Groups > comp.lang.java.programmer > #9580

Re: Immutable Datastructures with good Sharing

Date	2011-11-05 10:55 -0700
From	Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com>
Newsgroups	comp.lang.java.programmer
Subject	Re: Immutable Datastructures with good Sharing
References	<j9292v$f69$1@news.albasani.net> <stack-20111105042359@ram.dialup.fu-berlin.de> <j937eq$7k4$1@news.albasani.net> <4839047.311.1320512815263.JavaMail.geo-discussion-forums@pref15>
Message-ID	<24CdnZZfrM8C5SjTnZ2dnUVZ_qmdnZ2d@posted.palinacquisition> (permalink)

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On 11/5/11 10:06 AM, Lew wrote:
> Jan Burse wrote:
>> Stefan Ram schrieb:
>>>     However, in computer science, a stack is well known as a
>>>     specific mutable entity with specific performance
>>>     properties. So, an »immutable stack« should not be called
>>>     »stack«.
>>
>> If you take the subdomain of functional programming
>> in computer science, the people there wouldn't
>> probably agree. A stack can be viewed as an abstract
>> datatype:
>>
>>      push : Stack x Element ->  Stack
>>      pop : Stack ->  Stack x Element | Fault
>>
>> By the above one would loose the possibility to directly
>> reference a stack by one process. And then see what
>> an another process is doing on it.
>
> Your answer does not speak to the inherent contradiction in the term "immutable stack".

What inherent contradiction?  Please cite an authoritative reference 
that requires that the data structure known simply as a "stack" must be 
implemented using mutable instances.

Requiring mutable instances would mean one could not, for example, 
implement a stack at all in languages like Lisp or XSLT.  Yet having 
done so in both, I find that assertion obviously wrong.

The key to a "stack" is that it orders elements such that there are two 
operations, one to add an element and one to remove an element, and 
those added most recently are removed most recently.  That's all.  In a 
language like Lisp, you don't even need a specialized data structure for 
that; it comes free with the language.

There's nothing about that definition that requires a given instance of 
"stack" to be mutable, any more than having an "int" that allows 
operations such as addition or subtraction requires any given "int" 
instance to be mutable, nor any more than having a "String" that allows 
operations such as concatenation and substring requires any given 
"String" instance to be mutable.

Finally, if the above does not persuade, please let us know: what shall 
we call a data structure that works just like a stack but which uses 
immutable instances, if not a "stack"?  What word do you think is more 
appropriate than "stack" and will communicate the basic nature of the 
data structure in a more efficient, obvious way than the word "stack"?

It's funny.  I realize that in this newsgroup, so many threads devolve 
into this sort of pointless (and usually wrong) criticism of 
terminology.  But here's a relevant discussion that occurred in the 
context of a .NET-related blog, with four pages of comments, and not 
once did anyone stoop to distracting from the real point of the 
discussion to question the use of the word "stack" to describe the data 
structure:
http://blogs.msdn.com/b/ericlippert/archive/2007/12/04/immutability-in-c-part-two-a-simple-immutable-stack.aspx

Quite a contrast.

(By the way, Eric has lots of other good stuff on the topic of 
immutability. See here 
http://blogs.msdn.com/b/ericlippert/archive/tags/immutability/ if you're 
interested in productive reading on the topic, albeit in the context of 
.NET rather than Java).

Pete

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Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 04:03 +0100
  Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 12:42 +0100
    Re: Immutable Datastructures with good Sharing markspace <-@.> - 2011-11-05 09:35 -0700
      Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 19:33 +0100
        Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 14:42 -0400
          Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 19:52 +0100
            Re: Immutable Datastructures with good Sharing Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-11-05 19:32 +0000
            Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 15:31 -0400
              Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 20:50 +0100
                Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 16:26 -0400
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 21:35 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 21:38 +0100
                Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 16:59 -0400
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 22:06 +0100
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-05 16:41 -0400
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 21:42 +0100
                Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 17:11 -0400
            Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-05 16:20 -0400
              Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 21:33 +0100
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-05 16:38 -0400
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 21:41 +0100
                Re: Immutable Datastructures with good Sharing markspace <-@.> - 2011-11-05 17:20 -0700
                Re: Immutable Datastructures with good Sharing Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-11-05 22:13 -0300
                Re: Immutable Datastructures with good Sharing markspace <-@.> - 2011-11-05 20:05 -0700
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 10:27 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 10:14 +0100
    Re: Immutable Datastructures with good Sharing Lew <lewbloch@gmail.com> - 2011-11-05 10:06 -0700
      Re: Immutable Datastructures with good Sharing Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-11-05 10:55 -0700
        Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 19:30 +0100
          Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 18:16 -0400
            Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 23:20 +0100
            Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 23:38 +0100
        Re: Immutable Datastructures with good Sharing Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-11-05 17:47 -0300
        Re: Immutable Datastructures with good Sharing Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-11-05 14:26 -0700
      Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-05 16:14 -0400
  Re: Immutable Datastructures with good Sharing Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-11-05 14:35 -0700
    Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 22:42 +0100
      Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 22:50 +0100
      Re: Immutable Datastructures with good Sharing Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-11-05 14:51 -0700
        Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 22:58 +0100
          Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 23:03 +0100
            Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 23:07 +0100
            Re: Immutable Datastructures with good Sharing Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-11-06 09:44 +0200
              Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 10:22 +0100
                Re: Immutable Datastructures with good Sharing Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-11-06 09:05 -0400
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 14:16 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 14:22 +0100
                Re: Immutable Datastructures with good Sharing Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-11-06 14:30 +0000
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 16:02 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 16:08 +0100
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-06 16:18 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 16:54 +0100
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-06 17:31 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 22:33 +0100
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-06 16:47 -0500
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 16:58 +0100
                Re: Immutable Datastructures with good Sharing Tom Anderson <twic@urchin.earth.li> - 2011-11-07 01:01 +0000
                Re: Immutable Datastructures with good Sharing Lew <lewbloch@gmail.com> - 2011-11-06 17:26 -0800
                Re: Immutable Datastructures with good Sharing Tom Anderson <twic@urchin.earth.li> - 2011-11-07 23:45 +0000
                Re: Immutable Datastructures with good Sharing Lew <lewbloch@gmail.com> - 2011-11-06 14:44 -0800
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-06 17:51 -0500
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 01:28 +0100
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-06 19:50 -0500
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 02:13 +0100
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-06 20:20 -0500
                Re: Immutable Datastructures with good Sharing Lew <lewbloch@gmail.com> - 2011-11-06 17:29 -0800
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 11:22 +0100
                Re: Immutable Datastructures with good Sharing Tom Anderson <twic@urchin.earth.li> - 2011-11-06 23:02 +0000
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 00:32 +0100
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 01:10 +0100
                Re: Immutable Datastructures with good Sharing Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-11-07 10:24 +0000
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 11:52 +0100
                Re: Immutable Datastructures with good Sharing Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-11-07 11:12 +0000
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-07 17:24 -0500
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 02:08 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 05:03 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 05:13 +0100
                Re: Immutable Datastructures with good Sharing Tom Anderson <twic@urchin.earth.li> - 2011-11-07 23:38 +0000
                Re: Immutable Datastructures with good Sharing Tom Anderson <twic@urchin.earth.li> - 2011-11-09 22:06 +0000
                Re: Immutable Datastructures with good Sharing Gene Wirchenko <genew@ocis.net> - 2011-11-09 18:02 -0800
  Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 00:28 +0100
    Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 00:39 +0100
      Re: Immutable Datastructures with good Sharing Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-11-06 20:57 -0400
        Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 04:58 +0100
          Re: Immutable Datastructures with good Sharing Silvio Bierman <silvio@moc.com> - 2011-11-07 15:13 +0100
            Re: Immutable Datastructures with good Sharing Cthun <cthun_202@qmail.net.au> - 2011-11-07 12:54 -0500
              Re: Immutable Datastructures with good Sharing "B1ll Gat3s" <wm.g4t3s@m1cr0s0f7.c0m> - 2011-11-07 18:07 -0500
                Re: Immutable Datastructures with good Sharing B1ll Gat3s <wm.g4t3s@m1cr0s0f7.c0m> - 2011-11-07 22:07 -0500
                Re: Immutable Datastructures with good Sharing "B1ll Gat3s" <wm.g4t3s@m1cr0s0f7.c0m> - 2011-11-08 00:17 -0500
                Re: Immutable Datastructures with good Sharing thoolen <th00len@th0lenbot.thorium> - 2011-11-08 16:03 -0500
                Re: Immutable Datastructures with good Sharing Cthun <cthun_202@qmail.net.au> - 2011-11-08 15:49 -0500
                Re: Immutable Datastructures with good Sharing "B1ll Gat3s" <wm.g4t3s@m1cr0s0f7.c0m> - 2011-11-08 18:01 -0500
                Re: Immutable Datastructures with good Sharing thoolen <th00len@th0lenbot.thorium> - 2011-11-08 20:46 -0500
                Re: Immutable Datastructures with good Sharing "Cthun" <cthun_202@qmail.net.au> - 2011-11-08 22:43 -0500
                Re: Immutable Datastructures with good Sharing thoolen <th00len@th0lenbot.thorium> - 2011-11-09 08:28 -0500
                Re: Immutable Datastructures with good Sharing thoolen <th00len@th0lenbot.thorium> - 2011-11-08 16:00 -0500
  Re: Immutable Datastructures with good Sharing Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-11-07 08:46 -0800

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