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Re: Quotations revisited

From stephenXXX@mpeforth.com (Stephen Pelc)
Newsgroups comp.lang.forth
Subject Re: Quotations revisited
Message-ID <50040282.189860346@192.168.0.50> (permalink)
References <00808889968435@frunobulax.edu>
Date 2012-07-16 12:01 +0000

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A revised summary, 16 July 2012

Given the increasing popularity of talking about "quotations" and
"closures", it would be useful to have a specification to talk
about.

Andrew provided an implementation of quotations that will only
make sense to people with carnal knowledge of SwiftForth. Bernd
provided an implementation that will only make sense to people
with carnal knowledge of VFX Forth.

I see that that quotations can provide pretty notations at little
cost. On closures I remain unconvinced, but have not seen a Forth
implementation or notation.

I have seen two or three sets of requirements dicussed, but for
those of us who distinguish between hand-waving, source code and
specifications, would an interested party be prepared to specify
what is required? It seems that the interested party is going to
have to be me.

Stephen
P.S. "Go read this in WikiPedia" is inadequate.
P.P.S. "Read the source, Luke" is inadequate.

The following notes on quotations and closures incorporate
material from several people, including Andrew Haley, Marcel
Hendrix, Bernd Paysan, and Elizabeth Rather. If you have been left
out and want acknowledgement, please let me know.

Quotations
==========

Discussion
----------
The essence of quotations is to provide nested colon definitions,
in which the inside definition(s) are namess. The expression

: foo ... [: some words ;] ... ;

is equivalent to

:noname some words ; Constant #temp#
: foo ... #temp# ... ;

If quotations are to have the same privileges as words defined
with : and :NONAME they should be able to use local variables and
use RECURSE. Quotations should not be able to access the locals of
the outer word because we have no knowledge of when the quotation
is executed and hence whether outer locals are still alive.

One example use of quotations is to provide a solution to the use
of CATCH in a form close to other languages' TRY ... EXCEPT
blocks.

: foo
  ...
  [: fee fi fo fum ;] catch if ... then
  ...
;


Specification
-------------

[: ( -- nested-sys )
Compilation: suspends compiling to the current definition, starts a
new
nested definition, and compilation continues with this nested
definition. Outer locals are not visible in the nested definition.
RECURSE applies to the nested definition.

;] ( nested-sys -- )
Compilation: Ends the current nested definition, and resumes
compilation
to the previous current definition. It appends the following run-time
to
the current definition:

run-time: ( -- xt )
xt is the execution token to execute the nested definition.


Closures
========

Discussion
----------
I have chosen to distinguish nameless words intended as closures
by using [[: ... ;]] to define them. I have also chosen to
distinguish the required persistence of data by declaring it using
{{ ... }} which is syntactically like { ... } locals but has very
different persistence requirements.

A quotation can have its own locals, but it can't access the
locals of the outer word. We have Forth compilers which could
access locals from the outer scope, but not as a real closure or
correctly nested frame.

Closures have different requirements for scope (visibility) and for
data persistence.

: foo { a b -- } ... [: ... a b ... ;] execute ;

Here, a and b referenced in the boy-closure are offsets into the
locals
stack which are identical to code generated within foo, and when
executed from within foo directly, they access the same locals.  These
are not real closures, not even correctly nested frames.

Algol 60 (with its famous man-or-boy-test) has nested frames, which
requires that the xt carries a reference to the scope it was created
in,
i.e. [: would produce an xt at run-time, which sets the frame for
access
to outer locals, and then runs the code defined within the [: ;]
boundaries.  Algol-like compilers usually solve that by adding an
implicit paramenter to the nested function, which points to the
environment, and the compiler knows to insert the proper parameter,
but
in Forth, we can't do this.

Full closures go even further, they make sure that the environment is
active as long as the closure (the xt returned after ;]) is alive.
This
means that the locals would be allocated on the heap, an some sort of
garbage collection is necessary to free unused memory.

: foo {{ a b -- }} ... [[: ... a b ... ;]] execute ;

Knuth's Man-Or-Boy test creates a quotation that *modifies* the
outer locals and then recursively calls its host, accessing outer
locals that one might have expected to long gone out of
scope. It forces the quotation implementation to store copies of
*all imaginable* outer locals and make them permanently available.

This can get even more interesting when a closure is required to
remember not only locals, but things like BASE, >IN, arbitrary
variables, file handles, buffer addresses, etc..(*)

Maybe we first need a convincing example of the usefulness of
quotations and closures -- (*) would certainly be useful, but
the cost seems to be a little excessive?

Aside from looking obscure and clever and satisfying the "[x]
can do it, why not Forth?" test, what on earth does this buy you?

What does a closure achieve that cannot be achieved by other
scoping and persistence mechanisms such as a class and an object
with heap allocation?

Specification
-------------

TBD


-- 
Stephen Pelc, stephenXXX@mpeforth.com
MicroProcessor Engineering Ltd - More Real, Less Time
133 Hill Lane, Southampton SO15 5AF, England
tel: +44 (0)23 8063 1441, fax: +44 (0)23 8033 9691
web: http://www.mpeforth.com - free VFX Forth downloads

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Thread

Quotations revisited mhx@iae.nl (Marcel Hendrix) - 2012-07-14 15:55 +0200
  Re: Quotations revisited stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-15 19:26 +0000
    Re: Quotations revisited Bernd Paysan <bernd.paysan@gmx.de> - 2012-07-15 23:53 +0200
    Re: Quotations revisited mhx@iae.nl (Marcel Hendrix) - 2012-07-15 23:54 +0200
      Re: Quotations revisited Bernd Paysan <bernd.paysan@gmx.de> - 2012-07-16 00:48 +0200
        Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-22 15:01 +0000
          Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-23 16:49 +0000
            Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-23 21:39 +0000
              Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-25 13:13 +0000
        Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-22 11:07 -0500
          Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-22 10:21 -0700
            Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-22 12:35 -0500
              Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-22 11:39 -0700
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-22 15:16 -0500
                Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-22 14:35 -0700
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-23 04:18 -0500
                Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-23 12:58 +0000
                Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-23 11:55 -0700
                Re: Quotations revisited BruceMcF <agila61@netscape.net> - 2012-07-23 05:45 -0700
            Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-27 12:41 +0000
      Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-15 14:11 -1000
        Re: Quotations revisited "A. K." <akk@nospam.org> - 2012-07-16 07:47 +0200
          Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-16 13:56 +0000
            Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-16 07:20 -1000
              Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-17 13:49 +0000
        Re: Quotations revisited Mark Wills <markrobertwills@yahoo.co.uk> - 2012-07-16 02:32 -0700
          Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-27 12:58 +0000
        Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-16 04:32 -0500
          Re: Quotations revisited stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-16 11:41 +0000
            Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-16 07:40 -0500
              Re: Quotations revisited stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-16 14:05 +0000
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-16 09:20 -0500
                Re: Quotations revisited stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-16 15:46 +0000
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-16 11:33 -0500
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-16 15:32 +0000
                Re: Quotations revisited stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-16 17:56 +0000
                Re: Quotations revisited Bernd Paysan <bernd.paysan@gmx.de> - 2012-07-16 23:37 +0200
          Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-27 13:05 +0000
            Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-27 08:21 -0500
      Re: Quotations revisited Roelf Toxopeus <rt4all@notthis.hetnet.nl> - 2012-07-16 10:14 +0200
      Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-16 04:23 -0500
        Re: Quotations revisited m.a.m.hendrix@tue.nl - 2012-07-16 03:39 -0700
          Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-16 07:09 -0500
            Re: Quotations revisited mhx@iae.nl (Marcel Hendrix) - 2012-07-16 23:47 +0200
              Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-17 04:14 -0500
                Re: Quotations revisited Coos Haak <chforth@hccnet.nl> - 2012-07-17 17:39 +0200
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-17 12:18 -0500
                Re: Quotations revisited mhx@iae.nl (Marcel Hendrix) - 2012-07-17 20:26 +0200
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-19 16:21 +0000
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-19 15:58 -0700
      Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-16 14:05 +0000
    Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-16 12:47 +0000
      Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-16 08:56 -0500
      Re: Quotations revisited Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2012-07-16 15:04 +0100
        Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-16 09:23 -0500
          Re: Quotations revisited Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2012-07-16 17:38 +0100
            Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-16 12:58 -0500
        Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-16 14:56 +0000
      Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-16 22:53 +0000
        Re: Quotations revisited BruceMcF <agila61@netscape.net> - 2012-07-16 19:59 -0700
          Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-16 17:04 -1000
            Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-17 06:51 +0000
              Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-16 21:39 -1000
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-17 07:48 +0000
                Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-16 22:24 -1000
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-17 10:48 +0000
                Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-17 08:19 -1000
                Re: Quotations revisited Aleksej Saushev <asau@inbox.ru> - 2012-07-18 01:31 +0400
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-19 16:11 +0000
                Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-19 12:41 -1000
                Re: Quotations revisited Aleksej Saushev <asau@inbox.ru> - 2012-07-21 01:24 +0400
                Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-20 16:20 -1000
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-21 03:59 -0700
                Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-21 21:33 -1000
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-22 01:35 -0700
                Re: Quotations revisited Aleksej Saushev <asau@inbox.ru> - 2012-07-22 21:19 +0400
                Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-22 08:15 -1000
                Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-22 11:48 -0700
                Re: Quotations revisited Coos Haak <chforth@hccnet.nl> - 2012-07-22 21:48 +0200
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-22 15:22 -0500
                Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-22 14:50 -0700
                Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-22 15:08 -0700
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-22 15:20 -0700
                Re: Quotations revisited Aleksej Saushev <asau@inbox.ru> - 2012-07-23 03:29 +0400
                Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-22 14:22 -1000
                Re: Quotations revisited Aleksej Saushev <asau@inbox.ru> - 2012-07-23 05:46 +0400
                Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-22 21:46 -1000
                Re: Quotations revisited Aleksej Saushev <asau@inbox.ru> - 2012-07-25 03:31 +0400
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-23 16:50 +0000
                Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-23 07:57 -1000
                Re: Quotations revisited Aleksej Saushev <asau@inbox.ru> - 2012-07-25 03:38 +0400
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-26 13:01 +0000
                Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-21 12:10 +0000
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-21 09:19 -0500
                Re: Quotations revisited Bernd Paysan <bernd.paysan@gmx.de> - 2012-07-21 18:58 +0200
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-22 04:24 -0500
                Re: Quotations revisited Bernd Paysan <bernd.paysan@gmx.de> - 2012-07-22 14:25 +0200
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-22 11:11 -0500
                Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-21 19:29 +0000
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-23 16:31 +0000
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-23 12:21 -0500
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-23 17:32 +0000
                Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-23 11:23 -0700
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-24 03:28 -0500
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-25 13:15 +0000
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-25 11:47 -0500
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-26 13:06 +0000
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-26 09:50 -0500
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-26 15:11 +0000
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-26 11:06 -0500
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-26 16:46 +0000
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-27 04:52 -0500
                Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-26 09:48 -0700
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-27 14:51 +0000
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-28 08:29 -0500
                Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-29 20:55 -0700
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-23 16:17 +0000
                Re: Quotations revisited "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-07-22 18:41 -0400
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-23 16:53 +0000
            Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-17 12:22 +0000
              Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-17 07:30 -0500
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-17 06:34 -0700
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-17 09:04 -0500
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-18 07:07 -0700
                Re: Quotations revisited Coos Haak <chforth@hccnet.nl> - 2012-07-18 17:43 +0200
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-18 09:29 -0700
                Re: Quotations revisited Coos Haak <chforth@hccnet.nl> - 2012-07-18 20:59 +0200
                Re: Quotations revisited Coos Haak <chforth@hccnet.nl> - 2012-07-18 21:14 +0200
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-19 16:05 +0000
                Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-20 14:50 +0000
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-20 15:08 +0000
                Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-21 11:27 +0000
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-23 16:28 +0000
                Re: Quotations revisited Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-23 19:41 +0000
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-18 10:18 -0700
                Re: Quotations revisited anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-19 17:00 +0000
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-19 15:34 -0700
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-19 16:08 -0700
                Re: Quotations revisited Bernd Paysan <bernd.paysan@gmx.de> - 2012-07-17 20:09 +0200
  Re: Quotations revisited stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-16 12:01 +0000
    Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-16 10:42 -0700
      Re: Quotations revisited stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-16 18:06 +0000
        Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-16 11:08 -1000
          Re: Quotations revisited stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-16 21:38 +0000
            Re: Quotations revisited Bernd Paysan <bernd.paysan@gmx.de> - 2012-07-17 00:29 +0200
              Re: Quotations revisited "Elizabeth D. Rather" <erather@forth.com> - 2012-07-16 12:38 -1000
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-17 04:20 -0500
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-17 03:21 -0700
                Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-17 03:14 -0700
                Re: Quotations revisited Bernd Paysan <bernd.paysan@gmx.de> - 2012-07-17 19:58 +0200
                Re: Quotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-17 13:05 -0500
  Re: Quotations revisited stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-20 11:12 +0000
    Re: Quotations revisited Alex McDonald <blog@rivadpm.com> - 2012-07-20 05:40 -0700
      Re: Quotations revisited stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-20 15:55 +0000
    Re: Quotations revisited Paul Rubin <no.email@nospam.invalid> - 2012-07-22 20:54 -0700
      Re: Quotations revisited Aleksej Saushev <asau@inbox.ru> - 2012-07-25 03:55 +0400

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