create 5 (* printer functions hashed with ops struct pointer
> values *)
> let pr_pair (v : 'a) (f : 'a -> string) = cust_ops (Obj.repr v), with_obj f
> 
> List.iter (fun (v, f) -> Hashtbl.add custom_printers v f)
>   [
>     pr_pair Int32.zero (Printf.sprintf "%ldl");
>     pr_pair Int64.zero (Printf.sprintf "%LdL");
>     pr_pair Nativeint.zero (Printf.sprintf "%ndn")
>   ]
> 
> let add_printer v f =
>   let v', f' = pr_pair v f in
>     Hashtbl.add custom_printers v' f'
> and print_custom x = Hashtbl.find custom_printers (cust_ops x) x
> 
> For example:
> # print_custom (Obj.repr 765n);;
> - : string = "765n"
> # print_custom (Obj.repr (-765l));;
> - : string = "-765l"
> # print_custom (Obj.repr (-7659876655443438L));;
> - : string = "-7659876655443438L"
> 
> It seems that get_list guarded with is_list is redundant - one can write
>     if is_list r then ( (* List. *)
>       let fields = obj r in (* or (obj r : t list) for purity ;) *) in
>     ...
>     )
> instead.
> 
> Similarly for arrays:
>     else if t = 0 || t = double_array_tag then ( (* Tuple, array, record. *)
>       let fields = Array.to_list (obj r) in (* float arrays and
> records work fine! *)
> 
> For constructed values similar trick can be used.
> 
> Hope this will be helpful.
> 
> P.S. And thanks for the great tutorial on OCaml! I learnt OCaml this
> summer mostly from it (with INRIA manual and O'Reilly book of course
> ;) ). For-loops in the cerebellum are the best :)
> 
> -- 
> Best regards,
> Tolik

-- 
Richard Jones, CTO Merjis Ltd.
Merjis - web marketing and technology - http://merjis.com
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