Re: saving and restoring the error stack trace

[Marco Maggi]

"Neil Jerram" wrote:
> [...] please let me know your thoughts on it -
> most importantly, of course, whether it answers your
> question!

Making the stack with this:

  s_error_stack = scm_make_stack(SCM_BOOL_T, SCM_EOL);

and using the function (scm_t = SCM):

void
rethrow_error_with_stack (scm_t s_error_stack,
                          scm_t s_error_key,
                          scm_t s_error_args,
                          const char * procname)
{
  scm_t         s_port, s_string, s_stack;
  size_t        len;

  s_stack = scm_make_stack(SCM_BOOL_T, SCM_EOL);
  len =
    scm_to_uint(scm_stack_length(s_error_stack)) -
    scm_to_uint(scm_stack_length(s_stack)) - 1;

  s_port = scm_open_output_string();
  {
    scm_t       s_message =
scm_list_ref(s_error_args,scm_from_uint(1));
    scm_t       s_args    =
scm_list_ref(s_error_args,scm_from_uint(2));

    scm_simple_format(s_port, s_message,
                      (scm_is_eq(SCM_BOOL_F, s_args)? SCM_EOL : s_args));
    scm_newline(s_port);
    scm_display_backtrace(s_error_stack, s_port,
                          scm_from_uint(len), SCM_UNDEFINED);
    s_string = scm_get_output_string(s_port);
  }
  scm_close_output_port(s_port);
  scm_error_scm(s_error_key, scm_from_locale_string(procname),
                s_string, SCM_BOOL_F,
                scm_list_ref(s_error_args, scm_from_uint(3)));
}

I have error messages like:

Backtrace:
In unknown file:
   ?: 0* [dotest "gsl-ode-error-2.4" #<procedure #f ()> ...]
   ?: 1  (let* () (let* (# #) (let* # #)))
   ...
   ?: 2  (begin (display name) (if (thunk? setup) (setup)) ...)
   ?: 3* (let (# # # ...) (set-current-input-port saved-in) ...)
   ?: 4* (if catch-error (catch #t thunk (lambda (key .
args) key)) (thunk))
   ?: 5  [#<procedure #f ()>]
   ...
   ?: 6  (let* ((result (quote ()))) (if debugging
(newline)) ...)
   ?: 7* [gsl-ode-evolve #<universal GSL SMOB 404697f8>
#:initial-indep-value ...]
   ?: 8  (let-keywords args #f ...)
   ...
   ?: 9  [gsl-p-ode-evolve #<universal GSL SMOB 404697f8>
0.0 ...]

<unnamed port>: In procedure gsl-ode-evolve in expression
(gsl-p-ode-evolve ode initial-indep-value ...):
<unnamed port>: my error message 1 and 2
In unknown file:
   ?: 10* [#<procedure #f (t y)> 0.0 #,(gsl-vector-real 1 2.0)]
   ?: 11* [gsl-ode-invoke-fun 0.0 #,(gsl-vector-real 1 2.0) ...]
   ?: 12  (let* ((o (func t #))) (if (gsl? o) (slot-ref o
(quote v)) ...))
   ?: 13* [#<procedure #f (t y)> 0.0 #,(gvr 1  2.0)]
   ?: 14  [throwing-error]
    ...
   ?: 15  [scm-error my-own-error "sub-throwing-error" ...]

which is not perfect but seems good enough for me.

I am a little annoyed that I have to use a port to
build the backtrace string, and that the args content
is not explicitly documented (that is, I was not
able to find it) even if its content is well defined
in 'scm_error_scm()':

  scm_ithrow (key,
        scm_list_4 (subr, message, args, data), 1);


--
Marco Maggi

"They say jump!, you say how high?"
Rage Against the Machine - "Bullet in the Head"