trouble with scm_display_backtrace in guile 1.8.3

trouble with scm_display_backtrace in guile 1.8.3

[René Köcher]

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Hi,

as the subject states I encountered some problems while
trying to get a backtrace for a exception. I'm trying to embedd
guile into a C programm which should catch exceptions at
global scope and print usable error messages and backtraces.

After some searching I got to the code below which works fine
except for backtrace display.. (crashes with wrong-type-arg)

Any help on this is much appreciated, all samples and
documentation I found was targeted at guile 1.6...

======================================================================
#include <stdio.h>
#include <libguile.h>

void continue_init (void *data, int argc, char **argv);
SCM guile_catch_exception (SCM key, SCM args);

int
main (int argc, char **argv)
{
        if (argc < 2)
        {
                fprintf(stderr, "%s 'scheme expression'\n", argv[0]);
                return 1;
        }

        scm_boot_guile(argc, argv, 0);
        return 0;
}

void
continue_init (void *data, int argc, char **argv)
{
        /* NOTE: this is from a guile 1.6 solution but seems not to work */

        /* enable backtraces */
        SCM_DEVAL_P     = 1;
        SCM_BACKTRACE_P = 1;
        SCM_RECORD_POSITONS_P = 1;
        SCM_RESET_DEBUG_MODE;

        /* eval and exit */
        scm_internal_stack_catch(SCM_BOOL_T,
                                 (scm_t_catch_body)scm_c_eval_string,
                                 (void*)argv[1],
                                 (scm_t_catch_handler)guile_catch_exception,
                                 NULL);
}

SCM
guile_catch_exception (SCM key, SCM args)
{
        if (scm_ilength(args) >= 3)
        {
                SCM stack = scm_fluid_ref(
                            SCM_VARIABLE_REF(scm_the_last_stack_fluid_var));
                SCM subr  = SCM_CAR(args);
                SCM mesg  = SCM_CADR(args);
                SCM cargs = SCM_CADDR(args);
#if 1
                /* FIXME: still wrong-type-arg error.. */
                scm_display_backtrace(stack, scm_current_error_port(),
                                      SCM_UNDEFINED, SCM_UNDEFINED);
#endif
                scm_newline(scm_current_error_port());
                scm_display_error(stack, scm_current_error_port(),
                                  subr, mesg, cargs, SCM_EOL);

                return SCM_BOOL_F;
        }
        else
        {
                scm_puts("E991: uncaught throw.",scm_current_error_port());
        }
        return SCM_BOOL_T;

}

======================================================================

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Re: trouble with scm_display_backtrace in guile 1.8.3

[Ludovic Courtès]

Hi,

(I must confess I'd be more comfortable with the same piece of code in
Scheme...  Generally, I find it more convenient to have the boot code as
a Guile script which then loads all the relevant pieces of C code.
Scheme code is also less likely to break with future Guile versions.)

"René Köcher" <shirk87@googlemail.com> writes:

>                 SCM stack = scm_fluid_ref(
>                             SCM_VARIABLE_REF(scm_the_last_stack_fluid_var));
>                 SCM subr  = SCM_CAR(args);
>                 SCM mesg  = SCM_CADR(args);
>                 SCM cargs = SCM_CADDR(args);
> #if 1
>                 /* FIXME: still wrong-type-arg error.. */
>                 scm_display_backtrace(stack, scm_current_error_port(),
>                                       SCM_UNDEFINED, SCM_UNDEFINED);

Presumably STACK is `#f' here, can you confirm it (e.g., by
`scm_write'ing it)?  If so, then this means that `SCM_DEBUG_P' is
somehow not taken into account.

In theory, what you propose should work:

  guile> (define (foo x)
           (catch #t
             (lambda () (error "sdf"))
             (lambda args (fluid-ref the-last-stack))))
  guile> (foo 2)
  #<stack 8050fc0:b7a8dbf0>

As you can see, the error handler gets to see a valid stack when looking
at THE-LAST-STACK.

Thanks,
Ludovic.

Re: trouble with scm_display_backtrace in guile 1.8.3

[RenéKöcher]

Ludovic Courtès <ludo <at> gnu.org> writes:

> 
> Hi,
> 
> (I must confess I'd be more comfortable with the same piece of code in
> Scheme...  Generally, I find it more convenient to have the boot code as
> a Guile script which then loads all the relevant pieces of C code.
> Scheme code is also less likely to break with future Guile versions.)

I agree with you on this but I'm trying to integrate guile within the vim editor
and a extern scheme bootup file just won't fit in 
(neither does embedded scheme source..).

> 
> Presumably STACK is `#f' here, can you confirm it (e.g., by
> `scm_write'ing it)?  If so, then this means that `SCM_DEBUG_P' is
> somehow not taken into account.
Seems that this _was_ the case but I got backtraces working now. 

Sadly I'm not really sure about the 'how' and 'why'..
my ports partition crashed yesterday and so I had to reinstall 
guile and allother macports packages and now my backtraces work
as expected... *weird*
Ϟ
But thanks anyway,

Shirk