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

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George Neuner <gneuner2@comcast.net> wrote:
> On Fri, 02 Mar 2018 09:30:42 GMT, anton@mips.complang.tuwien.ac.at
> (Anton Ertl) wrote:
>
> >George Neuner <gneuner2@comcast.net> writes:
> >>On Sat, 17 Feb 2018 16:39:04 GMT, anton@mips.complang.tuwien.ac.at
> >>(Anton Ertl) wrote:
> >>
> >>>Kaz Kylheku <217-679-0842@kylheku.com> writes:
> >>>>On 2018-02-15, George Neuner <gneuner2@comcast.net> wrote:
> >>>>> No worries.  IME, displays don't get much respect from modern
> >>>>> textbooks - they are mentioned mostly in passing.
> >>>>
> >>>>This is probably because of
> >>>
> >>>This is because displays were found to be more costly for Algol-like
> >>>languages
> >>
> >>More costly than what?
> >
> >Static link chains.
> >
> >>> IIRC the additional cost is in updating the display on calls
> >>>and returns.
> >>
> >>Which is no different from the overhead to maintain static links
> >
> >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.  If it calls A, then A
> replaces it at the same lexical level.  When A returns, D's link is
> restored.

You assume no procedure parameters (boring case).  With procedure
parameters C can pass itself (or B or other procedure at the
same lexical level) to D and D can call it.  So dynamic chain
can be:

A B C D C

and innermost C needs to see A variables in its display.
IIUC resolving this required copies that make display
management O(n) (n being depth of static chain).

> No problem.  And no need to preserve the whole display.
>
> >If you don't maintain a static link chain, you have to save the
> >complete display of C on the call and restore it on return.
>
> No you don't.
>
>
> >Note that D may itself call functions that need more display, so you don't get
> >away with just saving and restoring the first slot of the display.
> >IIRC this was the variant looked at in the paper that concluded that
> >displays are more costly.
>
> That is simply wrong unless you change the whole semantics.
>
> As long as call sites are restricted to being within the definition
> scope of the called function [as is true in Pascal],

Pascal without procedural parameters.

--
                              Waldek Hebisch

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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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