Re: general purpose C++ exception handler in lisp

Grégory,

Yes, indeed I would like something like "handler-case" but for C++
exceptions instead of common lisp conditions.  I understand that some SBCLs
handle C++ exceptions like win32, because the OS requires that the
executable handle them.  I'm not sure about unix implementations of SBCL,
but I specifically need to be able to gracefully handle the exception at
the location I choose, and not somewhere at the beginning of the stack.  So
I was hoping someone who might have some experience setting up C++
exception handlers at various places in a stack, and on various OSes could
chime in and give a rundown of how doable this may be, but I don't think
anyone is listening.

-AKW

On Wed, Feb 12, 2025 at 3:07 AM Grégory Vanuxem <[email protected]> wrote:

> Hi Andrew,
>
> I respond to you question because I use libjulia.* (julialang.org) with
> "does-not-catch-exceptions/errors-let-my-underlying-lisp-catch-an-handle-them".
> And to add more uncertainty and to start with, I am not a real CL coder I
> do what I can. Do you mean something like:
>
> (defun divide (numerator denominator)
>   (handler-case
>       (/ numerator denominator)
>     (division-by-zero ()
>       (format t "Error: Division by zero is not allowed."))))
>
> (Copilot generated, do not burn me please ;)) No tested code frankly but I
> guess the important keyword for you is 'handler-case'. The SBCL source code
> has easily finding files(s) that handle floating point exceptions to handle
> them. This is another subject, more linked to the material, but that can
> give you some hints).
>
> - Greg
>
> Le sam. 8 févr. 2025 à 21:49, Andrew Wolven <[email protected]> a écrit :
>
>> I'm working with some rather large C++ libraries.
>>
>> In the past, I have written C wrappers for C++ calls, which inside the
>> wrapper, uses a C++ try/catch form which catches any exception (...) and
>> calls a lisp callback function which signals a lisp error.
>>
>> It would behoove my build process and [possibly] reduce complexity if I
>> could get rid of the C wrappers and call the C++ methods directly from Lisp
>> with the ffi.
>>
>> The problem is, these C++ methods sometimes throw exceptions.  It would
>> be really cool if I had a macro, like 'with-try/catch' where I could set up
>> a C++ exception handler frame, and execute the body of the macro, which is
>> lisp code, but most likely contains a foreign function call to a C++ method
>> which can throw.
>>
>> The catch portion could translate the C++ exception into a lisp condition
>> and signal the lisp condition.  I don't think I would rethrow if a
>> translation is not found, but rather signal a general C++-error lisp
>> condition.
>>
>> I've seen some posts which indicate that something like this may be
>> doable on Windows (windows amd64 is my primary platform), but it would also
>> be good if it worked on Linux and Macos.
>>
>> Does anyone have thoughts on how I could implement such a macro?
>>
>> Thanks,
>> Andrew Wolven
>> _______________________________________________
>> Sbcl-help mailing list
>> [email protected]
>> https://lists.sourceforge.net/lists/listinfo/sbcl-help
>>
>

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