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Date: -- (:)
From: Sylvain Le Gall <sylvain@l...>
Subject: Re: OCaml/C variant representation
Hello,

On 24-02-2010, Jean Yang <jeanyang@csail.mit.edu> wrote:
> Hello,
>
>   I'm having some trouble with variant representation in the OCaml/C
> interface.
>
>   According to the reference I found (
> http://caml.inria.fr/pub/docs/manual-ocaml/manual032.html), it seems like if
> we have value v = variant VConstr(val), where val is some integer value,
> should have Field(val, 0) == hash_variant("VConstr") and Int_val(Field(v, 0)
>== val.  I don't seem to be understanding this correctly, since I am getting
> Int_val(Field(v, 0)) == val.
>
>   I have the following datatype declaration in my OCaml:
> type newty = VConstr of int | ...
> In the C implementation of OCaml function foo : newty -> int, I have
> something like this;
>   CAMLprim value foo (value v) {  ... }
> In the body of this function I am looking at the fields of val.  Am I doing
> something wrong here?
>

Please have a look at:
http://caml.inria.fr/mantis/view.php?id=4803

This section is misleading. You should use hash_variant for `VConstr.

In your case VConstr of int will be Block with size = 1 and tag = 0;
first non-constant constructor and first field contains Value_int(...)

Regards
Sylvain Le Gall