GNU bug report logs - #14922
guard expression doesn't catch everything

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Mark H Weaver <mhw <at> netris.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#14922: closed (guard expression doesn't catch everything)
Date: Mon, 18 Nov 2013 06:18:02 +0000

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Your message dated Mon, 18 Nov 2013 01:16:58 -0500
with message-id <87y54m5j51.fsf <at> netris.org>
and subject line Re: Improving R6RS exception handling in Guile
has caused the debbugs.gnu.org bug report #14922,
regarding guard expression doesn't catch everything
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


-- 
14922: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=14922
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From: Göran Weinholt <goran <at> weinholt.se>
To: bug-guile <at> gnu.org
Subject: guard expression doesn't catch everything
Date: Sun, 21 Jul 2013 11:29:03 +0200

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Hello schemers,

the guard expression from (rnrs) would be a lot more useful if it
managed to catch all exceptions. As it is now, some errors will bypass
the guard:

scheme@(guile-user)> (import (rnrs))
scheme@(guile-user)> (guard (exn (else #f)) (fx+ #f #f))
$1 = #f
scheme@(guile-user)> (guard (exn (else #f)) (fx+))
;;; <stdin>:3:0: warning: possibly wrong number of arguments to `fx+'
rnrs/arithmetic/fixnums.scm:153:2: In procedure fx+:
rnrs/arithmetic/fixnums.scm:153:2: Wrong number of arguments to #<procedure fx+ (fx1 fx2)>

The background is that I'm working on a program that intentionally calls
procedures with bad arguments, and it needs to determine if the
procedure accepted the arguments or not. Ideally the object raised would
be a proper and correct R6RS condition object, but I suspect that most
of the existing Guile code doesn't raise conditions like that. I think
it would be a step forward if guard at least caught the exception, even
if the condition object might not be very useful.

Tested with Guile 2.0.9.40-824b-dirty.

Regards,

-- 
Göran Weinholt <goran <at> weinholt.se>
"Bring me back // to a story left untold // so we can write the ending."
 -- Aly & Fila feat. Jwaydan - We Control The Sunlight

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From: Mark H Weaver <mhw <at> netris.org>
To: Göran Weinholt <goran <at> weinholt.se>
Cc: 14922-done <at> debbugs.gnu.org, guile-devel <at> gnu.org
Subject: Re: Improving R6RS exception handling in Guile
Date: Mon, 18 Nov 2013 01:16:58 -0500

Sorry for the long delay on this.

Göran Weinholt <goran <at> weinholt.se> writes:

> Mark H Weaver <mhw <at> netris.org> writes:
>
>> Hello all,
>>
>> I've cooked up a patch to help improve R6RS exception handling in Guile.
>>
>> As noted by Göran Weinholt in <http://bugs.gnu.org/14922>, the R6RS
>> exception handlers in Guile are currently unable to catch native Guile
>> exceptions.  To fix this, the basic approach of this patch is to convert
>> native Guile exceptions into R6RS conditions within the R6RS exception
>> handlers.
> [...]
>> I'd be grateful for any feedback.
>
> I think it's the right approach to take. I've tested the patch a little
> and it's an improvement over the current state of affairs.

I went ahead and pushed this patch to stable-2.0.  We can work on
incrementally improving it from there.

I'm closing this bug <http://bugs.gnu.org/14922>.

     Thanks!
       Mark

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