English version
Accueil     À propos     Téléchargement     Ressources     Contactez-nous    

Ce site est rarement mis à jour. Pour les informations les plus récentes, rendez-vous sur le nouveau site OCaml à l'adresse ocaml.org.

Browse thread
[Caml-list] about Obj.magic
[ Home ] [ Index: by date | by threads ]
[ Search: ]

[ Message by date: previous | next ] [ Message in thread: previous | next ] [ Thread: previous | next ]
Date: 2002-05-31 (15:39)
From: dengping zhu <zhudp@c...>
Subject: Re: [Caml-list] about Obj.magic
Hi, thanks for all you guys. 

After carefully checking my code, I tried to remove Obj.magic from my
code. Anyway, at last I have to keep one which is not the case you guys
mentioned. My code is very simple:

type ty = ty1 -> ty2   

(* where ty1, ty2 are some types I defined before, ty1 is some type like
g * h, while ty2 likes c * d * e * f. *)

let x = (f (g)) a

Here, f and g are functions, and the return type of (f (g)) is ty, which
is a function type ty1 -> ty2. While, the type of a is ty1. So, the
return type of (f (g)) a should be ty2. Anyway, every time I get an
error here. The error message is: You applied too many parameters... 

I was very surprised. After I removed a, then it is all right and the
return type is ty. So, I was thinking that the compiler treated ty as an
atomic type, not a function type. Then I have to use 'Obj.magic' here.
Anyway, the result with 'Obj.magic' is correct.

Probablely I was wrong here, but I'd like to get the help from you.


On Fri, 31 May 2002, Daniel de Rauglaudre wrote:

>On Thu, May 30, 2002 at 05:09:43PM -0400, dengping zhu wrote:
>> When should I use 'Obj.magic'? It is really confusing. Now I am
>> converting a bunch of code from sml to ocaml. [...]
>About conversion from SML into OCaml, I may help: these days, I am
>trying to convert a program of 70000 lines of SML into OCaml, using
>Camlp4. Please ask me if you want more details.
>About examples of use Obj.magic, there are the extensible grammars of
>Camlp4, and in particular the EXTEND function. I can explain here if
>people are interested. And I know that the OCaml toplevel program uses
>it also.
>In general, like Jacques Garrigue said, don't use Obj.magic if you are
>not *absolutely* sure of what you do.
>To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
>Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
>Beginner's list: http://groups.yahoo.com/group/ocaml_beginners

To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners