Darcs is a free, open source revision control system along the lines of cvs or arch. One thing we can do to help is to improve the darcs code base to the point where shifting to a new patch theory, or a new repository format, or a new set of primitive patches is relatively smooth and easy. A patch is defined by a representation, together with a set of rules for how it behaves which it has in common with its patch type. Understanding darcspatch theory wikibooks, open books. We do not describe exactly the theory that darcs 2 is built on, as it is known to have some problems, but our theory is similar to darcs 2s.
The theory of change is based on the fundamental logic that a road can provide access to markets as well as allow for the provision of security, which in turn can lead to improved incomes and security for the population of north and south kivu. In this paper, we show how patch theory in the style of the darcs version control system can be developed in homotopy type theory. The darcs patch formalism is the underlying math which helps us understand how darcs should behave when exchanging patches between repositories. Conflict marking confusion when pulling a deleted file with darcs. We reformulate patch theory using the tools of homotopy type theory, and clearly separate formal theories of patches from their interpretation in terms of basic revi. In very general terms, donors, foundations and policylevel organisations and departments tend to work with highlevel theories of. Darcs is a distributed version control system based on a unique algebra of patches called patch theory.
Git was considerably worse than darcs, and it still isnt nearly as userfriendly, but on the other hand, ive never lost any productivity time to git bugs. The implementation has some serious issues however. And actually, git users often reason in terms of patches, displaying commits as. In the meantime, there is a ton of work we can do to prepare the ground for it. If you want to do a similar change with a different starting snapshot, you need to patch. In revision control software, a changeset is a set of changes which should be treated as an indivisible group i.
My confusion arises from the following statement taken from here. These calculations implement a socalled patch theory. This post is intended for people interested in patch theory and its implementation in darcs. Analysis, modeling and testing of darcs patch theory kernel. Patch theory was originally described informally by david roundy and the formalisation of darcs basis continue to be an unresolved topic nowadays, which keeps open the question of darcs reliability since it may fail in some corner cases. Darcs automatically calculates whether patches can be reordered an operation called commutation, and how to do it. Darcs patch theory more or less ian lynagh september 7, 2008 1 overview in this document we present a description of a darcslike patch theory. Theory of change is unlikely to be a tool that you use in isolation. I should start by saying that i have obviously drawn a lot of ideas and inspiration from darcs, and especially. Darcs patch theory is centered around patches, with two primitive operations, commutation and inversion. A formalization of darcs patch theory using inverse semigroups. The patch p below modifies repository from state s to state e. A passing familiarity with patches, contexts, inverses, etc is useful, but not required, as we restate some basic definitions in this section.
When arjan records this change adding beer, we produce a patch which tells us not only what. Its main innovation compared to darcs is to use a better data structure for its pristine, allowing for. Apr 17, 2011 with darcs a change in b1 will change the result. Categories for the working mathematician, volume 5 of graduate texts in mathematics. A categorical theory of patches samuel mimram and cinzia di giusto cea, list abstract when working with distant collaborators on the same documents, one often uses a version control system, which is a program tracking the history of files and helping importing modifications brought by others as patches. In order to manipulate changes, darcs stores each change using a patch. Compared to this, pijuls theory revolves around files i. Darcs is decentralized, based on a theory of patches with roots in quantum mechanics. Understanding darcspatch theory wikibooks, open books for an. This is a change in workflow which is much beloved by almost all longtime darcs users it means you can opportunistically make an unrelated change as you are working on a different. The patch itself is not changed, since it describes a single change, which must be the same regardless of its representation a. Basic patches describe the change between the states. Im curious to know why doesnt git rebase take exponential time. Its not even really about patch theory, because im too lazy to read through the actual article on patch theory in enough detail what this really is is a nice way to finish off my series of articles on version control and merging concepts, by discussing some.
Its not even really about patch theory, because im too lazy to read through the actual article on patch theory in enough detail. However, commutation always changes the context of a patch, and this may lead to changes in the effect of the patch. Key features include the ability to choose which changes to accept from other. Patch theory remains distinct in that it allows users to think of their repositories as unordered collections of changes. Feb 07, 2015 ps yes, the background theory in the readme provides a nice overview of the main ideas behind gitdeps, but i cant help but feel it contains an awkward mix of abstract descriptions the first and last paragraphs and concreteimplementationspecific information the two middle paragraphs. The theory is similar to that of darcs 2, so reading the paper on the camp site will also give an insight into how the current darcs patch theory works. When arjan records this change adding beer, we produce a patch which tells us not only what contents. That means that most of the time you are pushing and pulling changes you can cherrypick patches without a problem.
Camp is a project to develop and prove correct a darcslike patch theory, which will hopefully form the basis for darcs 3. But i have to admit that it still does not feel ready to go prime time. Feel free to edit it to add comments etc, but please dont change the core notation without discussing it on the mailing list first. In this article, i will try intro duces the basic ideas and operations of patch theory. The theory of patches is a theory of the many ways one can change the. Darcs patch theory is essentially about giving a precise definition to the ways in which patches and patch trees can be manipulated and transformed while maintaining the coherence of the repository. I should start by saying that i have obviously drawn a lot of ideas and inspiration from darcs, and especially from the wikibook explanation of darcs patch theory, but i do think there might be some nuggets of original contributions here in subsequent posts at least, but im not yet familiar enough with the literature. Feb 27, 2011 this is a nursing lecture about how to implement change is the system. A darcs patch can contain changes of the following kinds. It presents two challenges that i find troublesome. This default setting is valuable because the common case for longtime darcs users is to choose only a subset of edits to batch together into one darcs patch. An abstract theory of patches determines how changes from multiple.
Firstly, each copy of the source is a fully functional branch, and secondly, underlying darcs is a consistent and powerful theory of patches. Darcs is simple to learn and use, with a powerful new approach to meet the needs of todays distributed software projects. The representation of a patch defines what change that particular patch makes, and must be defined in the context of a specific tree. Why i dont use darcs any more much teideal glic deisbhealach. Homotopical patch theory carnegie mellon university. A theory of change describes how we believe that change could be made to happen and outlines the main elements for that change. This page contains discussion on properties of a darcslike patch system where the order of the patches within the repository does not affect its state. The replace command is useful for explicitly telling darcs to replace one word with another for example, a variable name, if you are a programmer note that because of the underlying patch theory, replace only works if the new word doesnt already exist in the file. Pijuls pristine is stored in a conflicttolerant data structure. How i stopped missing darcs and started loving git tom. Understanding darcspatch theory wikibooks, open books for. Pijul is mostly a formally correct version of darcs theory of patches, as well as a new algorithm for merging changes.
The current development strategy focuses on implementing optimizations and adding new features, while maintaining the same repository format. The developers also emphasize the use of advanced software tools for verifying. Below is an edited version of the theory of change developed. Darcs is, rather thrillingly, based on a theory of patches with roots in quantum mechanics, a notion which roundy brings down to earth a little in the interview. I somehow agree with the statement that it might hamper haskell projects since its performance is quite bad most of the time it took me 25 minutes to annotate a single file. Intuitively, a patch is a syntactic repre sentation of a function that changes a repository.
One of the great things about darcs is that we generally do not need rebase. Its not even really about patch theory, because im too lazy. Darcs is a distributed version control system with a flexible repos itory model. An assumption no matter how strongly you believe it to be true is, after all, an assumption. Darcs is a distributed version control system created by david roundy. The identity of a patch is invariant under patch commutation. Patch computing snapshot computer storage references.
In the toc, the primary challenges indicated are your underlying assumptions. Generally speaking, in darcs the order of patches is meaningless. I say may return because a patch starting at snapshot c might not exist. In darcs, there is no correct linear history of a repository rather, there is a poset of patches. However, for a team of developers, or even a single individual working across several machines, darcs isnt so great. It is implemented in the darcs engine as data structures for representing sequences of patches and haskell functions equivalent to the operations in. Darcs rebase is a new feature which may be available in darcs 2. This means, i think, that robins algorithm will do the right thing in cases where darcs merges correctly and git merges incorrectly git fails in these cases precisely because it doesnt track the source of each line by composing a sequence of. You can think of a darcs repository as containing these things.
This leads to both some architectural and implementation cleanup relative to darcs so that some confidence can be maintained between the formal proofs and the code. The discussion and the patch system presented here is based on davids patch theory, ganeshpatchalgebra and marnix kloosters patch calculus. Darcs patch theory is essentially about giving a precise definition to the ways in which patches and patchtrees can be manipulated and transformed while maintaining the coherence of the repository. Git should develop a hybrid approach a patch pool on top of a fixed branch line.
Lets return to the example from the beginning of this module. Know violence is now using the theory of change to help it secure funding and to guide the delivery, monitoring and evaluation of this important project. Understanding darcsprint version wikibooks, open books for. The biggest similarity is that these are both bag of patches models, unlike the gitmercurial dag of snapshots model. One of its distinguishing features is the theory of patches, that provides the theoretical foundations on which the tool is built. Understanding darcsprint version wikibooks, open books. I really like the idea of darcs and the patch theory and started to use it for home projects. At its most basic level, the theory of patches is about the commutation, or reordering, of changes in such a way that their meaning doesnt change. Also, some people just cant accept its mode of operation, and prefer something more explicit i dont blame them myself.
With darcs, such patches include addfile, rmfile, hunk remove andor add text lines to a file, adddir, rmdir, move change name of file or directory, replace and binary remove andor add binary content to a file. Ill define a theoretical function patch that takes an edit and a new starting state and returns the ending snapshot of a new edit. It is implemented in the darcs engine as data structures for representing sequences of patches and haskell functions equivalent to the operations in the formalism. A theory of change toc documents the change impact that you are seeking for both accountability and internal awareness of potential organizational challenges. So according to the this wikipedia page about merges in version control, darcs uses patch commutation and so does git when it rebases. Even git acquired a similar change selection feature at some point. The outcome is the same as darcs, the difference is that everything is explicit. The theory of patches is a theory of the many ways one can change the representation of a patch to place it in the context of a different tree. An abstract of the thesis of oregon state university. Jul 28, 2015 darcs is a patchcentric version control system. Darcs will helpfully let you know if you try to replace something you cannot. We do not describe exactly the theory that darcs 2 is built on, as it is known to have some problems, but our theory is similar to. In darcs, what if i want to reorder to the top or just throw away a patch which other patches depend on i.