[Caml-list] Exceptions and at_exit

[Caml-list] Exceptions and at_exit

[David Fox]

I have some at_exit functions that must execute before my program
exits, but I also want to see a traceback of any exception that
occurs.  Can I catch the exception, print a traceback like the one you
get when you exit and then call exit?  Or can I catch the exception,
execute the at_exit functions, and then re-raise the exception?  How
*do* you re-raise an exception, anyway?  Do you just catch the
exception and raise it?
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Re: [Caml-list] Exceptions and at_exit

[Remi VANICAT]

David Fox <david@lindows.com> writes:

> I have some at_exit functions that must execute before my program
> exits, but I also want to see a traceback of any exception that
> occurs.  Can I catch the exception, print a traceback like the one you
> get when you exit and then call exit?  Or can I catch the exception,
> execute the at_exit functions, and then re-raise the exception?  How
> *do* you re-raise an exception, anyway?  Do you just catch the
> exception and raise it?


for reraising an exception :

try
  foo bar
with
  x ->
    baaz buz;
    raise x

but i don't know if this work well with traceback.
-- 
Rémi Vanicat
vanicat@labri.u-bordeaux.fr
http://dept-info.labri.u-bordeaux.fr/~vanicat
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Re: [Caml-list] Exceptions and at_exit

[David Fox]

David Fox <david@lindows.com> writes:

> I have some at_exit functions that must execute before my program
> exits, but I also want to see a traceback of any exception that
> occurs.  Can I catch the exception, print a traceback like the one you
> get when you exit and then call exit?  Or can I catch the exception,
> execute the at_exit functions, and then re-raise the exception?  How
> *do* you re-raise an exception, anyway?  Do you just catch the
> exception and raise it?

My confusion about re-raising exceptions was caused by the fact that
you get different behavior if you say something like

  try ... with
    Failure msg -> <do some stuff>; raise (Failure msg)

vs something like

  try ... with
    exn ->
       begin match exn with Failure msg -> <do some stuff> end;
       raise exn

In the second case, you are re-raising the exception, in the first
you are raising a new exception and your original traceback is lost.
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Re: [Caml-list] Exceptions and at_exit

[William Lovas]

On Sat, Jul 13, 2002 at 06:30:23AM -0700, David Fox wrote:
> My confusion about re-raising exceptions was caused by the fact that
> you get different behavior if you say something like
> 
>   try ... with
>     Failure msg -> <do some stuff>; raise (Failure msg)
> 
> vs something like
> 
>   try ... with
>     exn ->
>        begin match exn with Failure msg -> <do some stuff> end;
>        raise exn
> 
> In the second case, you are re-raising the exception, in the first
> you are raising a new exception and your original traceback is lost.

What if you did something like:

    try ... with
        Failure msg as exn -> <do some stuff>; raise exn

Would that leave the original traceback intact?

William
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Re: [Caml-list] Exceptions and at_exit

[Xavier Leroy]

> What if you did something like:
> 
>     try ... with
>         Failure msg as exn -> <do some stuff>; raise exn
> 
> Would that leave the original traceback intact?

Yes -- provided <some stuff> doesn't raise exceptions.  The trace back
mechanism relies on reference equality (==) on exception values: if
the program raises an exception that is == to the latest exception
raised, this is considered as a "re-raise" and adds to the traceback;
otherwise, it's considered as an "initial raise" and a fresh traceback is
started.

- Xavier Leroy
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