Re: Implementing lisp in Forth. Chapter 4.

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From	Paul Rubin <no.email@nospam.invalid>
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Subject	Re: Implementing lisp in Forth. Chapter 4.
Date	Fri, 09 Sep 2016 13:06:00 -0700
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albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) writes:
>>2. Add a gc.fs-style conservative gc to ALLOCATE.
> My marking of the pieces in use will be exact, so it is not a
> conservative gc.

That complicates things somewhat but you get the benefit of an exact gc,
so fine.  I think Guile uses conservative gc partly to make writing C
extensions easier: they don't have to think about making sure
intermediate values are marked or how to mark any Lisp pointer that
might appear in a C structure, etc.  But requiring gc-aware extensions
isn't unbearable.

> Then I've not given up on the idea to just free things here and there
> which would work well with my allocator.

Well, it's a cost (complexity) vs benefit (speed-up) trade-off unless
you're worried about the gc missing stuff.

> In particular there will be no fragmentation issues. Why is it that
> I don't here about fragmentation in this context (of lisp)

With a conservative gc you can't prevent fragmentation.  The simplest
and most traditional exact gc (straightforward mark and sweep) doesn't
prevent fragmentation either.  Emacs has used non-compacting (except for
strings) mark/sweep for the past 30 years unless they changed it, and it
hasn't been a significant problem afaik.

If you want to defragment, the basic approaches are mark-and-compact, or
stop-and-copy.  Both of them relocating objects, which means any
pointers to those objects have to be updated.  Within those approaches
there are generational schemes that can improve performance a lot.
Hedgehog Lisp (https://github.com/sbp/hedgehog) has a simple
2-generation copying gc that you might examine.  There are some other
methods like having separate pages for each type of fixed-size object
("BIBOP", BIg Bag Of Pages) that I think have fallen into disuse.

In my experience, if you have a reasonable amount of memory, gc
performance isn't a big issue unless you've got a backend that generates
native machine code.  Otherwise your interpreter will spend most of its
time running user code rather than gc.

Here's a nice page about the Factor gc that I just happened to look at:

http://factor-language.blogspot.com/2009/11/mark-compact-garbage-collection-for.html

Factor uses a mark-compact scheme inspired by Clojure, that's also
described in the 2011 Jones et al book that's been mentioned here a few
times.

> I'm referring to a trivial extension to Forth: if the search fails
> and it is not a number, you've the option to execute some word.

I think you want to be able to call a user word even if the search
doesn't fail, or it's a number.  E.g. you may have to treat Lisp numbers
differently than Forth numbers.

>>Not sure what you mean: an existing Lisp in C?
> Indeed. Also about 1000 lines

Which one is that, if I can ask?  Is it online?

Thread

Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-08-29 18:41 +0200
  Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-08-29 09:39 -0700
    Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-08-30 10:49 +0200
  Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-08-29 09:46 -0700
    Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-08-30 11:07 +0200
      Re: Implementing lisp in Forth. Chapter 4. Rod Pemberton <NoHaveNotOne@zxdehrnyya.cam> - 2016-08-30 08:00 -0400
        Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-02 12:34 +0200
      Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-08-31 14:23 -0700
        Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-01 02:15 +0200
          Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-01 19:49 -0700
            Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-02 11:49 +0200
              Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-04 11:28 -0700
                Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-05 03:31 +0200
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-04 21:03 -0700
                Re: Implementing lisp in Forth. Chapter 4. Spiros Bousbouras <spibou@gmail.com> - 2016-09-05 07:47 +0000
                Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-05 12:05 +0200
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-05 12:04 -0700
                Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-06 11:48 +0200
                Re: Implementing lisp in Forth. Chapter 4. Spiros Bousbouras <spibou@gmail.com> - 2016-09-06 15:32 +0000
                Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-06 21:27 +0200
                Re: Implementing lisp in Forth. Chapter 4. anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-09-06 19:50 +0000
                Re: Implementing lisp in Forth. Chapter 4. Stefan Monnier <monnier@iro.umontreal.ca> - 2016-09-08 12:15 -0400
                Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-08 20:09 +0200
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-08 12:34 -0700
                Re: Implementing lisp in Forth. Chapter 4. anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-09-12 10:17 +0000
                Re: Implementing lisp in Forth. Chapter 4. Stefan Monnier <monnier@iro.umontreal.ca> - 2016-09-12 11:50 -0400
                Re: Implementing lisp in Forth. Chapter 4. anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-09-12 16:48 +0000
                Re: Implementing lisp in Forth. Chapter 4. Stefan Monnier <monnier@iro.umontreal.ca> - 2016-09-12 13:41 -0400
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-06 22:03 -0700
                Re: Implementing lisp in Forth. Chapter 4. George Neuner <gneuner2@comcast.net> - 2016-09-08 16:50 -0400
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-08 16:34 -0700
                Re: Implementing lisp in Forth. Chapter 4. George Neuner <gneuner2@comcast.net> - 2016-09-09 00:12 -0400
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-08 22:22 -0700
                Re: Implementing lisp in Forth. Chapter 4. Lars Brinkhoff <lars.spam@nocrew.org> - 2016-09-27 08:51 +0200
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-27 00:47 -0700
                Re: Implementing lisp in Forth. Chapter 4. Spiros Bousbouras <spibou@gmail.com> - 2016-09-06 13:18 +0000
                Re: Implementing lisp in Forth. Chapter 4. "WJ" <w_a_x_man@yahoo.com> - 2016-09-06 20:52 +0000
                Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-11-02 19:15 +0100
                Re: Implementing lisp in Forth. Chapter 4. Lars Brinkhoff <lars.spam@nocrew.org> - 2016-09-09 10:05 +0200
                Re: Implementing lisp in Forth. Chapter 4. anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-09-12 10:11 +0000
                Re: Implementing lisp in Forth. Chapter 4. Lars Brinkhoff <lars.spam@nocrew.org> - 2016-09-12 13:15 +0200
                Re: Implementing lisp in Forth. Chapter 4. anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-09-12 17:25 +0000
                Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-09 16:19 +0200
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-09 10:55 -0700
                Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-09 21:39 +0200
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-09 13:06 -0700
                Re: Implementing lisp in Forth. Chapter 4. franck.bensusan@gmail.com - 2016-09-10 07:23 -0700
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-11 01:28 -0700
                Re: Implementing lisp in Forth. Chapter 4. Spiros Bousbouras <spibou@gmail.com> - 2016-09-13 21:37 +0000
                Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-14 09:55 +0200
                Re: Implementing lisp in Forth. Chapter 4. franck.bensusan@gmail.com - 2016-09-14 01:04 -0700
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-13 14:40 -0700
                Re: Implementing lisp in Forth. Chapter 4. franck.bensusan@gmail.com - 2016-09-14 03:37 -0700
                Re: Implementing lisp in Forth. Chapter 4. lawrencedo99@gmail.com - 2016-09-10 01:17 -0700
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-10 12:01 -0700
                Re: Implementing lisp in Forth. Chapter 4. lawrencedo99@gmail.com - 2016-09-10 21:57 -0700
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-10 22:12 -0700
                Re: Implementing lisp in Forth. Chapter 4. lawrencedo99@gmail.com - 2016-09-10 23:30 -0700
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-10 23:48 -0700
                Re: Implementing lisp in Forth. Chapter 4. Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-09-11 02:59 -0500
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-11 01:16 -0700
                Re: Implementing lisp in Forth. Chapter 4. lawrencedo99@gmail.com - 2016-09-11 19:02 -0700
                Re: Implementing lisp in Forth. Chapter 4. lawrencedo99@gmail.com - 2016-09-11 19:00 -0700
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-10 12:08 -0700
                Re: Implementing lisp in Forth. Chapter 4. anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-09-12 09:43 +0000
                Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-12 13:42 +0200
                Re: Implementing lisp in Forth. Chapter 4. anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-09-12 17:26 +0000
                Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-12 20:56 +0200
                Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-12 13:08 -0700
                Re: Implementing lisp in Forth. Chapter 4. anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-09-14 07:38 +0000
    Re: Implementing lisp in Forth. Chapter 4. Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2016-09-30 07:48 +0100
      Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-30 11:22 +0200
      Re: Implementing lisp in Forth. Chapter 4. Paul Rubin <no.email@nospam.invalid> - 2016-09-30 18:36 -0700
        Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-10-01 11:19 +0200
          Re: Implementing lisp in Forth. Chapter 4. luser droog <mijoryx@yahoo.com> - 2016-10-01 19:34 -0700
  Implementing lisp in Forth. Garbage collection. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-06 12:30 +0200
    Re: Implementing lisp in Forth. Garbage collection. Spiros Bousbouras <spibou@gmail.com> - 2016-09-06 15:34 +0000
      Re: Implementing lisp in Forth. Garbage collection. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-06 21:12 +0200
    Re: Implementing lisp in Forth. Garbage collection. Paul Rubin <no.email@nospam.invalid> - 2016-09-06 14:52 -0700
      Re: Implementing lisp in Forth. Garbage collection. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-09-07 01:50 +0200
        Re: Implementing lisp in Forth. Garbage collection. Paul Rubin <no.email@nospam.invalid> - 2016-09-06 17:49 -0700
  Re: Implementing lisp in Forth. Chapter 4. luser droog <mijoryx@yahoo.com> - 2016-10-21 17:02 -0700
    Re: Implementing lisp in Forth. Chapter 4. albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-10-22 02:43 +0200

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