Re: local variable

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: local variable
Date	2015-07-11 13:42 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2015Jul11.154246@mips.complang.tuwien.ac.at> (permalink)
References	(6 earlier) <mnof8f$tst$1@dont-email.me> <ebe5f448-5311-4949-83c8-e420c71e7080@googlegroups.com> <mnoo9j$1ck$1@dont-email.me> <40c66af5-0dab-46b6-aafe-60aad5b38337@googlegroups.com> <mnosts$jps$1@dont-email.me>

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"Alex McDonald" <blog@rivadpm.com> writes:
>C++ has closures but no GC
>http://www.cprogramming.com/c++11/c++11-lambda-closures.html

They are not fully capable closures, although C++ tries to give you as
much as is possible without requiring GC; the section "How are Lambda
Closures Implemented?" are most enlightening in this respect: So you
can capture referenced variables by-reference (i.e., you access the
original variable through a pointer), but then you must not pass the
lambda outside the scope(s) of the captured variables; or you can
capture the variable by making a copy, then any changes to the
captured variable do not affect the original or any other lamda that
also captures the original variable.

Both options fall short of the power of full-blown closures; e.g., you
cannot implement objects based on C++ lambdas, which you can do with
full-blown closures.

Both options have been proposed as ways to allow outer locals in
Forth.  I think we will have to see whether these options give enough
benefit to justify their implementation cost.

>> It's about high order words (like "map", "filter", "apply", etc. see
>> Oforth, see Factor) in strong relation with data structures.
>
>I get that, but I was wondering what the benefit of using outer locals in
>quotations might be.

If the higher-order word calls a word with the stack effect n1 -- n2,
and you want to pass additional arguments, it would be nice if you
could pass these arguments through a local variable; e.g.

( addr u ) [: n + ;] foreach 

Bernd Paysan thinks we don't need that, and that we can use the stack
for passing additional stuff; so here we would do it as follows:

n ( addr u ) [: over + ;] foreach drop

I am not convinced that this is good enough in every case, but the
question is if the cases where this technique is too cumbersome or
impossible are frequent enough to matter.  I think we should go with
it for a while, until we know where the limits of this technique are.

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2015: http://www.mpeforth.com/euroforth2015/euroforth2015.htm

Thread

Re: local variable hughaguilar96@gmail.com - 2015-07-04 19:52 -0700
  Re: local variable "Alex McDonald" <blog@rivadpm.com> - 2015-07-05 07:24 +0100
    Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-05 02:04 -0700
      Re: local variable "Alex McDonald" <blog@rivadpm.com> - 2015-07-05 10:36 +0100
        Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-05 03:25 -0700
          Re: local variable Bernd Paysan <bernd.paysan@gmx.de> - 2015-07-05 15:28 +0200
            Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-05 08:11 -0700
              Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-05 08:21 -0700
                Re: local variable Bernd Paysan <bernd.paysan@gmx.de> - 2015-07-05 23:53 +0200
                Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-05 20:31 -0700
            Re: local variable hughaguilar96@gmail.com - 2015-07-05 19:56 -0700
        Re: local variable hughaguilar96@gmail.com - 2015-07-05 19:57 -0700
          Re: local variable "Alex McDonald" <blog@rivadpm.com> - 2015-07-06 08:09 +0100
            Re: local variable hughaguilar96@gmail.com - 2015-07-06 19:59 -0700
              Re: local variable "Alex McDonald" <blog@rivadpm.com> - 2015-07-07 08:30 +0100
                Re: local variable Michael Barry <barrym95838@yahoo.com> - 2015-07-10 00:35 -0700
                Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-10 01:41 -0700
                Re: local variable "Alex McDonald" <blog@rivadpm.com> - 2015-07-10 13:55 +0100
                Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-10 07:13 -0700
                Re: local variable "Alex McDonald" <blog@rivadpm.com> - 2015-07-10 16:29 +0100
                Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-10 08:57 -0700
                Re: local variable "Alex McDonald" <blog@rivadpm.com> - 2015-07-10 17:48 +0100
                Re: local variable Paul Rubin <no.email@nospam.invalid> - 2015-07-10 10:02 -0700
                Re: local variable "WJ" <w_a_x_man@yahoo.com> - 2015-09-16 17:30 +0000
                Re: local variable Mark Wills <markwills1970@gmail.com> - 2015-07-10 10:28 -0700
                Re: local variable "Elizabeth D. Rather" <erather@forth.com> - 2015-07-10 08:00 -1000
                Re: local variable hughaguilar96@gmail.com - 2015-07-10 21:31 -0700
                Re: local variable "Alex McDonald" <blog@rivadpm.com> - 2015-07-10 19:13 +0100
                Re: local variable "Elizabeth D. Rather" <erather@forth.com> - 2015-07-10 09:06 -1000
                Re: local variable anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-11 14:10 +0000
                Re: local variable humptydumpty <ouatubi@gmail.com> - 2015-07-11 10:14 -0700
                Re: local variable anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-12 15:56 +0000
                Re: local variable humptydumpty <ouatubi@gmail.com> - 2015-07-12 11:48 -0700
                Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-10 21:21 -0700
                Re: local variable hughaguilar96@gmail.com - 2015-07-10 21:56 -0700
                Re: local variable "Alex McDonald" <blog@rivadpm.com> - 2015-07-11 23:51 +0100
                Re: local variable anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-11 13:42 +0000
                Re: local variable franck.bensusan@gmail.com - 2015-07-12 02:17 -0700
                Re: local variable anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-12 15:12 +0000
                Re: local variable franck.bensusan@gmail.com - 2015-07-13 02:37 -0700
                Re: local variable anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-13 16:13 +0000
                Re: local variable franck.bensusan@gmail.com - 2015-07-13 14:48 -0700
                Re: local variable anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-14 06:41 +0000
                Re: local variable franck.bensusan@gmail.com - 2015-07-14 01:44 -0700
                Re: local variable Bernd Linsel <bl1@gmx.com> - 2015-07-11 11:03 +0200
                Re: local variable Bernd Linsel <bl1@gmx.com> - 2015-07-11 11:11 +0200
                Re: local variable hughaguilar96@gmail.com - 2015-07-12 16:43 -0700
                Re: local variable anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-11 15:14 +0000
                Re: local variable Julian Fondren <julian.fondren@gmail.com> - 2015-07-11 17:57 -0700
                Re: local variable anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-07-12 15:32 +0000
                Re: local variable "Alex McDonald" <blog@rivadpm.com> - 2015-07-10 13:13 +0100
                Re: local variable hughaguilar96@gmail.com - 2015-07-10 21:48 -0700
      Re: local variable franck.bensusan@gmail.com - 2015-07-05 03:47 -0700
        Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-05 04:15 -0700
          Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-05 04:27 -0700
            Re: local variable Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-07-05 04:39 -0700
          Re: local variable franck.bensusan@gmail.com - 2015-07-05 07:08 -0700

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