Hi Vaidotas,
Thanks for the feedback; great example… I’ll investigate. I plan to revisit exceptions later and let you know :)
Thanks again,
Jaromir

From: Vaidotas Didžbalis<mailto:vaidasd at gmail.com>
Sent: Monday, March 7, 2022 17:15
To: The general-purpose Squeak developers list<mailto:squeak-dev at lists.squeakfoundation.org>
Subject: Re: [squeak-dev] Slightly incorrect implementation of #resignalAs: ??

Hello Jaromir, all,
Change affects re-signaling exceptions of the same kind, line below falls into endless loop in Trunk. It works differently in Squeak 5.3 or 4.2:
[Error new signal: 'some error'] on: Error do: [:e | e resignalAs: (DomainError new messageText: 'some domain error')].
regards,
Vaidotas


On Fri, Feb 4, 2022 at 4:15 PM <mail at jaromir.net<mailto:mail at jaromir.net>> wrote:
Hi Jakob, all,

I give up this experiment of mine; I've realized using #restartWithNewReceiver is tricky and very non-OOP: replacing a receiver with an object of a different type introduces unexpected consequences and checking the type of the replacement object is so not-object-oriented; the best I could come up with is:

resignalAs: replacementException
        "Signal an alternative exception in place of the receiver."

        (replacementException isKindOf: Exception class) ifTrue: [^self resignalAs: replacementException new].
        (replacementException isKindOf: Exception) ifFalse: [^self error: 'wrong replacementException type'].
        signalContext restartWithNewReceiver: replacementException

This would be a clean implementation of ANSI's #resignalAs with a nice stack when debugging; compare with the confusing stack currently produced for e.g.:

        [self error] on: Error do: [:ex | ex resignalAs: Warning new]

Besides, the current implementation allows nonsense like this evaluate silently:

        [self error] on: Error do: [:ex | ex resignalAs: Semaphore new]

but it probably doesn't do much harm and doesn't justify changing the current simple implementation.

So unless someone sees any value in the above implementation I won't clutter the Inbox :)

Thanks.

best,
Jaromir
^[^
  --
Sent from Squeak Inbox Talk

On 2022-01-29T21:43:17+01:00, mail at jaromir.net<mailto:mail at jaromir.net> wrote:

> Hi Jakob,
>       a correction:
>
> > > As so often, the breaking of applications that relied on the
> > > non-standard behavior may be an obstacle.
> > Yes indeed, that's a pain... theoretically as a workaround a class method could be added to create an instance and send it the instance side #resignalAs.
>
> Sorry, ignore me please, no class method indeed, but something like this:
>
> resignalAs: replacementException
>       "Abort an exception handler and signal an alternative exception in place of the receiver.
>        Allow an exception class as replacementException as an extension of ANSI specification:
>               [1/0] on: Error do: [:ex | ex resignalAs: Warning new]    <--- ANSI compliant
>               [1/0] on: Error do: [:ex | ex resignalAs: Warning]           <--- Squeak extension"
>
>       (replacementException isKindOf: Exception class) ifTrue: [
>               self resignalAs: replacementException new].
>       signalContext restartWithNewReceiver: replacementException
>
> a bit ugly... Or keep it simple, no extension?
>
> resignalAs: replacementException
>       "Abort an exception handler and signal an alternative exception in place of the receiver."
>
>       signalContext restartWithNewReceiver: replacementException
>
> best,
> ~~~
> ^[^    Jaromir
>
> Sent from Squeak Inbox Talk
>
> On 2022-01-29T20:18:40+01:00, mail at jaromir.net<http://jaromir.net> wrote:
>
> > Hi Jakob,
> >
> > thanks for your reply.
> >
> > The proposed change is not supposed to change the semantics of resignalAs in any way (except limiting the argument to an exception instance, not a class).
> >
> > We already have 3 resignalAs tests - is this ok? Pharo/Cuis are behind Squeak and as for VW I'm not familiar with their testing just yet.
> >
> > The tests are green; well, after fixing my own contribution from last year (doubleOuterResignalAsTest) where I erroneously used a class as #resignalAs's argument - what a shame :) I'll definitely send a fix of this test to the Inbox.
> >
> > > As so often, the breaking of applications that relied on the
> > > non-standard behavior may be an obstacle.
> > Yes indeed, that's a pain... theoretically as a workaround a class method could be added to create an instance and send it the instance side #resignalAs. However looking at its senders this method doesn't feel like frequently used :) (VA didn't even bother to implement it, at least in the version I have)
> >
> > best,
> > ~~~
> > ^[^    Jaromir
> >
> > Sent from Squeak Inbox Talk
> >
> > On 2022-01-29T18:53:24+01:00, jakres+squeak at gmail.com<http://gmail.com> wrote:
> >
> > > Hi Jaromir,
> > >
> > > We should start with a test case. I agree with your interpretation of
> > > the standard and see no harm in an inbox submission.
> > > Is there some ANSI Smalltalk test suite out there that could be shared
> > > between the dialects?
> > >
> > > As so often, the breaking of applications that relied on the
> > > non-standard behavior may be an obstacle.
> > >
> > > Kind regards,
> > > Jakob
> > >
> > > Am Sa., 29. Jan. 2022 um 17:43 Uhr schrieb <mail at jaromir.net<http://jaromir.net>>:
> > > >
> > > > Hi all,
> > > >
> > > > I think Squeak's implementation of #resignalAs: is not following the ANSI specification precisely. Currently it reads:
> > > >
> > > > resignalAs: replacementException
> > > >
> > > >         signalContext resumeEvaluating: [replacementException signal]
> > > >
> > > > ANSI says:
> > > > "
> > > > The active exception action is aborted and the exception environment *and the evaluation context*
> > > > are restored to the same states that were in effect when the receiver was originally signaled.
> > > > This message (i.e. resignalAs:) causes the replacementException to be treated as if it had been originally
> > > > signaled instead of the receiver.
> > > > "
> > > >
> > > > This is very similar to #retry (or #retryUsing:) specification so I'd suggest the following implementation:
> > > >
> > > > resignalAs: replacementException
> > > >
> > > >         signalContext restartWithNewReceiver: replacementException
> > > >
> > > > The current implementation leads to building the new resignaled contexts on top of the previous signal contexts (and the resignalAs context itself) instead of simply *restarting* the previous signal context with the replacement exception as the new receiver. In my opinion the suggested implementation precisely follows the ANSI specification, and is consistent with current #retry and #retryUsing: implementation - compare:
> > > >
> > > > retryUsing: alternativeBlock
> > > >         "Abort an exception handler and evaluate a new block in place of the handler's protected block."
> > > >
> > > >         handlerContext restartWithNewReceiver: alternativeBlock
> > > >
> > > > Other dialects: Pharo and Cuis copied Squeak's but VW implemented resignalAs: to comply with ANSI precisely.
> > > >
> > > > One consideration: the current implementation allows "exception resignalAs: Error", i.e. allows Exception class as an argument but ANSI's version requires "exception resignalAs: Error new". All senders (there are just a few) in the base image seem use "Error new" anyway.
> > > >
> > > > My arguments for are: consistency, readability and less complexity (especially while debugging)
> > > >
> > > > What do you think? Inbox it?
> > > >
> > > > best,
> > > > ~~~
> > > > ^[^    Jaromir
> > > >
> > > > Sent from Squeak Inbox Talk
> > > >
> > >
> > >
> >
> >
>
>

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