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From: Tom Lord <lord@emf.net>
Cc: guile-user@gnu.org, guile-devel@gnu.org
Subject: Re: Worrying development
Date: Fri, 23 Jan 2004 14:18:25 -0800 (PST)	[thread overview]
Message-ID: <200401232218.OAA27477@morrowfield.regexps.com> (raw)
In-Reply-To: <87oesus7kg.fsf@zagadka.ping.de> (message from Marius Vollmer on Fri, 23 Jan 2004 22:01:35 +0100)



    > From: Marius Vollmer <mvo@zagadka.de>
    > Tom Lord <lord@emf.net> writes:
    > > Mutation-sharing shared substrings are an upwards compatible extension
    > > to the Scheme standard.  They break no correct programs.  They enable
    > > new kinds of programs.

    > I'd say that the real 'trouble' is that strings are mutable at
    > all.

Worried mostly about variable-length character encodings in string?
Or you'd just rather be programming in an ML-family language? :-)

If it's variable-length encodings that irk you:  if strings were
read-only you'd want to optimize the heck out of STRING-APPEND and
SUBSTRING and, once you did that, you'd have essentially enough
machinery to do mutations efficiently.


    > Also, I still like the idea of using mutation-sharing substrings as
    > markers that allow O(1) access into variable-width encoded strings.

Interesting.  The interaction with STRING-SET! will be tricky.  I
think you'll either have to "timestamp" strings (one tick per mutation
-- and you'll likely have to use a GC'ed value rather than an inline
integer for timestamps) or wind up with O(K) for mutations where K is
the number of shared substrings.

The same problem comes up if you add STRING-RESIZE!.  I keep going
back and forth on whether or not strings should be the same things as
or a subset buffers vs. making buffers a completely separate type.
(The latter certainly seems to be easier to implement.)


    > Also, there is the possibility on the horizon that we turn
    > string-ref etc into 'primitive generics' which means that people
    > could implement new kinds of strings using GOOPS.

Well, heck.  In that case, maybe consider what I'm planning for Pika
(at least initially).  Purely ASCII strings are stored 1-byte per
character.  Most other strings 2-bytes per character.   Strings using
characters outside the Basic Multilingual Plane, 4 bytes per
character.

You want some fancier-than-libc string functions in C for that -- but
it gives you an expected-case O(1) for STRING-REF and STRING-SET! and
pretty good space efficiency.  It also gives you some performance
glitches as when you store a U+0100 character in an otherwise purely
ASCII 10MB string.  (We're working on providing such fancier-than-libc
functions in libhackerlab -- so they'd be available independently of
Pika if you went this route.)
  
-t



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  reply	other threads:[~2004-01-23 22:18 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-01-16  9:41 Worrying development Roland Orre
2004-01-16 11:59 ` tomas
2004-01-18 21:05 ` Marius Vollmer
2004-01-18 21:58   ` Tom Lord
2004-01-22 21:47     ` Tom Lord
2004-01-22 16:11   ` Dirk Herrmann
2004-01-22 18:42     ` Tom Lord
2004-01-23 11:45       ` Dirk Herrmann
2004-01-23 17:16         ` Tom Lord
2004-01-23 21:01           ` Marius Vollmer
2004-01-23 22:18             ` Tom Lord [this message]
2004-01-24  0:27               ` Marius Vollmer
2004-01-24  0:53                 ` Tom Lord
2004-01-23 22:28             ` Paul Jarc
2004-01-24 12:09               ` rm
2004-01-24 13:29                 ` Marius Vollmer
2004-01-26  2:42                   ` overriding car/cdr (was: Worrying development) Paul Jarc
2004-02-08 16:21                     ` overriding car/cdr Dirk Herrmann
2004-02-08 18:09                     ` Marius Vollmer
2004-02-08 20:56                       ` Paul Jarc
2004-03-20 22:28                         ` Marius Vollmer
2004-03-22 17:05                           ` David Van Horn
2004-03-22 21:03                             ` Marius Vollmer
2004-03-22 17:24                           ` Paul Jarc
2004-01-23 22:37           ` Worrying development Dirk Herrmann
2004-01-23 23:25             ` Tom Lord

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