Darcs
Encyclopedia
Darcs is a distributed revision control
system created by David Roundy
; it was designed to replace traditional, centralized source control systems such as CVS
and Subversion. Key features include the ability to choose which changes to accept from other repositories, interaction with either other local (on-disk) repositories or remote repositories via SSH
, HTTP, or email, and an unusually interactive interface. The developers also emphasize the use of advanced software tools for verifying correctness: the expressive type system of the functional programming language Haskell
enforces some properties, and randomized testing via QuickCheck
verifies many others. The name is usually sentence-cased, and is a recursive acronym
for Darcs Advanced Revision Control System.
software, which allows the user to view a source tree history as series of snapshots going back in time, a darcs source tree is modelled as a set of patches, where each patch is not necessarily ordered with respect to other patches i.e. the set of patches is only a partially ordered set
. A particular version of the source tree corresponds to a particular set of patches; this set of patches may or may not have existed at some other point in time.
in June 2002. These discussions didn't lead to any code being committed to arch, but did lead to his theory of patches. After writing an initial version of darcs in C++
, the Haskell
version was written in Autumn 2002 and released to the public in April 2003.
Version 2.5 contains many improvements over the 2.4 series. Most notable are the performance improvements in
to prove the correctness of some of its aspects. Camp remains close to the Darcs project and the authors expect the two projects to merge again once Camp is more mature.
Distributed revision control
A distributed revision control system , distributed version control or decentralized version control keeps track of software revisions and allows many developers to work on a given project without necessarily being connected to a common network.-Distributed vs...
system created by David Roundy
David Roundy
David Roundy is a physicist known primarily as the author of the darcs version control system.His parents are Virginia Roundy & Willard Roundy. He obtained a B.A. in Physics and Chemistry in 1995 and a Ph.D. in physics from Berkeley in 2001. Between 2001 and 2006 he did postdoctoral work at MIT...
; it was designed to replace traditional, centralized source control systems such as CVS
Concurrent Versions System
The Concurrent Versions System , also known as the Concurrent Versioning System, is a client-server free software revision control system in the field of software development. Version control system software keeps track of all work and all changes in a set of files, and allows several developers ...
and Subversion. Key features include the ability to choose which changes to accept from other repositories, interaction with either other local (on-disk) repositories or remote repositories via SSH
Secure Shell
Secure Shell is a network protocol for secure data communication, remote shell services or command execution and other secure network services between two networked computers that it connects via a secure channel over an insecure network: a server and a client...
, HTTP, or email, and an unusually interactive interface. The developers also emphasize the use of advanced software tools for verifying correctness: the expressive type system of the functional programming language Haskell
Haskell (programming language)
Haskell is a standardized, general-purpose purely functional programming language, with non-strict semantics and strong static typing. It is named after logician Haskell Curry. In Haskell, "a function is a first-class citizen" of the programming language. As a functional programming language, the...
enforces some properties, and randomized testing via QuickCheck
QuickCheck
QuickCheck is a combinator library written in Haskell, designed to assist in software testing by generating test cases for test suites. It is compatible with the GHC compiler and the Hugs interpreter....
verifies many others. The name is usually sentence-cased, and is a recursive acronym
Recursive acronym
A recursive acronym is an acronym or initialism that refers to itself in the expression for which it stands...
for Darcs Advanced Revision Control System.
Model
Unlike most SCMSoftware configuration management
In software engineering, software configuration management is the task of tracking and controlling changes in the software. Configuration management practices include revision control and the establishment of baselines....
software, which allows the user to view a source tree history as series of snapshots going back in time, a darcs source tree is modelled as a set of patches, where each patch is not necessarily ordered with respect to other patches i.e. the set of patches is only a partially ordered set
Partially ordered set
In mathematics, especially order theory, a partially ordered set formalizes and generalizes the intuitive concept of an ordering, sequencing, or arrangement of the elements of a set. A poset consists of a set together with a binary relation that indicates that, for certain pairs of elements in the...
. A particular version of the source tree corresponds to a particular set of patches; this set of patches may or may not have existed at some other point in time.
Shortcomings
Darcs has been criticized on the grounds of performance. The worst of these issues was the Darcs 1.x merge algorithm that, in the worst case, could do exponential work to merge some conflicts. Although the issue was not completely corrected in Darcs 2, exponential merges have been minimized. Unfortunately, bugs still remain in which the merging of recursive conflicts fails.History
Darcs evolved out of David Roundy's efforts to design a new patch format for GNU archGNU arch
In computing, GNU arch is a distributed revision control system that is part of the GNU Project and licensed under the GNU General Public License...
in June 2002. These discussions didn't lead to any code being committed to arch, but did lead to his theory of patches. After writing an initial version of darcs in C++
C++
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
, the Haskell
Haskell (programming language)
Haskell is a standardized, general-purpose purely functional programming language, with non-strict semantics and strong static typing. It is named after logician Haskell Curry. In Haskell, "a function is a first-class citizen" of the programming language. As a functional programming language, the...
version was written in Autumn 2002 and released to the public in April 2003.
Version 2.5 contains many improvements over the 2.4 series. Most notable are the performance improvements in
record and pull and the --bisect option for trackdown.Related
A related project called Camp ("Commute and merge patches") attempts to develop Darcs's patch algebra more formally, including the use of CoqCoq
In computer science, Coq is an interactive theorem prover. It allows the expression of mathematical assertions, mechanically checks proofs of these assertions, helps to find formal proofs, and extracts a certified program from the constructive proof of its formal specification...
to prove the correctness of some of its aspects. Camp remains close to the Darcs project and the authors expect the two projects to merge again once Camp is more mature.
External links
- Darcs manual
- Darcs wiki - (PDFPortable Document FormatPortable Document Format is an open standard for document exchange. This file format, created by Adobe Systems in 1993, is used for representing documents in a manner independent of application software, hardware, and operating systems....
) - Interview with darcs' creator on its origins and ideas
- darcsweb Tool to serve darcs repositories via [HTTP]
- An Algebra of Patches, Ian Lynagh, October 30, 2006
- What makes Camp and Darcs unique? Video presentation.
- Patch-Tag: Project Hosting for Darcs
- Darcs Den: Project Hosting for Darcs