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Groups > comp.lang.forth > #40962
| From | Bernd Linsel <bl1@gmx.com> |
|---|---|
| Newsgroups | comp.lang.forth |
| Subject | Re: RfD: Quotations |
| Date | 2015-07-30 14:00 +0200 |
| Organization | news.netcologne.de |
| Message-ID | <mpd3la$6fk$1@newsreader4.netcologne.de> (permalink) |
| References | (6 earlier) <mpb25r$fg4$1@dont-email.me> <mpbo6b$bkf$1@newsreader4.netcologne.de> <mpcm2n$gnf$1@dont-email.me> <mpcsv0$1hu$1@newsreader4.netcologne.de> <mpcto9$bkg$1@dont-email.me> |
Am 30.07.2015 um 12:21 schrieb Alex McDonald:> on 30/07/2015 11:06:25,
Bernd Linsel wrote:
>> For every child in the call chain of a function, the local variables
>> of the functions above (invoked before) seem to be global, as all
>> children are accessing the same instance of that
>> parent's/grandparent's/grand-... local variable.
>> (Presuming dynamic scoping or nested definitions, like quotations)
>
> Dynamic scoping? That's not what you said.
Normally, scope (symbol visibilty) and extent (variable lifetime) in
Forth don't impose great problems, because nested definitions are not
allowed. However, when quotations that can be invoked outside the
creating word's runtime, it must be considered.
Shortly outlined and drastically reduced:
- Static scope: Nested definitions have access to outer definitions' locals.
- Dynamic scope: Nested *invocations* have access to earlier invoked
functions' locals.
- Global Forth variables have infinite extent (their value stays valid
as long as the dictionary is not cleared).
- Local Forth variables have static extent (their value is valid from
their definition/initialization until the containing word returns).
Quotations in Forth suddenly introduce nested definitions.
And if a quotation (q) has somehow access to the locals of the word it
was defined in (p, for parent), you have a mix of static and dynamic
scoping:
Static, because q's definition is nested in p's definition. As long as
you call q from within p, q can just access p's locals stack frame.
But if p returns q (respectively an xt for q) and exits, then q is
invoked later, p's locals stack frame ceased to exist. Any reference to
p's locals is invalid. But in q's "history" there has been the
invocation of p that created q. So now you have a kind of dynamic
scoping -- iff there is a mechanism that keeps the locals of p alive in
order to let q access them even after p returned.
This is not straightforward dynamic scoping after the schoolbook, but in
the same category.
> <quote>
> To approximate this behaviour, I suggest making accessed parent's locals
> static copies, or if you prefer, globals with special scope, just
> visible withing the quotation.
> </quote>
>
> and
>
> <quote>
> - parent's locals become 'static locals' when accessed within the
> quotation, mainly because of the effect of being able to store state
> (what admittedly may equally be achieved by using globals).
> </quote>
>
> Can you provide an example or two?
>
> On reading agan the post that these come from, I would also like an
> example of the issues you raise there, since I don't understand it
> either.
>
> <quote>
> The suggested RfD lacks the possibility for a simple way to pass values
> into the quotation at creation time (if the parameter stack is used as
> compilation stack, as ISO 94 and 200x suggest / allow), and the
> possibility to create aggregating quotations without a global variable
> accessible and visible to the "outer world".
> </quote>
>
> Thanks.
>
#1 passing values into a quotation
The best example is currying, e.g. reducing the arity of a function by
providing some (but not all) arguments to it, creating another
"specialized" function:
: f ( x y -- z )
dup * \ x y²
swap * \ y² x²
+
;
: curry { xt1 x -- xt2 }
[: x swap xt1 execute :] ( y -- z )
;
# 3 4 f . \ => 25 ok
# defer f3 \ => ok
# ' f 3 curry is f3 \ => ok ( f3 is the same as 3 ? f )
4 f3 . \ => 25 ok ( 4 f3 is the same as 3 4 f )
#2 storing state within a quotation
: begin-sum ( -- xt )
0 { sum } \ create local state variable for the sum
[: sum + dup to sum :] ( n -- sum )
;
# defer sum-add \ => ok
# begin-sum is sum-add \ => ok
# 3 sum-add . \ => 3 ok
# 2 sum-add . \ => 5 ok
# 1 sum-add drop \ => ok ( sum=6 )
# 4 sum-add drop \ => ok ( sum=10 )
# 3 sum-add . \ => 13 ok
and...
# begin-sum is sum-add \ => ok ( new instance, sum=0 )
# : test
# 10 0 do
# i sum-add drop
# loop
# 0 sum-add ; \ => ok
# test . \ => 45 ok
#3 passing value into the quotation's definition
: begin-sum-with-start { sum -- xt } \ initial value not null but
provided by caller
[: sum + dup to sum :] ( n -- sum )
;
# 8 begin-sum-with-start is sum-add
# 1 sum-add drop
# 2 sum-add drop
# 3 sum-add . \ => 14 ok
Got the point?
--
Best regards,
Bernd
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RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-28 21:22 +0100
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-29 07:35 +0000
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-29 14:20 +0100
Re: RfD: Quotations Ron Aaron <rambamist@gmail.com> - 2015-07-29 13:44 +0300
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-29 13:42 +0100
Re: RfD: Quotations Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-29 05:35 -0700
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-29 13:34 +0000
Re: RfD: Quotations Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-29 07:35 -0700
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-29 15:05 +0000
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-29 16:19 +0100
Re: RfD: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2015-07-29 21:48 +0100
Re: RfD: Quotations mhx@iae.nl - 2015-07-29 11:13 -0700
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-30 13:04 +0000
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-29 15:07 +0100
Re: RfD: Quotations Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-29 07:44 -0700
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-29 15:12 +0000
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-29 16:18 +0100
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-29 18:37 +0200
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-29 17:55 +0100
Re: RfD: Quotations "Elizabeth D. Rather" <erather@forth.com> - 2015-07-29 19:51 -0500
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-30 03:31 +0200
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-07-29 19:30 -0700
Re: RfD: Quotations Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-29 21:19 -0700
Re: RfD: Quotations Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-29 21:37 -0700
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-30 11:45 +0000
Re: RfD: Quotations Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-30 08:07 -0700
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-31 10:54 +0000
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 12:48 +0100
Re: RfD: Quotations Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-31 05:40 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 14:46 +0100
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 14:50 +0100
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-31 14:46 +0000
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-07-31 13:16 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 21:49 +0100
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-07-29 22:42 -0700
Re: RfD: Quotations "Elizabeth D. Rather" <erather@forth.com> - 2015-07-30 08:46 -0500
Re: RfD: Quotations Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-29 21:40 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-30 10:01 +0100
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-30 12:00 +0200
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-30 11:10 +0100
Re: RfD: Quotations Coos Haak <chforth@hccnet.nl> - 2015-07-30 16:35 +0200
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-29 16:53 +0000
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-29 19:03 +0200
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-29 18:24 +0100
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-30 01:38 +0200
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-30 09:10 +0100
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-30 12:06 +0200
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-30 11:21 +0100
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-30 14:00 +0200
Re: RfD: Quotations franck.bensusan@gmail.com - 2015-07-30 06:59 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 10:53 +0100
Re: RfD: Quotations Paul Rubin <no.email@nospam.invalid> - 2015-07-29 10:35 -0700
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-30 01:45 +0200
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-30 03:17 +0200
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-07-29 19:21 -0700
Re: RfD: Quotations Paul Rubin <no.email@nospam.invalid> - 2015-07-29 23:04 -0700
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-30 12:38 +0200
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-30 12:09 +0100
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-30 13:26 +0200
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 09:47 +0100
Re: RfD: Quotations Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-31 02:51 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 11:21 +0100
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-30 09:11 +0100
Re: RfD: Quotations Paul Rubin <no.email@nospam.invalid> - 2015-07-29 11:36 -0700
Re: RfD: Quotations Paul Rubin <no.email@nospam.invalid> - 2015-07-29 11:37 -0700
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-30 13:07 +0000
Re: RfD: Quotations Bernd Linsel <bl1@gmx.com> - 2015-07-30 16:25 +0200
Re: RfD: Quotations mhx@iae.nl - 2015-07-29 11:16 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-29 20:27 +0100
Re: RfD: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2015-07-29 21:57 +0100
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-29 22:48 +0100
Re: RfD: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2015-07-31 12:34 +0100
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 13:00 +0100
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-31 14:31 +0000
Re: RfD: Quotations mhx@iae.nl - 2015-07-31 11:32 -0700
Re: RfD: Quotations mhx@iae.nl - 2015-07-29 21:42 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-30 09:57 +0100
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-07-29 17:21 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-30 09:56 +0100
Re: RfD: Quotations franck.bensusan@gmail.com - 2015-07-30 04:15 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-30 12:30 +0100
Re: RfD: Quotations franck.bensusan@gmail.com - 2015-07-30 05:04 -0700
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-07-30 13:07 -0700
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-07-29 16:52 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-30 09:53 +0100
Re: RfD: Quotations Bernd Paysan <bernd.paysan@gmx.de> - 2015-07-30 21:45 +0200
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-07-30 13:25 -0700
Re: RfD: Quotations Julian Fondren <ayrnieu@gmail.com> - 2015-07-30 15:11 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 09:11 +0100
Re: RfD: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2015-07-31 12:04 +0100
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-30 22:51 +0100
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-07-30 22:38 -0700
Re: RfD: Quotations "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-07-31 02:10 -0400
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 09:01 +0100
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-08-01 14:59 -0700
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-08-01 23:36 +0100
Re: RfD: Quotations Bernd Paysan <bernd.paysan@gmx.de> - 2015-08-02 01:19 +0200
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-08-01 18:27 -0700
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-08-09 14:34 -0700
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-31 08:52 +0000
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 11:57 +0100
Re: RfD: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2015-07-31 21:42 +0100
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-07-31 22:25 +0100
Re: RfD: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2015-07-31 23:39 +0100
Re: RfD: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2015-08-01 10:59 +0100
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-08-01 14:18 +0000
Re: RfD: Quotations Bernd Paysan <bernd.paysan@gmx.de> - 2015-08-01 22:10 +0200
Re: RfD: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-08-02 05:36 +0000
Re: RfD: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2015-08-03 16:40 +0100
Re: RfD: Quotations "Alex McDonald" <blog@rivadpm.com> - 2015-08-03 18:02 +0100
Re: RfD: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2015-08-03 20:22 +0100
Re: RfD: Quotations Coos Haak <chforth@hccnet.nl> - 2015-08-04 02:10 +0200
Re: RfD: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2015-08-04 08:49 +0100
Re: RfD: Quotations hughaguilar96@gmail.com - 2015-08-01 15:15 -0700
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