Groups > comp.lang.forth > #20831

Re: Difficulty with Brad Rodriguez' screenful

From	Andrew Haley <andrew29@littlepinkcloud.invalid>
Subject	Re: Difficulty with Brad Rodriguez' screenful
Newsgroups	comp.lang.forth
References	(2 earlier) <ki35b7$jnn$1@online.de> <hdKdnRluwIcFgdjMnZ2dnUVZ_sadnZ2d@supernews.com> <ki5p5f$ocf$1@online.de> <lIednR2qYrkK3drMnZ2dnUVZ_oydnZ2d@supernews.com> <ki8h50$7qc$1@online.de>
Message-ID	<7_KdnbqH7LjkoNXMnZ2dnUVZ_sWdnZ2d@supernews.com> (permalink)
Date	2013-03-19 05:27 -0500

Show all headers | View raw

Bernd Paysan <bernd.paysan@gmx.de> wrote:
> Andrew Haley wrote:
> 
>> Bernd Paysan <bernd.paysan@gmx.de> wrote:
>>> Manipulating the return stack is a frequently used way to write
>>> backtracking in Forth.  My regexp parser uses the return stack,
>>> Brad's BNF parser uses it somewhat differently.  There is no
>>> "native" control structure in Forth for that purpose.
>> 
>> There's no need to mess about with the return stack just to do
>> backtracking.  THROW does the job adequately.
> 
> But an awful lot slower. 

It probably is in some implementations.  It needn't be.

This is something of a chicken and egg situation: people don't much
use THROW because "it's expensive" and implementers don't bother
optimizing it because it isn't much used.

> So you recommend to keep optimizations which make my code maybe 10%
> faster, and the force me to use something which makes my code 10
> times slower?

I doubt very much that backtracking is a critical speed bottleneck in
your parser, unless your implementation of THROW is catastrophically
bad.  There's nothing intrinsically expensive about THROW , and it has
the virtue of confining its effects to the place where it's needed.
Full optimization can be used everywhere else.

The work that CATCH has to do is pretty small: save a couple of
pointers and a link on the return stack and update a register to point
to that frame.  THROW fetches those pointers from that register and
returns to that point, which removes the link.

I will grant you that the register cache has to be flushed, which is
expensive, but that's also true if you permit arbitrary return stack
manipulation.

Is THROW necessarily much more expensive than

if  <some DROPs> r> r> drop fred @ >r >r else ...

?  

> In any case, THROW does its work by messing around with the return
> stack.

Perhaps, but it is not arbitrary messing around it is much controlled
than that would imply.  The advantage of THROW as a structuring device
is that the place it returns to is marked by the caller.  This avoids
the inversion of control that is caused by messing with the return
stack, in which the caller cannot determine where the code it just
called will return to.  It also permits the calling code to be
refactored.

THROW is just better: it allows more implementation choices and gives
the compiler more opportunities for optimization.  It's a matter for
the implementers to do a good job of optimizing it.

Andrew.

Back to comp.lang.forth | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

Difficulty with Brad Rodriguez' screenful Eduardo Costa <edu500ac@gmail.com> - 2013-03-15 07:10 -0700
  Re: Difficulty with Brad Rodriguez' screenful stephenXXX@mpeforth.com (Stephen Pelc) - 2013-03-15 17:06 +0000
    Re: Difficulty with Brad Rodriguez' screenful Eduardo Costa <edu500ac@gmail.com> - 2013-03-15 11:27 -0700
    Re: Difficulty with Brad Rodriguez' screenful Eduardo Costa <edu500ac@gmail.com> - 2013-03-15 13:06 -0700
    Re: Difficulty with Brad Rodriguez' screenful Eduardo Costa <edu500ac@gmail.com> - 2013-03-15 13:43 -0700
      Re: Difficulty with Brad Rodriguez' screenful "Elizabeth D. Rather" <erather@forth.com> - 2013-03-15 12:17 -1000
        Re: Difficulty with Brad Rodriguez' screenful Eduardo Costa <edu500ac@gmail.com> - 2013-03-16 13:25 -0700
          Re: Difficulty with Brad Rodriguez' screenful mhx@iae.nl (Marcel Hendrix) - 2013-03-17 00:18 +0200
            Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-17 02:13 +0100
              Re: Difficulty with Brad Rodriguez' screenful "Elizabeth D. Rather" <erather@forth.com> - 2013-03-16 15:29 -1000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-18 02:03 +0100
                Re: Difficulty with Brad Rodriguez' screenful "Elizabeth D. Rather" <erather@forth.com> - 2013-03-17 15:23 -1000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-18 04:16 +0100
                Re: Difficulty with Brad Rodriguez' screenful "Elizabeth D. Rather" <erather@forth.com> - 2013-03-17 18:20 -1000
                Re: Difficulty with Brad Rodriguez' screenful stephenXXX@mpeforth.com (Stephen Pelc) - 2013-03-18 13:07 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-18 21:45 +0100
                Re: Difficulty with Brad Rodriguez' screenful Elizabeth D Rather <erather@forth.com> - 2013-03-18 12:13 -1000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 03:46 +0100
                Re: Difficulty with Brad Rodriguez' screenful stephenXXX@mpeforth.com (Stephen Pelc) - 2013-03-19 09:42 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 17:04 +0100
                Re: Difficulty with Brad Rodriguez' screenful stephenXXX@mpeforth.com (Stephen Pelc) - 2013-03-19 17:54 +0000
                Re: Difficulty with Brad Rodriguez' screenful Brad Eckert <hwfwguy@gmail.com> - 2013-03-19 13:30 -0700
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 22:33 +0100
                Re: Difficulty with Brad Rodriguez' screenful albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-03-19 13:03 +0000
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-19 14:56 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 21:55 +0100
                Re: Difficulty with Brad Rodriguez' screenful Alex McDonald <blog@rivadpm.com> - 2013-03-19 14:16 -0700
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-20 02:09 +0100
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-02 16:44 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-02 22:07 +0200
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 20:35 +0100
                Re: Difficulty with Brad Rodriguez' screenful stephenXXX@mpeforth.com (Stephen Pelc) - 2013-03-19 09:52 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 18:56 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-19 13:18 -0500
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 22:37 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-20 03:33 -0500
                Re: Difficulty with Brad Rodriguez' screenful "Rod Pemberton" <do_not_have@notemailnotq.cpm> - 2013-03-20 05:30 -0400
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-18 11:28 -0500
                Re: Difficulty with Brad Rodriguez' screenful Alex McDonald <blog@rivadpm.com> - 2013-03-18 15:39 -0700
                Re: Difficulty with Brad Rodriguez' screenful albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-03-19 13:07 +0000
                Re: Difficulty with Brad Rodriguez' screenful m.a.m.hendrix@tue.nl - 2013-03-19 06:58 -0700
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 03:05 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-19 05:27 -0500
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 19:24 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-20 03:42 -0500
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-20 03:54 -0500
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-20 17:49 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-20 12:51 -0500
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-20 20:25 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-21 04:31 -0500
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-21 16:31 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-21 14:48 -0500
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-21 18:07 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-21 14:49 -0500
                Re: Difficulty with Brad Rodriguez' screenful Coos Haak <chforth@hccnet.nl> - 2013-03-22 00:07 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-21 18:31 -0500
                Re: Difficulty with Brad Rodriguez' screenful Coos Haak <chforth@hccnet.nl> - 2013-03-22 00:48 +0100
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-22 01:49 +0100
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-27 17:30 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-22 03:57 -0500
                Re: Difficulty with Brad Rodriguez' screenful Alex McDonald <blog@rivadpm.com> - 2013-03-22 03:39 -0700
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-22 09:03 -0500
                Re: Difficulty with Brad Rodriguez' screenful Alex McDonald <blog@rivadpm.com> - 2013-03-23 08:13 -0700
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-23 12:39 -0500
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-23 14:19 -0500
                Re: Difficulty with Brad Rodriguez' screenful Alex McDonald <blog@rivadpm.com> - 2013-03-23 13:01 -0700
                Re: Difficulty with Brad Rodriguez' screenful Brad Eckert <hwfwguy@gmail.com> - 2013-03-22 08:13 -0700
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-22 14:44 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-22 10:34 -0500
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-22 15:39 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-22 20:38 +0100
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-22 20:54 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-22 12:27 -0500
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-22 17:38 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-22 13:48 -0500
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-23 11:53 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-24 01:46 +0100
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-27 17:04 +0000
                Re: Difficulty with Brad Rodriguez' screenful Brad Eckert <hwfwguy@gmail.com> - 2013-03-25 10:06 -0700
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-19 16:05 +0000
                Re: Difficulty with Brad Rodriguez' screenful Alex McDonald <blog@rivadpm.com> - 2013-03-19 12:32 -0700
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-18 18:28 +0000
              Re: Difficulty with Brad Rodriguez' screenful stephenXXX@mpeforth.com (Stephen Pelc) - 2013-03-18 12:40 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-18 17:23 +0100
                Re: Difficulty with Brad Rodriguez' screenful stephenXXX@mpeforth.com (Stephen Pelc) - 2013-03-18 17:35 +0000
                Re: Difficulty with Brad Rodriguez' screenful Brad Eckert <hwfwguy@gmail.com> - 2013-03-18 11:02 -0700
                Re: Difficulty with Brad Rodriguez' screenful "WJ" <w_a_x_man@yahoo.com> - 2013-03-19 03:25 +0000
                Re: Difficulty with Brad Rodriguez' screenful albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-03-18 19:35 +0000
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-18 18:17 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 03:29 +0100
                Re: Difficulty with Brad Rodriguez' screenful Paul Rubin <no.email@nospam.invalid> - 2013-03-19 00:06 -0700
                Re: Difficulty with Brad Rodriguez' screenful Paul Rubin <no.email@nospam.invalid> - 2013-03-19 00:11 -0700
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 16:16 +0100
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-19 15:06 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-19 22:27 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-20 03:49 -0500
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-20 11:09 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-20 10:25 -0500
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-20 18:08 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-20 13:04 -0500
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-20 20:12 +0100
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-21 04:39 -0500
                Re: Difficulty with Brad Rodriguez' screenful albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-03-20 19:22 +0000
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-30 17:35 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-03-31 08:51 -0500
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-02 15:50 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-02 16:16 -0500
                Re: Difficulty with Brad Rodriguez' screenful Alex McDonald <blog@rivadpm.com> - 2013-03-20 10:27 -0700
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-20 12:03 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-20 18:47 +0100
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-03-30 16:40 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-01 02:12 +0200
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-01 16:58 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-02 04:20 +0200
                Re: Difficulty with Brad Rodriguez' screenful "Elizabeth D. Rather" <erather@forth.com> - 2013-04-01 16:39 -1000
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-02 14:15 +0000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-02 21:12 +0200
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-02 04:17 -0500
                Re: Difficulty with Brad Rodriguez' screenful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-02 15:35 +0000
                Re: Difficulty with Brad Rodriguez' screenful Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-02 16:36 -0500
            Re: Difficulty with Brad Rodriguez' screenful Eduardo Costa <edu500ac@gmail.com> - 2013-03-16 22:27 -0700
              Re: Difficulty with Brad Rodriguez' screenful mhx@iae.nl (Marcel Hendrix) - 2013-03-17 10:10 +0200
                Re: Difficulty with Brad Rodriguez' screenful mhx@iae.nl (Marcel Hendrix) - 2013-03-17 18:15 +0200
                Re: Difficulty with Brad Rodriguez' screenful Eduardo Costa <edu500ac@gmail.com> - 2013-03-17 13:00 -0700
                Re: Difficulty with Brad Rodriguez' screenful mhx@iae.nl (Marcel Hendrix) - 2013-03-17 23:34 +0200
                Re: Difficulty with Brad Rodriguez' screenful Eduardo Costa <edu500ac@gmail.com> - 2013-03-17 16:44 -0700
                Re: Difficulty with Brad Rodriguez' screenful "WJ" <w_a_x_man@yahoo.com> - 2013-03-17 23:53 +0000
                Re: Difficulty with Brad Rodriguez' screenful mhx@iae.nl (Marcel Hendrix) - 2013-03-18 23:32 +0200
                Re: Difficulty with Brad Rodriguez' screenful Lars Brinkhoff <lars.spam@nocrew.org> - 2013-03-19 08:12 +0100
                Re: Difficulty with Brad Rodriguez' screenful m.a.m.hendrix@tue.nl - 2013-03-19 00:33 -0700
                Re: Difficulty with Brad Rodriguez' screenful Lars Brinkhoff <lars.spam@nocrew.org> - 2013-03-19 09:39 +0100
                Re: Difficulty with Brad Rodriguez' screenful mhx@iae.nl (Marcel Hendrix) - 2013-03-19 21:11 +0200
                Re: Difficulty with Brad Rodriguez' screenful Elizabeth D Rather <erather@forth.com> - 2013-03-19 10:30 -1000
                Re: Difficulty with Brad Rodriguez' screenful Roelf Toxopeus <rt4all@notthis.hetnet.nl> - 2013-03-19 22:31 +0100
                Re: Difficulty with Brad Rodriguez' screenful Elizabeth D Rather <erather@forth.com> - 2013-03-19 12:09 -1000
                Re: Difficulty with Brad Rodriguez' screenful Bernd Paysan <bernd.paysan@gmx.de> - 2013-03-18 19:23 +0100
      Re: Difficulty with Brad Rodriguez' screenful stephenXXX@mpeforth.com (Stephen Pelc) - 2013-03-16 06:34 +0000
  Re: Difficulty with Brad Rodriguez' screenful junnia@gmail.com - 2013-03-19 07:45 -0700
    Re: Difficulty with Brad Rodriguez' screenful mhx@iae.nl (Marcel Hendrix) - 2013-03-19 21:38 +0200
      Re: Difficulty with Brad Rodriguez' screenful mhx@iae.nl (Marcel Hendrix) - 2013-03-23 01:31 +0200

csiph-web