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Interview: David Roundy of Darcs Revision Control 173

Posted by samzenpus from the what-did-he-say dept.
comforteagle writes "In the aftermath of our last interview with Tom Lord, regardless of personalities, it became apparent that the idea of decentralizing CVS is a big deal. Many mentioned darcs as an alternative to Arch. Mark Stosberg has interviewed project head-hancho David Roundy about darcs, his 'theory of patches,' what's next, and on using Haskell for the project."
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Interview: David Roundy of Darcs Revision Control More

Interview: David Roundy of Darcs Revision Control

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  • Mature RCS? (Score:2, Offtopic)

    by phoenix.bam! ( 642635 )
    When do you move to your own RCS ro support it's own code? Kinda like bootstrapping the RCS? I really have no idea what i mean, but yeah, you get the idea. Did ARCH start out in a CVS somewhere? and where was bitkeeper kept in its infant days?

    • Self-hosting (Score:4, Informative)

      by Earlybird ( 56426 ) <{slashdot} {at} {purefiction.net}> on Thursday November 25, 2004 @01:24AM (#10916375) Homepage
      I believe the term you're looking for is self-hosting. Subversion, for example, was originally maintained in CVS, and has a CVS gateway for maintaining redundant systems.

      For pilot-testing a migration to Darcs, there are scripts available that convert other repository formats (Subversion, CVS, possibly others) into Darcs (and back, actually), so you avoid losing history when making the transition.

    • GNU Arch has hosted itself for a very long time. As far as I know, it has never been publicly hosted in a different RCS. What, if anything, Tom Lord used to host it on his machine before the intial release, you'd have to ask him.

    • Re:Mature RCS? (Score:3, Informative)

      by David Roundy ( 34889 )
      Actually, whether or not an RCS is self-hosting is a pretty useless test of the maturity of that RCS. It is incredibly easy to self-host an RCS, since the users are the developers. Darcs was self-hosting way back before I would even have considered suggesting that anyone else consider using it (as I'm sure was the case with Arch).

      The hard part of writing an RCS is dealing with all those users who do things you never would have thought of, uncovering all sorts of interesting bugs.
  • While "Darcs is written in a Haskell, a functional language that is relatively unknown compared to C or Perl", this really does hurt it's common use. Not being able to get a larger group of developers such as C, C++, or even some interpreted projects means that it becomes one or a few developers working on this project which means fewer patches and additions. A community project will ultimately be the versioning system for community projects. -M

    • Re:Haskell just won't cut it (Score:5, Insightful)

      by QuantumG ( 50515 ) <qg@biodome.org> on Thursday November 25, 2004 @12:26AM (#10916171) Homepage Journal
      So basically you didn't read the article. He gets more developers because it is written in Haskell than he would otherwise because it's one of the few real applications that are written in Haskell - which means if you're someone who just learnt Haskell for the hell of it you've got somewhere to apply those skills.

      • Re:Haskell just won't cut it (Score:5, Interesting)

        by PhYrE2k2 ( 806396 ) on Thursday November 25, 2004 @12:47AM (#10916256)
        I did read the article, however I do DISAGREE with that comment in the article. People won't learn a language for one program, and there is not a large enough body who know the language to really truly UNDERSTAND the program and enough about it to make modifications and additions to it. Compare that to a bunch of C/C++/Java/Perl developers with a massive community body, it's a lot easier to get people to contribute. -M

        • Re:Haskell just won't cut it (Score:5, Informative)

          by cduffy ( 652 ) <charles+slashdot@dyfis.net> on Thursday November 25, 2004 @01:00AM (#10916298)
          Some people will learn a language because they want to know a language that has that specific set of features, regardless of what applications have already been written in that language.

          It's a small group, but if you've the only game in town (in terms of OSS projects for them to work with)... well, that works out pretty well for you!

          No, if Darcs has any major issues, it's the RAM and CPU time requirements, some of which the design makes inherently unresolvable.
          • " Some people will learn a language because they want to know a language that has that specific set of features, regardless of what applications have already been written in that language."

            I learn languages because it's impossible to respond to zealots talking about their language of choice otherwise. It usually works pretty well because zealots of languages nobody knows tend to be used to pontificating at people that don't know anything about the language in question. They're not used to people that can r

            • Re:Haskell just won't cut it (Score:5, Interesting)

              by Pseudonym ( 62607 ) on Thursday November 25, 2004 @01:49AM (#10916454)
              The problem with it is that because it's functional you often end up restructuring half the program for what would have been a trivial change in an imperative language.

              While I don't disagree with this, there are some counter-arguments too:

              • If you find yourself doing that, you may have written your original program in an imperative style in the first place. Alan Holub's argument about getter/setter methods [javaworld.com] applies to declarative programming too. If you wrote in a more language-ideomatic style, you might not be facing a huge restructure at all.
              • Much the same problem can happen in imperative languages, only the class of changes which would trigger such a restructure are different. For example, in a non-GC'd language, you may end up restructuring your program if some critical data lifetime changes. Or, instead of restructuring your program, you might prefer to hack it up instead, making it less maintainable. (It might be argued that languages like Haskell, which discourage this kind of hackery, might be a good thing in the hands of a certain kind of programmer.)
              • Even if you do have to restructure half the program, tools like Haskell's type system make this a less painful task than it would otherwise be.

              Knowing a language also means knowing what kinds of changes are painful and what kinds of changes are not. Knowing this in advance helps you write your programs to be more future-proof.

              • "If you find yourself doing that, you may have written your original program in an imperative style in the first place."

                That wasn't the cause. Naturally, this claim is completely impossible to back up without a protracted debate that would require me to post code. I'm not up for that, so I'm just going to leave this here.

                "Much the same problem can happen in imperative languages, only the class of changes which would trigger such a restructure are different. For example, in a non-GC'd language, you may end

                • That wasn't the cause.

                  Right, hence I said it "may" be the cause. :-)

                  Having said that, your code still might not have been as ideomatic as it could be. For example, what was originally just IO could end up as a huge stack of monad transformers by the time you're done. Making a type synonym for the monad in the first place saves you a lot of hassle down the track.

                  I don't necessarily agree with that.

                  I say this from bitter experience. There is many a time when I've had to thread something through a l

                  • On the other hand, in that situation the compiler isn't working for you. It isn't working against you, either, but a bug found for you is a bug you don't have to track down.

                    This is why I think Boo [codehaus.org] is so damn nifty. It's statically typed, but will infer types if possible (unless the user decides to use the optional explicit typing), and also allows duck typing [codehaus.org] to just resolve everything at runtime Python-style.
                  • "I say this from bitter experience. There is many a time when I've had to thread something through a lot of code, and the compiler found every place where it was needed. No, it wasn't pleasant. But it worked first time."

                    In Python, programs don't tend to involve the degree of recursion that they do in Haskell. Also, it tends to be flatter than Java (eg, you don't end up with subclasses five deep of an abstract class implmenenting some interface), largely because of the dynamic typing and dynamic binding, Ty

            • nested conditionals, well yes, you should use case statements anyway. But then I program in C like a functional programmer anyway to a large extent. Everyone should learn a functional language, just to help you think about things in different ways. And Haskell does have the best type system of any language I have used.
              • "nested conditionals, well yes, you should use case statements anyway."

                Not chained. Nested.

                case statements can be useful in preventing chained conditionals if you're looking at a single value, but they can't really help with nested conditionals.

        • (arguments that Haskell will not cut it because it does not have a large user community)

          I have to say that I am troubled by this kind of attitude, especially on Slashdot. True, open source is mostly about freedom, but it is also about diversity, about innovation, and about trying to do things the right way. Since when do we condemn a project to failure just because it makes a non-mainstream choice, even if the choice was preferred by the developers due to technical superiority?

          How do you feel when PHB

        • Sure, if he wants to get a couple hundred entry-level code grinders in a hurry, if he were a business hiring modular, replaceable Windows monkeys, then Haskell would make his life hard.

          However, neither of the above apply. This is basically a hobbyist project, a rare and rarified subject in both its spheres (version control and Haskell), with considerable overlap between the academic C.S. community that truly understands either.

          "People won't learn a language for one program"? Not even if that program is on
        • When observed facts, based on actual experience, disagree with your theory, obviously the facts must be wrong.
        • People won't learn a language for one program...

          One word: elisp. And thus do I disprove thine assertion:-)

          People will learn a language specifically to use a tool, provided that the cost of learning is less than the value added thereby.

    • Just like how nobody uses CVSup because it's written in Modula-3, right?

    • Re:Haskell just won't cut it (Score:5, Insightful)

      by pnot ( 96038 ) on Thursday November 25, 2004 @12:58AM (#10916291)
      You wrote:
      While "Darcs is written in a Haskell, a functional language that is relatively unknown compared to C or Perl", this really does hurt it's common use.

      How will the choice of language hurt darcs's use? Why on earth would the users of a piece of software care about the language it's written in?

      You wrote:
      Not being able to get a larger group of developers such as C, C++, or even some interpreted projects means that it becomes one or a few developers working on this project

      From the article:
      I've been surprised by the number and quality of contributors darcs has had. There seem to be quite a few people out there just looking for somewhere to use Haskell! :) And in fact, there have also been developers who learned Haskell expressly for the purpose of contributing to darcs. It's such a pleasant language to work with that I think it's more of a draw to developers than a put-off.

      So perhaps you should attempt to assimilate some facts before trotting out your tedious, ill-informed prejudices, hmmm?

      Furthermore, it's not just about the sheer number of developers, it's about the power of the language. A million monkeys writing code are still only monkeys, and the more developers you have on a project, the more co-ordination is required (read Fred Brooks' The Mythical Man-Month if you don't believe me).

      If "number of potential developers" were the only criterion for choosing a project's programming language, everything would be written in BASIC. And Paul Graham makes a good case [paulgraham.com] for coding in less common languages: you'll get people smart enough to learn unusual languages for the hell of it, rather than a mass of monkeys who have little interest in building great software and just want to learn this week's marketable language to improve their employment prospects.
      • Why on earth would the users of a piece of software care about the language it's written in?

        If your users are FOSS developers, they quite likely care about the ability to modify the tool, which includes caring about the languate in which it is written.

        • Re:Haskell just won't cut it (Score:4, Interesting)

          by pnot ( 96038 ) on Thursday November 25, 2004 @02:05AM (#10916507)
          me: Why on earth would the users of a piece of software care about the language it's written in?

          you: If your users are FOSS developers, they quite likely care about the ability to modify the tool, which includes caring about the languate in which it is written.

          Interesting point. Certainly FOSS developers care about being legally allowed to modify code, but I'm not sure that they care, on the whole, about the language.

          emacs, for example, is largely written in elisp -- hardly a mainstream language. Yet it's extremely popular, even among people who don't know any lisp. People who find the need to extend it get a good excuse to learn lisp in a well-motivated, incremental way.

          Speaking personally, I'd be ''more'' inclined to hack on a project written in something interesting like Haskell, ML, Smalltalk, or Lisp. (In fact I chose my current main project partly as an excuse to learn Lisp.) A lot of people like having a motivation for learning a new language, or a practical use for an "academic" language they happen to know. (I learned Haskell in university, so I'd be quite keen to get to use it in the "real world".)

          I think the only time I'd care about the language of a program I'm using would be if it were written in something particularly horrible -- "urgh, if I ever want to modify this I'll have to learn befunge!" But perhaps that's the way some people view Haskell ;-).

          It's a matter of taste, I suppose. I do acknowledge that I'm a bit of a language nut.

          I still maintain that quality is more important than quantity, though. I've been teaching C and Java to second-year undergraduates this year -- having seen some of their code, I can safely say that if I were starting an OSS project, I'd rather have one seasoned Haskell hacker on board than the entire lot of 'em :-).
          • I was about to post more or less the same thing you did -- that users shouldn't care what its written in but I realized as I read your post that it isn't in fact true.

            How would you feel if Microsoft released the source code to MS Excel in, say, Brainf*ck [muppetlabs.com]?

            Actually, lets say its an obscure compiled language that can't be easily translated into another language at all.

            Would you be praising MS for their contribution to the community or decrying their choice of language which limits the legibility and review
            • How would you feel if Microsoft released the source code to MS Excel in, say, Brainf*ck? ... Haskell is completely opaque to me...

              Then it wouldn't be free software: they didn't write it in brainfuck, so a brainfuck release is not a source code release. You could never develop an Excel-sized application in brainfuck.

              I think I addressed your point in my post when I wrote:

              I think the only time I'd care about the language of a program I'm using would be if it were written in something particularly horribl
      • I'm looking at Darcs for possible use in a project, so FWIW here's one data-point on how a potential user would see the Haskell issue. Basically, as a user, I don't care that much. Yeah, it slightly bugged me that I wouldn't be able to understand the code at all (whereas I do think I could at least catch the general drift of something written in Python or Ruby, even though I've never written much more than Hello World in either). But it's such a minor issue. Actually, the bigger thing that's holding me back
      • While "Darcs is written in a Haskell, a functional language that is relatively unknown compared to C or Perl", this really does hurt it's common use.

      I call bullshit. First, the language that a product is written in doesn't hurt use -- it only affects the development process.

      Secondly, what's in a language? I didn't know Haskell until I started looking at Darcs; now I know a bit of Haskell, and soon I hope to be proficient enough to contribute.

      There's something to be said for language agnosticism. Hask

    • Lots of people know how to program in C or Perl to some degree, but you wouldn't want most of them modifying the version control system you are relying on. The pool of capable C or Perl programmer is actually much smaller. And even inexperienced Haskell programmers can do considerably less damage modifying Haskell code than they could modifying C or Perl code.

      Furthermore, darcs doesn't need a "large group of developers", both because it's not a huge system and because it's written in Haskell. Being writ
    • Yes, I think it's safe to discount Darcs because it's written in Haskell, because god forbid not every other C or Perl monkey who can't be bothered to read a language specification for a day won't be able to make their random changes on the system while I'm trying to use it. By your logic, CVS should absolutely be the cat's ass because of all the meaningful contributions coming from the large, trained and expert community of C developers. Or not.

  • CVS-style development with darcs (Score:4, Informative)

    by Ashish Kulkarni ( 454988 ) on Thursday November 25, 2004 @12:23AM (#10916158) Homepage
    There was a good post [abridgegame.org] on this on the mailing list a while ago.

  • Darcs is KISS (Score:5, Informative)

    by Earlybird ( 56426 ) <{slashdot} {at} {purefiction.net}> on Thursday November 25, 2004 @01:11AM (#10916335) Homepage
    Among the plethora of emerging version control systems [zooko.com] -- Subversion, Arch, Monotone and so on -- Darcs stands out for its simplicity and thoughtful design.

    Like CVS, you can get productive within minutes; the same cannot be said for Arch or even Subversion. Let's see:

    john@somewhere$ cd ~/myproject
    john@somewhere$ darcs init

    You now have a Darcs repository! Let's do something with it:

    john@somewhere$ darcs add -r *
    john@somewhere$ darcs record -am "Initial import."
    Finished recording patch 'Initial import.'

    Now your repository contains all your files. Let's look at the changelog:

    john@somewhere$ darcs changes
    Thu Nov 25 06:26:19 CET 2004 johndoe@example.com
    * Initial import.

    Now, where's the server? You need a server to share your repository, right? Nearly -- every repository is a potential server, as long as it's accessible either through the file system, through SSH/SFTP, HTTP or email. Let's go to another machine and check out the repository we just made:

    jane@elsewhere$ darcs get john@somewhere:~/myproject
    Copying patches...
    .
    Finished getting.

    We now have a repository on Jane's box. Let's make a modification:

    jane@elsewhere$ echo "#include <foo.h>" >>foo.c
    jane@elsewhere$ darcs whatsnew --summary
    M ./foo.c +1
    jane@elsewhere$ darcs whatsnew
    {
    hunk ./foo.c 2
    +#include <foo.h>
    }

    This last output, by the way, is Darcs' patch format. A "hunk" is a line-based diff. Other types of changes that may be contained in a changeset include renames, moves and binary changes. (Yes, you can also get a GNU-patch-compatible output similar to "cvs diff".)

    Now let's commit and push the changes back to John's repository:

    jane@elsewhere$ darcs record -am "Added a missing include."
    jane@elsewhere$ darcs push -a
    [...]
    Finished applying...

    Now we can go back to John's machine and look:

    john@somewhere$ darcs changes
    Thu Nov 25 06:26:10 CET 2004 janedoe@example.com
    * Added missing include.

    Thu Nov 25 06:26:19 CET 2004 johndoe@example.com
    * Initial import.

    (Note how Darcs generates a GNU-style changelog for you automatically.)

    Where are the revision numbers, you ask? Well, they don't exist, because they're not needed. Darcs is changeset-oriented, not file-oriented. You can refer to a changeset by name, date, or a special hash identity.

    Darcs changesets aren't just GNU patches; they have context, which means, for example, that someone can check out a repository, move a file "foo.c" into the directory "bar" and commit; meanwhile, another person, working on an older copy of the same repository, edits foo.c (which is still in its old location) and commits that. Darcs know that this edit should apply to foo.c in the new location -- and unlike CVS, you don't need to do anything similar to "cvs update" if you're committing files that have been changed on the server. In other words, people can freely commit changes, and the only kind of visible "conflict" will occur when you actually edit the exact same line.

    Unlike CVS and Subversion, but like Arch and Monotone, Darcs is a distributed version control system. Repositories are islands which are constantly out of sync with each other, and Darcs' patch commutation system takes care of integration the changes that flow between them.

    This system has several extremely useful effects:

    • Offline mode [sourcefrog.net]. You can commit changes even if you're on the road with no access to the server. That's because your own working directory is a repository in its own righ

    • Re:Darcs is KISS (Score:2, Interesting)

      by mindstrm ( 20013 )
      Some nice features there... but you open up with saying "Like CVS, you can get productive within minutes; the same cannot be said for Arch or even Subversion."

      Subversion:

      # Create a local respitory & add files.

      svnadmin create /path/to/repository
      svn import * file://path/to/repository

      I'm really not quite sure how that qualifies as "can't be set up in minutes". Easily as fast as darcs, and very simple.

      The distributed features are what make darcs unique.. it doesn't seem to me to be any fundamentally ea
        • The distributed features are what make darcs unique.. it doesn't seem to me to be any fundamentally easier or faster for basic revision control than subversion, though.

        Subversion seems similarly easy to get started with, but what about repository sharing? To let other people access your repository, you must set up a server of some kind, be it WebDAV, or svnserve -- although I'm sure Subversion must support something like an "ssh://" protocol.

        • Yup.

          svn co svn+ssh://user@host/path/to/repo repo

          will check out a repository, tunnelled over ssh. No need to run a subversion server to do that.

          One of the nice things about subversion (recently converted user, very happy so far) is the support for multiple url formats and communications methods.

          Another notable thing (for windows users) is TortoiseSVN, (an explorer shell extension) which is just great.

          I can see how the distributed, multi-repo model of bitkeeper/darcs/arch is superior but svn looks good i

          • Re:Darcs is KISS (Score:5, Interesting)

            by Earlybird ( 56426 ) <{slashdot} {at} {purefiction.net}> on Thursday November 25, 2004 @03:53AM (#10916845) Homepage
            • One of the nice things about subversion (recently converted user, very happy so far) is the support for multiple url formats and communications methods.

            Darcs and Arch both have this. (Arch undoubtedly has the most extensive protocol support of any revision control system.)

            • Another notable thing (for windows users) is TortoiseSVN, (an explorer shell extension) which is just great.

            Tortoise is quite nice indeed -- I used TortoiseCVS for years.

            • I can see how the distributed, multi-repo model of bitkeeper/darcs/arch is superior but svn looks good if you only need single-repo.

            Need is just one aspect of the development process; right now CVS gives most people what they need, despite the cracks in the lacquer. Darcs doesn't just erase the cracks, but improves the process.

            For example, I occasionally submit patches to certain open-source projects. The easiest way to do this is to check out the CVS repository, make my changes, and do "cvs diff -u" to get the patches in that format, which I tend post to some Bugzilla server or email to somebody. But I can't commit them. I don't mean to the master repository -- I mean locally. There's no way I can bundle my file patches in a changeset and keep its history. I'm basically managing a CVS working directory where my changes are never checked in.

            With Darcs, I just do "darcs get" to get the master repository, make my changes, commit them locally. I can use "darcs send" to submit my changes to the project maintainer. Anyone else can grab my patches with "darcs get" or "darcs pull". I can be Alan Cox to some Linus without breaking my back over patch management.

      • "The distributed features are what make darcs unique.."

        Hardly, as it is the defining feature of BitKeeper and GNU Arch. It's a very good idea, however.
    • Wow... This looks so much simpler even than CVS, especially as soon as things get hairy with parallel development.

      Perfect sales pitch! I'll have to "check it out" now, guess I should say "whatsnew it" instead! :)
    • Your comment would still be correct if I changed every occurence of "darcs" with "arch" (except for the command lines, of course).

      So, what's the difference between Arch and Darcs?

      • Here: (Score:3, Informative)

        by warrax_666 ( 144623 )
        I think you may find this page [berlios.de] interesting.

        Major differences:
        1. Darcs is must less strict: For example, it doesn't have a built-in concept of branches/versions (which is necessary in Arch because of the patch ordering/application constraints).
        2. All working directories are repositories themselves. This can be very useful (for example, it makes it trivial to manage /etc using darcs), but also somewhat dangerous.
        3. Interactive approval of every recorded diff chunk (change). This may not sound like a big deal, but
        • going by that page, subversion looks like a better deal than darcs.
          • I fail to see how. It isn't strictly superior in all categories, and there are certainly some significant differences which would make either (but not both) viable in certain scenarios.

            Disclaimer: I'm currently using Arch for all my repos, but that's mainly because Haskell is not really supported properly on my architecture (by my distro). Yet.
            • 1) Subversion doesnt use haskell
              2) File and Directories Copies (big feature!)
              3) Repository Permissions
              4) Ability to Work only on One Directory of the Repository (svn is much more flexible in this regard)
              5) Availability of Graphical User-Interfaces.

              the cvs-ish syntax is also a plus.
                • 1) Subversion doesnt use haskell

                How does this affect users?

                • 2) File and Directories Copies (big feature!)

                It's a big feature because it underlies Darcs' branching support. Darcs doesn't have a command to copy something within the repository; rather, you copy the entire repository.

                • 3) Repository Permissions

                Do you use them? Most people don't, as far as I know.

                • 4) Ability to Work only on One Directory of the Repository (svn is much more flexible in this regard)

                Agreed.

                • 5) Availability of Graphic
                • svn syntax is exactly the same as cvs for those:

                  svn init -- cvs init
                  svn checkout -- cvs checkout
                  svn update -- cvs update
                  svn commit -- cvs commit
                  svn diff -- cvs diff
                  svn log -- cvs log

                  its nice to have the same syntax, especially when youre working on multiple opensource projects using a mix of cvs and svn. (where the repositories arent under your control, youre just a developer)
                  • its nice to have the same syntax

                    Only if the semantics are the same. If the semantics differ (subtly) it's not a good thing. Besides, you still haven't shown your original claim (that svn is strictly superior to darcs). Yes, svn is superior to darcs in some ways, but darcs is also superior to svn in some regards.

        • Re:Here: (Score:4, Interesting)

          by boa13 ( 548222 ) on Thursday November 25, 2004 @06:13AM (#10917190) Homepage Journal
          One important feature is missing from the page:

          Support for signing patches and archives

          Allows to verify who created/commited the patches. Allows to verify the integrity of a repository in case of compromise.

          * Arch: Excellent. Each patch can be signed, repositories can be fully verified.
          * Darcs: Incomplete. Patches sent by email can be signed so the recipient can verify the identity of the submitter. No support for verifying repository integrity. [1]
          * Subversion: N/A

          [1] Problem is: You can only sign something that will not vary once distributed, Darcs patches vary once distributed.
          • I suspect your footnote is incorrect (although it been a long time since I looked at darcs and may remember incorrectly). IIRC, the patches themselves don't vary once distributed, just the ordering of them, so it should be possible to sign individual changes. Of course, this isn't nearly enough to verify repository integrity/authenticity, but I think something could be added relatively easily.
            • Patches themselves do vary at least when a merger patch is needed (conflict). But this could be stored as a patch to the patch. It might even be possible to verify that the stored changes are correct.

            • No, I'm afraid the footnote is dead on. When patches are commuted their content changes, although their meaning remains the same. This happens when people pull (or push) patches from one repository to another.

              There is an idea, a repository of patch bundles, which could allow signed patches to be kept, at the cost of either duplication of information or inefficiency. It would "just need to be implemented." It would be a bit tedious, but is simple enough that it could be done (terribly inefficiently) usi
      • The only problem with Arch is that while the implementation might be KISS, the user interface is not and its almost impossible to map a good old CVS-users workflow onto Arch.

        • Your comment would still be correct if I changed every occurence of "darcs" with "arch" (except for the command lines, of course).

        Not quite. Arch isn't simple to use.

        • So, what's the difference between Arch and Darcs?

        From the perspective of a Darcs user:

        Darcs is much simpler to use.

        Darcs doesn't have branches, because every repository is conceptually a branch.

        Darcs' patch format is just text (Arch uses a tarball).

        Darcs has no notion of persistent file identity (which I consider a plus).

        Darc

    • john@somewhere$ cd ~/myproject
      john@somewhere$ mkdir RCS

      You now have an RCS repository! Let's do something with it:

      john@somewhere$ ci -u -t-FirstPost *

      Now your repository contains all your files.

      Oh, wait, rcs is old and uncool...
        • Oh, wait, rcs is old and uncool...

        If you had tried to duplicate the other steps in my little tutorial, you would have seen why RCS doesn't cut it. RCS isn't a distributed system.

        • If you want either a centralized, or a distributed system, then use CVS - there is even a version of CVS that works via email. If you want a simple system, then use RCS. If you want a wide choice of client programs, then use CVS. Note that RCS is contained in CVS.

          I'm not a CVS fanatic, not at all, but I am seeing many people recreating the features of CVS with great effort, while all they really need is a better client.

          The CVS server doesn't matter, it works, it is debugged, it is reliable, there reall

  • Its the clients and API that matter (Score:3, Informative)

    by monkeyboy87 ( 619098 ) on Thursday November 25, 2004 @01:49AM (#10916456)
    no matter what the change set "theory" are implemented into the product if it's not easy to do things with it, it will languish. VSS and CVS are still used widely becuase there are lots of clients and tools that make it useful. the draw of SVN (loved or hated) is that it has a good client and the command line client is easy to drive with scripting tools

  • Interesting app. non-troll questions (Score:3, Interesting)

    by mattr ( 78516 ) <<mattr> <at> <telebody.com>> on Thursday November 25, 2004 @01:51AM (#10916466) Homepage Journal
    The previous poster who showed how easy it is to use darcs sold me, I am thinking it could be real useful
    right away just for my own work.

    Took a brief look at the pretty site. Personally I've been intrigued by Haskell for a while though never jumped in, and I use Perl. My questions:

    1. Can the elegant quantum reality inspired code be separated off? Though my take is that it is already separate, as a Haskell function.. the reason for the question is that it sounds like it would be useful for a whole lot of things. Instead of implementing app/protocol X over darcs, I am wondering if you could include an (inline) Haskell module in a Perl app that would do the rest.

    1.5 ..or is there another way to access the Haskell theory of patches functionality from outside the app?

    2. Next question, can Haskell be embedded inline in Perl code?

    3. Can the quantum theory of patches be implemented as a Perl module, and ignoring the probably truth that anything not Haskell will not be as elegant as Haskell, would such an implementation benefit/be renedered possible by using the Perl functional or Quantum:: modules?

    3.5 At risk of a flame war I'd love to use this in XEmacs. Anybody? This post written in vim so no flames please!

    4. Reading about the symmetry or lack of it, concepts of physics this is helping me think about an app of my own. I'd like to read more about this does anyone have links?

    5. Time to learn Haskell!! Great!

    • I can't answer all of your questions. The mailing list [abridgegame.org] would be the place to ask.
      • 2. Next question, can Haskell be embedded inline in Perl code?

      Not that I'm aware. However, all you need is an embeddable Haskell interpreter. I believe this is possible with Hugs [haskell.org], which has a "server interface [haskell.org]", and possibly even with ghc [haskell.org] (the native compiler that Darcs is compiled with). You'd probably have to write the C/Perl interface yourself.

      • 3. Can the quantum theory of patches be implemented as a Perl module ...
      • 3.5 At risk of a flame war I'd love to use this in XEmacs. Anybody? This post written in vim so no flames please!

      This may be useful [scannedinavian.org]

      • Excellent link. Thank you very much! I also note belatedly that there is a link in the wiki about an emacs mode.

        I don't know why they have marked my last two serious questions in threads as trolls, especially when I say this is not a troll. Is there a filter that makes everyone who says that a troll?? Sheesh. Of course if this reply is marked as a troll too then we know..

    • Re:Interesting app. non-troll questions (Score:5, Informative)

      by David Roundy ( 34889 ) on Thursday November 25, 2004 @08:06AM (#10917486) Homepage
      1. It's actually hard to use the patch commutation code to do any good outside the concept of a darcs repository.

      1.5 I've thought about creating a C library for manipulating/querying darcs repositories, but haven't gotten around to it. The hard part would be of course designing the API. Ideally I'd like the interface to be such that programs using the library couldn't accidentally corrupt the repository.

      2. Darcs requires ghc, since it uses some library code only available in ghc to do more efficient IO, string manipulation and to access zlib. It turns out to be a pain on many systems to link with the necesary libaries when using the interpereted version of ghc. So probably accessing darcs from perl will have to go through the executable until a C library is written (which could of course have perl bindings).

      3. Rewriting darcs in perl (or parts of it) would be possible, but would be a pain. In particular, the commutation of patches which have conflicts is pretty complicated.
      • Thank you *very* much for your responses!!

        I'll definitely study the wiki. I'm interested in using darcs as darcs, and also in the theory and how it came out of quantum reality concepts. I'm not about to write darcs in perl, but was intrigued with the possibility of accessing the theory side in perl for other applications than strictly controlling patches of source code for developers. Probably it would be more helpful to learn about how you came up with the theory itself than to actually try to implemen

  • Needs wider adoption (Score:5, Interesting)

    by haeger ( 85819 ) on Thursday November 25, 2004 @02:07AM (#10916514)
    While darcs is nice it needs wider adoption. When it comes to a project that people are working on, you have almost as many boxes as you have developers and for a revision control program to be adopted and used there has to be binaries for all those devels. AFAIR there are some issues with the win32 binary? One of our devels had major problems with it and now we're living with both a cvs and a darcs repository, and noone really knows where to send patches. I think it's safe to say that our project is dying, if not dead already.

    Not that I blame darcs or anything, just that one need to be sure that darcs work for everyone before commiting to it. CVS works on all platforms and is well tested. Darcs will hopefully get there.

    And yes, I did my part and created a package for my platform. It's linked from the binary download page.

    .haeger

    • Re:Needs wider adoption (Score:2, Insightful)

      by Anonymous Coward
      CVS works on all platforms
      ... for an appropriate definition of "works".

      CVS doesn't have atomic check-in, it's directory handling is crap, etc. etc. Still, like you said, it's probably still the best bet if you want to do development on both UNIX and Win32, although Subversion(!) is catching up fast.
  • It seems to me that a LOT of people in these comments are remarking that David's choice of Haskell makes darcs a no-go. I would make this comment:

    If someone told you to use <Tool X> for a project, you would say, "No way, <Tool Y> is more suitable for this job, and it's what I want to use." (substitute X and Y with whatever - C/Java/Perl/VB - you want).

    I think David chose what he felt was the best tool for the job, taking the problem-to-solve and his own expertise into consideration. In the lig

  • Our experience CVS vs. DARCs (Score:5, Informative)

    by ites ( 600337 ) on Thursday November 25, 2004 @05:29AM (#10917081) Journal
    We are looking at something to replace our ageing CVS system. We have large OSS projects, worked on by teams of 3-10 people. CVS is very good for what it does but we are feeling its limitations. The biggest problems are that forks are too delicate to use, so we don't use them, and that in order to work you need access to the central archive.

    Darcs looked like the best choice. We converted and imported some of our archives. Then we tried checking them out. With CVS, 2-3 minutes. With darcs, 30 minutes.

    Our conclusion: darcs is not scalable. Admittedly our code base is large and has a huge history, but in order to use darcs we would have had to break our projects into many small pieces, each with their own repository.

    Darcs looks good. But it needs to be made much, much faster if it's to work with large projects.
    • ...why not make the jump to a system meant to replace CVS's centralized model, such as subversion. Forks are very easy to do, truly atomic commits, CVS to SVN repository converter, similar command line params to CVS etc. etc.

      Our current repo is 9 gigs and works beautifully.
    • you might want to try subversion?
    • Is it because Haskell is an interpeted language, or it is a design fault? I doubt it is the language, but I thought to cover that base too.

    • Re:Our experience CVS vs. DARCs (Score:5, Informative)

      by David Roundy ( 34889 ) on Thursday November 25, 2004 @07:53AM (#10917441) Homepage
      Darcs get (equivalent to CVS checkout) is the single least efficient command in darcs. People keep telling me I need to fix this, since it's the first thing users see, but it's really not an important command to optimize (apart from first impressions issues). When run locally (to create a new branch) it's fast.

      And comparing darcs get with cvs checkout really isn't fair, since darcs gives you a copy of the full history of the repository, a separate branch on which to record changes before committing them to the centralized repository, and the ability to browse the history offline.

      If you want a fast get, just run optimize --checkpoint on the parent repository (assuming you've tagged recently--if not, then tag the current state first), and then use the --partial flag when running darcs get. It'll still give you more flexibility than a cvs checkout, and will be much faster.

      • "Darcs get (equivalent to CVS checkout) is the single least efficient command in darcs. ... And comparing darcs get with cvs checkout really isn't fair.."


        You've lost me, unfortunately. Darcs does seem, in some ways, to be fantastically simple, but your explanation of how to do the real equivalent of a cvs checkout just sounds irritating.
      • So why don't you make 'darcs get' use --partial by default, and require 'darcs get --all' to get the full history? Since most people will be familiar with 'cvs checkout' and a couple of people with 'tla get,' both of which get only the current version, it seems reasonable to me to make the default what people expect -- with the speed that people expect?

        I like having the full history, but I think that in the usual case "check out the current version in 3 minutes" is a more reasonable default than "check ou

  • How would decentralizing CVS be an improvement? CVS utilities can already work in both RCS and CVS modes.

  • Patches applied out of order - freedom or folly? (Score:2, Interesting)

    by Anonymous Coward
    Having designed,implemented and supported an enterprise-wide (1200+ user) Configuration Management services for over 3 years, I find that the number one thing that most developers want is version control that STAYS OUT OF THE WAY. They DON'T want every bell and whistle. They have to concentrate on their code, not some "neat" (or read pain in the a$$) way to do something.

    I support ClearCase/ClearQuest worldwide for a large corp. I deal with the helpdesk calls, the support, the engineering efforts the "best
  • I played around with several source control systems a while back; I like Darcs, it was the easiest of the distributed systems to understand, with a concise and easy-to-understand command-line interface.

    But in the end I think a centralized repository is right for many (most?) projects: Why Bitkeeper Isn't Right For Free Software [mit.edu] (by Greg Hudson) was the most convincing argument to me.

    Of course, you can simulate a centralized model with a distributed system (just don't use the distributed bits), but it seems like you are on your own at that point. Subversion is behind when you compare distributed features (of course), but when you compare the other features (usability, access via various method, programmatic access, etc), it's way ahead. As it would be; centralized systems are easier to think about, so they are easier to develop with and on top of.

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