This page compiles projects ideas for people (eg students) who are looking for medium-to-large projects to work on Darcs. These ideas can be also useful for a Google Summer of Code project.

HTTP system overhaul

Currently Darcs depends by default on the C library curl to handle file download by HTTP. Alternatively, it can depend on the Haskell library HTTP.

We would like to experiment switching to a newer system like wreq, or req (see motivation wrt wreq ).

This means making (w)req the default download system. We might keep the current libcurl and HTTP code for benchmarking purposes, but given its rather complex interface it may be simply better to replace it entirely and benchmark against darcs pre-replacement.

It might make sense to deliver this as an independent “download manager” library. This would encourage a clean design that’s not too coupled with darcs, and potentially be of benefit to the Haskell community as a whole.

The benefits would be:

Deliverables (apart from the code itself):

  • HTTP benchmarks ((w)req vs libcurl vs HTTP)
  • testing that pipelining actually works
  • testing under windows / linux

Darcs does not currently send any file by HTTP but if we enable HTTP push it would be nice to benchmark HTTP send anyway.


Darcsden is the repository hosting software that runs on

We have various targets to make Darcsden easier to install and use.

  • unauthenticated patch submission via darcs send and http:
    • can/should be unauthenticated or require an account on darcsden?
    • how should submitted bundles be presented to the repository owner?
    • how does darcs detect that it should send to darcsden instead of doing a regular send?
    • desired outcome: easier way to contribute to a darcs project without having to configure sendmail
  • http push (to darcsden):
    • specify how darcs could push to a dumb server (without remote darcs), for instance via ssh
    • pushing to a dumb server requires changes in the working of push. this requires local darcs to download more files and do the merging work locally.
    • it would be useful to measure the tranfer costs of pushing to dumb server vs. pushing to server with remote darcs vs. pushing to a repository inside of a locally mounted sshfs folder vs the dumb way (clone local, pull from remote patches from it, delete remote repo, clone merged repo to
  • enhancing easiness of retrieving source code from darcsden without having darcs:
    • automatic creation of git mirrors? (stretch goal)

See also the list of issues of Darcsden on

Conflicts handling/UI

Survey: How can we enhance conflict handling within the limits of the current Darcs repository format / specification ?

What about darcs-1 semantics?

See also page 10 of Ganesh’s talk


Improve fast-export with regard to conflicting patches. Because of how darcs handles conflicts, some information can be lost with the current way of creating incremenal mirrors to git (with convert export). An approach to address this would be to only resume exporting when the source repo is in a non-conflicting state (to at least have a history log that is faithful to the source repo). We could warn users about conflicts. Or maybe we can export all conflicting patches in some way, into the git mirror repository (branches?). See previous discussions on this topic:

Also fast-export is not faithful with respect to dirty tags.

We probably need some “calculate patch dependency graph” computation to export a darcs history as a branching one. Do we need to export branches as much as possible or only branch in presence of tags and conflicts?

Darcs as a conflict-resolution tool for any VCS

Resolving conflicts during a merge in any VCS involves (at least implicitly) reconstructing the semantic intent of the changes on each side, and then applying them on top of each other.

Darcs patches are a great way of expressing semantic intent explicitly. Build a tool based on darcs patches where the user can reconstruct the changes for both sides of the conflict as a chain of darcs patches, and then use the darcs merge result to actually resolve the conflict (or at least cut it down). As well as the existing darcs patch types, this offers a lot of scope for adding new types just for the tool, as we won’t need to worry about the usual backwards compatibility concerns - for example it might try to parse the changes as source code. The tool can also try to automatically infer the patches as well as allowing the user to enter them explicitly.

Distributed issue tracking for darcsden

Change the darcsden issue tracker to store the issues themselves in a separate darcs repository. Other people have tried distributed issue tracking before so this also involves investigating previous solutions.

Patch dependencies

  • show on whatsnew and record on which changes do the unrecorded changes sit
  • automatically discover patch dependencies (amend --ask-deps) when given test fails without them
  • visualization of patch dependencies

Survey: short, secure, fast version identifiers


Do a survey of what Darcs could use as short, secure, fast version indentifiers. Compare Darcs vs Git in this aspect. Estimate costs of implementing a system above the existing.

Memory profiling and optimizations


Benchmark memory consumption of Darcs and optimize its most memory hungry functions.

See in particular:

See also:

Bucketed repositories

Recently (in version 2.10), darcs’ global cache got bucketed, ie, hashed files were stored in subdirectories ./00/ , ./01/, ./02/ , etc. instead of a single big directory (thus dividing file # by 256 which concretely is more manageable by many filesystems).

What are the costs of doing the same at the repository level? What about existing repositories? What about current Darcs versions versus new bucketes repositories?

Can darcsden be made compatible with old darcs clients, by means of HTTP redirections?

Is it worth it?

Spin off libraries from Darcs

This is the perfect project for a non-darcs Haskeller to get on. Good for us, good for the whole Haskell community. Approach : identify likely haskellers (e.g. authors/maintainers of respective hackage packages) and ask for their help?

List of things that probably should be spun off into standard libraries (or merged with, replaced with, etc):

  • Diff detection, edit distance, lcs, code
  • Crypto stuff (issue2043)
  • Date parsing
  • System.Posix stuff for windows (package: unix-compat ?)
  • Fetching remote files (curl on Hackage, but maybe generic wrapper for curl/libwww/HTTP)
  • Advanced printing: Darcs.ColorPrinter and Printer (issue1598)
  • MIME parsing/generation

Darcs under windows

Review Darcs under windows, how can it be made easier to install and use?

Survey: darcs on a dumb server

How can we improve this use case? What’s the state of darcs on sshfs now?

Survey exception use in Darcs

Watch out for catch, catchall and such.

File similarity

Detecting file similarity and detect files moves and hunk moves. See

Darcs support for existing GUI

Add a darcs support to an existing GUI, for instance (Python) or (proposed in


We still don’t have a manual for Darcs >= 2.10. Want to help us?

In-browser javascript client

Obviously not an Haskell project. See JSClient.

Other projects

Keep in mind that you could always propose an project with a whole different set of ideas. Be creative! :-)