Re: More on Boolean Shortcircuiting

Newsgroups	comp.lang.forth
From	Albert van der Horst <albert@spenarnc.xs4all.nl>
Subject	Re: More on Boolean Shortcircuiting
Date	2012-05-31 18:38 +0000
Message-ID	<m4wh3w.dn8@spenarnc.xs4all.nl> (permalink)
Organization	Dutch Forth Workshop
References	<jpq8c0$30h$1@dont-email.me> <jq58ml$25h$1@dont-email.me> <m4vyf5.eg3@spenarnc.xs4all.nl> <jq822d$4a8$1@dont-email.me>

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In article <jq822d$4a8$1@dont-email.me>,
Arnold Doray  <invalid@invalid.com> wrote:
>On Thu, 31 May 2012 11:54:41 +0000, Albert van der Horst wrote:
>
>>
>> Have you experience using Forth's CATCH THROW? Probably not, because the
>> above is patently untrue.
>>
>> I have experience and this is what I would say:
>>
>> "
>> One would be hard pressed to come up with a realistic example where the
>> stack after a CATCH is disturbed beyond the data passed to the word that
>> is executed.
>> "
>>
>> What do you have in mind?
>> Do you think CATCH is used to recover from program errors where you
>> accidentally underflow the data stack?
>>
>
>
>I have just come from the Java world, where deep exceptions (those thrown
>well up in the calling hierarchy) are the norm. Java deals with this by
>allowing the programmer to trace the exception's propagation through the
>call hierarchy, so you can see immediately what went wrong. Deep
>exceptions are a byproduct of modular programming / programming with
>libraries.
>
>The "problem" I see with THROW's behaviour is that just *before* an
>exception is thrown, the stack could have been:
>
>A) Added to -- in which case THROW does a useful thing by dropping all
>the stuff generated by the XT that CATCH executed.
>
>B) Depleted -- in which you get junk on the stack. You have to manually
>clean these or drop the entire stack.
>
>C) Muddled  (ie, items added to / removed ) -- in which case you are
>likely to just drop the entire stack.
>
>I guess in B and C, you would just drop the entire stack? IMHO, B and C
>are likely to occur in larger bodies of code.
>
>And A would only happen when you knew exactly where those exceptions
>would be thrown (ie, code you wrote yourself, not locked away in a
>library). Is this the right way of seeing it?

Yes. An example may clarify it further:

Let us imagine a situation where MY-THING has the stack-profile
( x1,x2,x3 -- y1 )

what we really would like to have upon a 17 THROW
 1 2 3   a b c ' MY-THING CATCH is just
 1 2 3 17                  1]
i.e. restoration of the stack and notification of which exception.
However CATCH doesn't know or care what the stack-diagram of MY-THING is.
So the stack pointer is restored, maybe indeed revealing garbage:
1 2 3 a z   \ Throw at this point of 17
         ^
1 2 3 a z garbage-item  17
                       ^
                       restored stackpointer.
So that is what is seen at the point of the catch.

So: `` 1 2 3 '' is never touched, not even in case of a throw.
And the `` a z garbage-item '' doesn't contain information and should
be disposed of. Manually that is, because CATCH doesn't know.

(One *could* use it, this is Forth after all, but that would be really
bad practice.)

I find exceptions in Forth easy because you're not tempted to let them
bubble up to a point where you no longer know what to do with them.

>
>Cheers,
>Arnold


1] And  `` 1 2 3 d 0 '' if it went okay.


--
-- 
Albert van der Horst, UTRECHT,THE NETHERLANDS
Economic growth -- being exponential -- ultimately falters.
albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst

Thread

More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-26 09:39 +0000
  Re: More on Boolean Shortcircuiting Josh Grams <josh@qualdan.com> - 2012-05-26 12:44 +0000
    Re: More on Boolean Shortcircuiting Josh Grams <josh@qualdan.com> - 2012-05-26 12:47 +0000
      Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-26 14:16 +0000
    Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-26 13:48 +0000
      Re: More on Boolean Shortcircuiting Josh Grams <josh@qualdan.com> - 2012-05-27 00:17 +0000
  Re: More on Boolean Shortcircuiting BruceMcF <agila61@netscape.net> - 2012-05-26 08:27 -0700
    Re: More on Boolean Shortcircuiting BruceMcF <agila61@netscape.net> - 2012-05-26 10:25 -0700
      Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-27 10:47 +0000
        Re: More on Boolean Shortcircuiting BruceMcF <agila61@netscape.net> - 2012-05-27 07:00 -0700
          Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-27 17:20 +0000
            Re: More on Boolean Shortcircuiting BruceMcF <agila61@netscape.net> - 2012-05-27 15:03 -0700
  Re: More on Boolean Shortcircuiting "David N. Williams" <williams@umich.edu> - 2012-05-26 17:17 -0400
    Re: More on Boolean Shortcircuiting BruceMcF <agila61@netscape.net> - 2012-05-26 14:49 -0700
    Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-27 10:21 +0000
  Re: More on Boolean Shortcircuiting Josh Grams <josh@qualdan.com> - 2012-05-28 14:24 +0000
    Re: More on Boolean Shortcircuiting BruceMcF <agila61@netscape.net> - 2012-05-28 10:27 -0700
      Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-29 09:18 +0000
    Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-28 12:41 -0500
      Re: More on Boolean Shortcircuiting "Elizabeth D. Rather" <erather@forth.com> - 2012-05-28 07:55 -1000
    Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-29 11:34 +0000
    Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-29 13:53 +0000
      Re: More on Boolean Shortcircuiting Alex McDonald <blog@rivadpm.com> - 2012-05-29 07:02 -0700
        Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-30 01:45 +0000
          Re: More on Boolean Shortcircuiting BruceMcF <agila61@netscape.net> - 2012-05-29 20:02 -0700
            Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-30 04:27 +0000
              Re: More on Boolean Shortcircuiting Alex McDonald <blog@rivadpm.com> - 2012-05-30 02:09 -0700
                Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-30 11:07 +0000
                Re: More on Boolean Shortcircuiting Alex McDonald <blog@rivadpm.com> - 2012-05-30 04:38 -0700
                Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-30 06:46 -0500
                Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-30 13:52 +0000
                Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-30 09:02 -0500
                Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-30 14:13 +0000
                Re: More on Boolean Shortcircuiting Alex McDonald <blog@rivadpm.com> - 2012-05-30 07:41 -0700
                Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-30 11:46 -0500
                Re: More on Boolean Shortcircuiting BruceMcF <agila61@netscape.net> - 2012-05-31 09:18 -0700
                Re: More on Boolean Shortcircuiting Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-05-31 11:54 +0000
                Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-31 15:17 +0000
                Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-31 11:17 -0500
                Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-31 17:40 +0000
                Re: More on Boolean Shortcircuiting "Elizabeth D. Rather" <erather@forth.com> - 2012-05-31 08:43 -1000
                Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-06-01 02:56 +0000
                Re: More on Boolean Shortcircuiting anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-06-01 09:49 +0000
                Re: More on Boolean Shortcircuiting "Elizabeth D. Rather" <erather@forth.com> - 2012-06-01 09:18 -1000
                Re: More on Boolean Shortcircuiting Josh Grams <josh@qualdan.com> - 2012-05-31 16:45 +0000
                Re: More on Boolean Shortcircuiting BruceMcF <agila61@netscape.net> - 2012-05-31 09:58 -0700
                Re: More on Boolean Shortcircuiting Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-05-31 18:38 +0000
                Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-06-01 03:09 +0000
                Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-06-01 02:44 -0500
                Re: More on Boolean Shortcircuiting Mark Wills <markrobertwills@yahoo.co.uk> - 2012-06-01 04:57 -0700
                Re: More on Boolean Shortcircuiting anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-06-01 12:45 +0000
                Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-06-01 08:45 -0500
                Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-06-01 15:18 +0000
              Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-30 06:39 -0500
      Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-29 09:52 -0500
        Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-30 01:48 +0000
          Re: More on Boolean Shortcircuiting Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2012-05-30 07:55 +0100
          Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-30 02:56 -0500
            Re: More on Boolean Shortcircuiting Arnold Doray <invalid@invalid.com> - 2012-05-30 11:31 +0000
              Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-30 06:53 -0500
                Re: More on Boolean Shortcircuiting Alex McDonald <blog@rivadpm.com> - 2012-05-30 05:04 -0700
                Re: More on Boolean Shortcircuiting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-30 09:03 -0500
      Re: More on Boolean Shortcircuiting Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2012-05-29 17:49 +0100
        Re: More on Boolean Shortcircuiting Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2012-05-29 19:06 +0100
      Re: More on Boolean Shortcircuiting Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-05-29 20:25 +0000

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