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Re: Add nested-function support in a language the based on a stack-machine

From	bartc <bc@freeuk.com>
Newsgroups	comp.compilers
Subject	Re: Add nested-function support in a language the based on a stack-machine
Date	2018-03-06 19:02 +0000
Organization	Compilers Central
Message-ID	<18-03-030@comp.compilers> (permalink)
References	(6 earlier) <18-02-032@comp.compilers> <18-02-034@comp.compilers> <18-03-002@comp.compilers> <18-03-012@comp.compilers> <18-03-020@comp.compilers>

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On 05/03/2018 19:39, George Neuner wrote:
> On Fri, 02 Mar 2018 09:30:42 GMT, anton@mips.complang.tuwien.ac.at
> (Anton Ertl) wrote:

>> Wrong.  Consider the following nesting of functions:
>>
>> A
>> B
>>   C
>> D
>>
>> With a display, in C you have built up a display pointing to the
>> frames of C, B, and A.  When performing a call from C to D, you throw
>> that away and replace it with a display pointing to just the frame of
>> D.  When returning from D, you have to restore the old display.
>
> No.  D and A are at the same lexical level.  On entry, D will replace
> A's entry in the display, and will restore A's entry on exit.
>
> The scope rules say D can't see or call B or C.

What scope rules? As I don't think this is for a specific language.

Even in C, some versions of which have nested functions, it is possible
to set up a function pointer to C(), which can later be called from D()
without first calling A().

And in my own language, it is possible for code in D() to directly call
A.B.C() without entering A.

Although in this one, C() can't access any stack-allocated data of B or
A; partly for this reason (data may not be undefined if called from
outside), and also because it would be fiddly to do anyway, even if
called from B() and A(), as the thread demonstrates.

(C() can access static data of A() and B(), also types, named constants,
enums, and other local functions, so it can still be worthwhile having
local functions with such a restriction.)

--
bartc
[The discussion so far has mostly been about Algol/Pascal style
languages where you can't peek into blocks and contexts go away when a
routine returns so there are no closures.  I agree that if you relax
those rules, life gets more complicated.

Hypothetical question: Algol60 call by name was a mistake.  They
intended an elegant definition of call by reference and didn't realize
until Jensen's device what they'd done.  If they'd done what they
intended and we didn't have to invent thunks, how would programming
languages be different? -John]

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Add nested-function support in a language the based on a stack-machine dror.openu@gmail.com - 2018-02-12 11:25 -0800
  Re: Add nested-function support in a language the based on a stack-machine dror.openu@gmail.com - 2018-02-12 14:16 -0800
    Re: Add nested-function support in a language the based on a stack-machine Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2018-02-13 12:10 +0100
  Re: Add nested-function support in a language the based on a stack-machine Louis Krupp <lkrupp@nospam.pssw.com.invalid> - 2018-02-13 00:42 -0700
    Re: Add nested-function support in a language the based on a stack-machine Kaz Kylheku <217-679-0842@kylheku.com> - 2018-02-14 00:59 +0000
      Re: Add nested-function support in a language the based on a stack-machine George Neuner <gneuner2@comcast.net> - 2018-02-13 22:04 -0500
        Re: Add nested-function support in a language the based on a stack-machine Kaz Kylheku <217-679-0842@kylheku.com> - 2018-02-14 18:06 +0000
          Re: Add nested-function support in a language the based on a stack-machine George Neuner <gneuner2@comcast.net> - 2018-02-15 11:41 -0500
            Re: Add nested-function support in a language the based on a stack-machine Kaz Kylheku <217-679-0842@kylheku.com> - 2018-02-17 16:13 +0000
              Re: Add nested-function support in a language the based on a stack-machine anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2018-02-17 16:39 +0000
                Re: Add nested-function support in a language the based on a stack-machine George Neuner <gneuner2@comcast.net> - 2018-03-01 13:48 -0500
                Re: Add nested-function support in a language the based on a stack-machine Kaz Kylheku <217-679-0842@kylheku.com> - 2018-03-01 19:26 +0000
                Re: Add nested-function support in a language the based on a stack-machine Kaz Kylheku <217-679-0842@kylheku.com> - 2018-03-02 00:38 +0000
                Re: Add nested-function support in a language the based on a stack-machine George Neuner <gneuner2@comcast.net> - 2018-03-02 02:48 -0500
                Re: Add nested-function support in a language the based on a stack-machine rpw3@rpw3.org (Rob Warnock) - 2018-03-03 16:00 +0000
                Re: Add nested-function support in a language the based on a stack-machine anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2018-03-02 09:30 +0000
                Re: Add nested-function support in a language the based on a stack-machine anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2018-03-05 15:01 +0000
                Re: Add nested-function support in a language the based on a stack-machine George Neuner <gneuner2@comcast.net> - 2018-03-05 15:51 -0500
                Re: Add nested-function support in a language the based on a stack-machine George Neuner <gneuner2@comcast.net> - 2018-03-05 14:39 -0500
                Re: Add nested-function support in a language the based on a stack-machine John Levine <johnl@taugh.com> - 2018-03-06 04:31 +0000
                Re: Add nested-function support in a language the based on a stack-machine Kaz Kylheku <217-679-0842@kylheku.com> - 2018-03-06 18:17 +0000
                Re: Add nested-function support in a language the based on a stack-machine Kaz Kylheku <157-073-9834@kylheku.com> - 2018-03-11 03:19 +0000
                Re: Add nested-function support in a language the based on a stack-machine Tomasz Kowaltowski <tk@ic.unicamp.br> - 2018-03-06 12:10 -0300
                Re: Add nested-function support in a language the based on a stack-machine bartc <bc@freeuk.com> - 2018-03-06 19:02 +0000
                Re: Add nested-function support in a language the based on a stack-machine antispam@math.uni.wroc.pl - 2018-04-29 16:29 +0000
              Re: Add nested-function support in a language the based on a stack-machine George Neuner <gneuner2@comcast.net> - 2018-03-01 13:49 -0500
    Re: Add nested-function support in a language the based on a stack-machine George Neuner <gneuner2@comcast.net> - 2018-02-13 22:37 -0500
  Re: Add nested-function support in a language the based on a stack-machine George Neuner <gneuner2@comcast.net> - 2018-02-13 23:27 -0500
  Re: Add nested-function support in a language the based on a stack-machine Shoefoot <shoefoot@gmail.com> - 2018-02-14 12:27 -0800

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