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Re: IDLVM and retall [message #49993 is a reply to message #49992]

Fri, 08 September 2006 09:30

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Fri, 08 Sep 2006 09:42:21 -0600, R.G. Stockwell wrote:

>
> "Ben Tupper" <btupper@bigelow.org> wrote in message
> news:4mdendF5h4mvU1@individual.net...
> ...
>> At risk of exposing my arrested development, I harken back to exchange I
>> witnessed between David and Martin Schultz eons ago. I can't remember if
>> it was on the newsgroup or "off-line". But I do remember clearly that
>> Martin and David leaned toward a FUNCTION event handling method rather
>> than a PROcedure - the function event handling method returned 0/1 for
>> fail/success. If I remember rightly, the decision was driven by the
>> messaging aspect of events (or pseudo-events) and that functions, if
>> nothing else, pass messages by default.
>>
>> Would that suffice to resolve the issue?
> ...
>> Cheers,
>> Ben
>
> I was about to suggest the same thing. I have not needed to
> do such a thing in IDL, but in creating very large applications
> in Labview I always had this type of behaviour.
> Every module had an "error input" structure, and if there was
> an error, it just passed through (skipped) the module passing on the error,
> and filling return values with defaults (like NAN or something appropriate).
> One could append the whole routine call tree i guess too.
> The errors were handled at a much higher level.
>
> I have in mind something like the following:
>
> function MyClass::f1, ev, errstruct
> if n_params() ne 2 then message:"developer error: must pass errstruct"
> if (errstruct.set eq FALSE) then begin
> ; no error passed in so perform this function
> result = do_calc(errstruct)
> endif else begin
> ; pass through errors and create default values.
> result = NULL
> endelse
> return, result
> end
>
> pro MyClass::p1, ev, errstruct
> if n_params() ne 2 then message:"developer error: must pass errstruct"
> if (errstruct.set eq FALSE) then begin
> ; no error passed in so do this routine
> do_stuff, ev,errstruct
> endif
> end
>
> function MyClass::f2,ev, errstruct
> OK = self->f1(ev, errstruct) ; error occurs
> result = do_another_calc(ev,errstruct) ; not executed, error passed
> result2 = do_yet_another_calc(result,errstruct); not executed, error
> passed
> result3 = do_yet_another_calc(result2,errstruct); not executed, error
> passed
> result4 = do_yet_another_calc(result3,errstruct); not executed, error
> passed
> return, result4
> end
>
> Coming out of f2 is the errstruct with a message such as:
> "error divide by 1 occurred in myclass f1 function do_calc()"
>
>
> It is a lot of work to retrofit a code base, but it would be easy
> enough to implement when starting out.
> Labview had the very nice feature of easily being able to demand that
> errstruct always be passed (with a dataflow scheme you can do that).

This is so much work that I would probably abandon a consistent error
framework just to avoid it ;). I have many hundreds of individual
methods, and might need to signal an error from any one of them. With my
technique and some care to make changes to instance data "atomic", i.e.
(quasi-)guaranteed either to fail entirely, or succeed completely,
handling errors becomes so much simpler.

JD

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[Message index]

		Re: IDLVM and retall By: JD Smith on Fri, 08 September 2006 09:35
		Re: IDLVM and retall By: JD Smith on Fri, 08 September 2006 09:30
		Re: IDLVM and retall By: JD Smith on Fri, 08 September 2006 09:26
		Re: IDLVM and retall By: JD Smith on Fri, 08 September 2006 09:12
		Re: IDLVM and retall By: news.qwest.net on Fri, 08 September 2006 09:10
		Re: IDLVM and retall By: btt on Fri, 08 September 2006 09:02
		Re: IDLVM and retall By: news.qwest.net on Fri, 08 September 2006 08:42
		Re: IDLVM and retall By: David Fanning on Fri, 08 September 2006 08:28
		Re: IDLVM and retall By: btt on Fri, 08 September 2006 07:57
		Re: IDLVM and retall By: David Fanning on Thu, 07 September 2006 21:00
		Re: IDLVM and retall By: JD Smith on Thu, 07 September 2006 15:57
		Re: IDLVM and retall By: David Fanning on Thu, 07 September 2006 12:14
		Re: IDLVM and retall By: JD Smith on Thu, 07 September 2006 11:54
		Re: IDLVM and retall By: David Fanning on Thu, 07 September 2006 06:52
		Re: IDLVM and retall By: JD Smith on Thu, 07 September 2006 01:57
		Re: IDLVM and retall By: JD Smith on Wed, 06 September 2006 23:21
		Re: IDLVM and retall By: Foldy Lajos on Wed, 06 September 2006 12:30
		Re: IDLVM and retall By: JD Smith on Wed, 06 September 2006 11:53
		Re: IDLVM and retall By: Foldy Lajos on Tue, 05 September 2006 08:31
		Re: IDLVM and retall By: David Fanning on Fri, 08 September 2006 09:48

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