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Re: Is multi-level function return possible?

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On 2014-03-11, Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
> noitalmost <noitalmost@cox.net> writes:
>>Is this a doable thing for a Pascal-like language that is meant to be
>>compiled? I have a multi-level break which works within a procedure, but the
>>return across procedure boundaries seems to add a lot of complications.
>
> Yes, in Pascal you can goto a label that is in a containing procedure
> or function, even across several levels.  That is a very rarely used

I.e. you can jump out of a "downward funarg" closure in that original Pascal,
back to the parent environment, just like in Lisp.

> feature of the language, and Wirth removed it (along with goto) from
> his later languages.

Then Cardelli added lexically scoped symbol macros to Modula-3, not
unlike (symbol-macrolet ...) in the form of the new, improved version
of the WITH statement.

Maybe one day these Pascalites will assemble a complete language that
has everything at the same time.


> The more common feature is to have exceptions that you can throw and
> that can be caught in a function/procedure/method several levels
> further out.
>
> The difference between these languages features is that Pascal's goto
> is statically scoped, whereas exceptions are dynamically scoped.

But if Pascal had upward funargs (closures that can be returned from the scope
in which they are created), then the goto, though lexically scoped, would have
have a test to detect that its target is no longer in the dynamic scope.

I.e. it's not really purely lexical. Resolving the label identifier is lexical,
but the situation is dynamic.

Also, never mind full closures: consider the situation that the function is
simply recursive.

Recursion means there is possibly more than one activation of the environment
which contains the target label of the goto. Which activation is chosen as the
jump target? Does the goto return to the same recursion level in which
the closure was created or does it just find the innermost activation of
that label?

If the closure jsut goes to the innermost block which has the label,
then the target resolution is in fact dynamically scoped, even though
the label is lexical. (Because the target block is not lexically captured
along with the closure, but chosen just from whatever is visible at the
time the goto takes place.)

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Is multi-level function return possible? noitalmost <noitalmost@cox.net> - 2014-03-10 15:46 -0400
  Re: Is multi-level function return possible? Kaz Kylheku <kaz@kylheku.com> - 2014-03-11 05:20 +0000
  Re: Is multi-level function return possible? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-03-11 13:04 +0000
    Re: Is multi-level function return possible? Kaz Kylheku <kaz@kylheku.com> - 2014-03-11 22:15 +0000
      Re: Is multi-level function return possible? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-03-13 17:05 +0000
        Re: Is multi-level function return possible? Bill Findlay <yaldnif.w@blueyonder.co.uk> - 2014-03-14 01:28 +0000
        Re: Is multi-level function return possible? Ivan Godard <ivan@ootbcomp.com> - 2014-03-13 18:32 -0700
          Re: Is multi-level function return possible? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-14 20:27 +0000
      Re: Is multi-level function return possible? George Neuner <gneuner2@comcast.net> - 2014-03-14 02:39 -0400
        Re: Is multi-level function return possible? Kaz Kylheku <kaz@kylheku.com> - 2014-03-14 21:34 +0000
          Re: Is multi-level function return possible? Marco van de Voort <marcov@toad.stack.nl> - 2014-03-14 22:59 +0000
        Re: Is multi-level function return possible? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-03-16 17:19 +0000
          Re: Is multi-level function return possible? Marco van de Voort <marcov@toad.stack.nl> - 2014-03-16 18:39 +0000
          Re: Is multi-level function return possible? Andy Walker <news@cuboid.co.uk> - 2014-03-16 19:45 +0000
            Re: Is multi-level function return possible? Bill Findlay <yaldnif.w@blueyonder.co.uk> - 2014-03-17 16:15 +0000
              Re: Is multi-level function return possible? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-03-18 17:36 +0000
                Re: Is multi-level function return possible? Andy Walker <news@cuboid.co.uk> - 2014-03-21 02:04 +0000
                Re: Is multi-level function return possible? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-21 02:50 +0000
                Re: design of PL/I, was Is multi-level function return possible? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-21 06:43 +0000
                Re: design of PL/I, was Is multi-level function return possible? noitalmost <noitalmost@cox.net> - 2014-03-26 14:16 -0400
                Re: exception catching in PL/I, was Is multi-level function return possible? "Robin Vowels" <robin51@dodo.com.au> - 2014-03-27 21:08 +1100
                Re: Is multi-level function return possible? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-03-24 17:06 +0000
                Re: Is multi-level function return possible? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-24 20:01 +0000
                Re: Is multi-level function return possible? George Neuner <gneuner2@comcast.net> - 2014-03-26 04:00 -0400
                Re: Is multi-level function return possible? Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2014-03-27 01:58 +0100
                Re: Is multi-level function return possible? Stefan Monnier <monnier@iro.umontreal.ca> - 2014-04-07 14:48 -0400
                Re: Is multi-level function return possible? Andy Walker <news@cuboid.co.uk> - 2014-03-26 12:16 +0000
                Re: Is multi-level function return possible? Andy Walker <news@cuboid.co.uk> - 2014-03-26 17:34 +0000
                Re: history of C, was Is multi-level function return possible? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-27 00:05 +0000
      Re: Is multi-level function return possible? Bakul Shah <usenet@bitblocks.com> - 2014-03-15 10:28 -0700
    Re: Is multi-level function return possible? George Neuner <gneuner2@comcast.net> - 2014-03-14 02:44 -0400
      Re: Is multi-level function return possible? Marco van de Voort <marcov@toad.stack.nl> - 2014-03-14 19:38 +0000
      Re: Is multi-level function return possible? Kaz Kylheku <kaz@kylheku.com> - 2014-03-14 21:36 +0000
      Re: Is multi-level function return possible? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-14 21:47 +0000
        Re: Is multi-level function return possible? Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2014-03-15 13:34 +0100
      Re: Is multi-level function return possible? Ian Lance Taylor <ian@airs.com> - 2014-03-14 16:55 -0700
  Re: Is multi-level function return possible? George Neuner <gneuner2@comcast.net> - 2014-03-11 13:56 -0400
    Re: Is multi-level function return possible? federation2005@netzero.com - 2014-03-26 17:39 -0700
      Re: catch and throw, was Is multi-level function return possible? rpw3@rpw3.org (Rob Warnock) - 2014-03-27 04:23 +0000
        Re: catch and throw, was Is multi-level function return possible? Kaz Kylheku <kaz@kylheku.com> - 2014-03-27 05:44 +0000
        Re: catch and throw, was Is multi-level function return possible? Bakul Shah <usenet@bitblocks.com> - 2014-03-26 23:20 -0700
          Re: catch and throw, was Is multi-level function return possible? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-27 19:21 +0000
          Re: exception catching in PL/I "Robin Vowels" <robin51@dodo.com.au> - 2014-03-28 10:50 +1100
            Re: exception catching in PL/I Martin Ward <martin@gkc.org.uk> - 2014-04-16 14:32 +0100
          Re: catch and throw, was Is multi-level function return possible? mac <acolvin@efunct.com> - 2014-03-28 23:08 +0000
            Re: catch and throw, was Is multi-level function return possible? Ivan Godard <ivan@ootbcomp.com> - 2014-03-28 18:24 -0700
              Re: catch and throw, was Is multi-level function return possible? Kaz Kylheku <kaz@kylheku.com> - 2014-03-29 02:47 +0000
                Re: catch and throw, was Is multi-level function return possible? Ivan Godard <ivan@ootbcomp.com> - 2014-03-28 21:32 -0700
              Re: catch and throw, was Is multi-level function return possible? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-29 03:38 +0000
                Re: precise and imprecise, was catch and throw, was Is multi-level function return possible? Ivan Godard <ivan@ootbcomp.com> - 2014-03-28 22:12 -0700
            Re: catch and throw, was Is multi-level function return possible? Kaz Kylheku <kaz@kylheku.com> - 2014-03-29 02:07 +0000
              Re: catch and throw, was Is multi-level function return possible? Alan Bawden <alan@scooby-doo.csail.mit.edu> - 2014-03-29 02:44 -0400
            Re: PL/I exceptions, was catch and throw, was Is multi-level function return possible? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-29 02:40 +0000
              Re: PL/I exceptions "Robin Vowels" <robin51@dodo.com.au> - 2014-03-30 01:58 +1100
      Re: catch and throw, was Is multi-level function return possible? George Neuner <gneuner2@comcast.net> - 2014-03-28 03:52 -0400
  Re: Is multi-level function return possible? Louis Krupp <lkrupp@pssw.com> - 2014-03-11 15:16 -0600
  Re: Is multi-level function return possible? noitalmost <noitalmost@cox.net> - 2014-03-15 12:21 -0400

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