Re: reporting 'system-error informatively

[Marius Vollmer <mvo@zagadka.ping.de>]

prj@po.cwru.edu (Paul Jarc) writes:

> If I catch 'system-error and display an error message, I'd like to
> include the arguments of the procedure that failed along with the
> procedure name and errno string.  Is there a way to get the arguments
> programmatically, other than by parsing the output of (backtrace)?

The arguments are passed among the arguments received by the handler.
You can do something like

    (define (call-with-error-catching thunk)
      (let ((the-last-stack #f)
            (stack-saved? #f))

        (define (handle-error key args)
          (let ((text (call-with-output-string
                       (lambda (cep)
                         (if the-last-stack
                             (display-backtrace the-last-stack cep)
                             (display "no backtrace available.\n" cep))
                         (apply display-error the-last-stack cep args)))))
            ;;; you probably need to do something else with the text.
            (gtk-show-error text)
            #f))

        (define (save-stack)
          (cond (stack-saved?)
                ((not (memq 'debug (debug-options-interface)))
                 (set! the-last-stack #f)
                 (set! stack-saved? #t))
                (else
                 (set! the-last-stack (make-stack #t lazy-dispatch 4))
                 (set! stack-saved? #t))))

        (define (lazy-dispatch key . args)
          (save-stack)
          (apply throw key args))

        (start-stack #t
                     (catch #t
                            (lambda ()
                              (lazy-catch #t
                                          thunk
                                          lazy-dispatch))
                            (lambda (key . args)
                              (if (= (length args) 4)
                                  (handle-error key args)
                                  (apply throw key args)))))))

which is probably way too complicated.  This is a weak spot of Guile,
I'm afraid.

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