Re: [Caml-list] about Obj.magic

[dengping zhu <zhudp@cs.bu.edu>]

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.

Regards,
Dengping





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

>Hi,
>
>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.
>
>-- 
>Daniel de RAUGLAUDRE
>daniel.de_rauglaudre@inria.fr
>http://cristal.inria.fr/~ddr/
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