On Apr 3, 2008, at 10:07, Hezekiah M. Carty wrote:

> On Thu, 03 Apr 2008, Jacques Garrigue wrote:
>
>> From: "Hezekiah M. Carty" <hcarty@atmos.umd.edu>
>>> Is this possible, either from the C or OCaml side without making  
>>> the callback associate with "foo" an option type (use  
>>> (Callback.register "foo" (Some some_func)) to set a callback and  
>>> (Callback.register "foo" None) to clear it)?
>>
>> Since Callback.register has type: string -> 'a -> unit you are not  
>> limited by the ocaml type system. So you can reset your value with
>>  Callback.register "foo" 0
>> and check for equality with Val_int(0) on the C side. (Note that  
>> you must initialize the value to 0 at program startup, because the  
>> default for an unitialized value is 0 which is not Val_int(0))
>
> If I wrap the C interface in an OCaml module, would it be enough to  
> include:
>
> let () = Callback.register "foo" 0
>
> in the top level of the module to have this command execute when the  
> module is loaded?  Or does the module user have to do some explicit  
> initialization?


I've used this technique, although I did have initialization ordering  
problems. The outer module is not necessarily initialized before the  
inner one. In my case, the initialization was idempotent, so I simply  
repeated it in each submodule.

— Gordon