[Larceny-users] recursive lists and C-c problems

[Ray Racine]

http://github.com/GreyLensman/rl3/tree/webserver/rl3/env/debug.sls

Here is another example of establishing your own error handler in ERR5RS
(R6RS kinda sorta) Larceny.
I had it bound to my emacs.  When debug was "disabled" the handler prints
the error and leaves you at the top level REPL and not in the debugger.  Its
just a simple example.  Dave's solution actually give a solution for your
specific concern.

There is some other Larceny ERR5RS sorta/kinda R6RS code there as well.
Unfortunately its not system agnostic and a clean build with
compile-stale-libraries requires a Linux box.  Its mostely web oriented.
HTTP, continuation threading, sockets support that works with the R6RS I/O,
SXML, Amazon Cloud client code, a small REST web server, etc...
Unfortunately its not well documented and a bit of mess.  I hope to get back
to it early next year.

Ray

On Mon, Dec 8, 2008 at 4:06 PM, David Rush <kumoyuki at gmail.com> wrote:

> 2008/12/8 Marco Maggi <marco.maggi-ipsu at poste.it>
> > "will at ---" wrote:
> > >Marco Maggi wrote:
> >
> > >> After hitting C-c, I see that the debugger is here
> > >> and I can exit it with "q". And I am left with a prompt?
> > >
> > >Yes.  It isn't a very useful prompt, since nothing is
> > >in scope, but it's a prompt.
> >
> > Nothing is in scope until I issue "(import (rnrs))",
> > then I do what I want with escalated privileges.
>
> As I said earlier, if you're running setuid, you should have
> *thoroughly* debugged your code. Then you will not hit the prompt.
>
> > It would suffice to have a command line switch that
> > makes the process exit whenever an exception is not
> > blocked.
>
> How about installing your own error-handler that just exits the
> program? There's a really simple API for this. You could minimally
> just use the code:
>
>     (error-handler (lambda _ (exit)))
>
> and get your result. Which is not very helpful because is you haven't
> debugged sufficiently that you are still getting errors which
> terminate the program, you generally would like to know what went
> wrong. Hence the following code (which is part of my Larceny standard
> prelude):
>
>    (require 'inspect-cont)
>    (define (batch/last-chance-handler puts)
>     (lambda e
>       (define (display-line s)
>         (puts (with-output-to-string
>                 (lambda() (write s)))))
>
>       (display-line `(lastchance error handler ,e))
>
>       (let* ((error-text
>               (call-with-output-string (lambda (p) (decode-error e p))))
>              (stacktrace (current-continuation-structure))
>              (inspector (make-continuation-inspector stacktrace))
>
>              (summarize-frame
>               (lambda (count inspector . prefix)
>                 (let* ((frame (inspector 'get))
>                        (code  (frame 'code))
>                        (class (code 'class))
>                        (expr  (code 'expression))
>                        (proc  (code 'procedure)))
>                   (display-line
>                    `(frame , at prefix ,class
>                            ,@(case class
>                                ((system-procedure) '())
>                                ((interpreted-primitive) (procedure-name
> proc))
>                                ((interpreted-expression) expr)
>                                ((compiled-procedure) (procedure-name proc))
>                                (else '())))
>                    ))))
>
>              (backtrace
>               (lambda (count inspector)
>                 (let loop ((c (inspector 'clone)))
>                   (let ((f (c 'get)))
>                     (if (f 'same? (inspector 'get))
>                         (summarize-frame 0 c "=> ")
>                         (summarize-frame 0 c "   ")))
>                   (if (c 'down)
>                       (loop c))
>                   )))
>              )
>         (display-line `(decoded error ,error-text))
>         (backtrace 0 inspector)
>         (exit 0)
>         )))
>
>    (define (install-lastchance puts)
>      (error-handler (batch/last-chance-handler puts))
>
> To use this fragment, call:
>
>    (install-lastchance puts-function)
>
> where puts-function takes a string and does something appropriate with it.
>
> david
> --
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>
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