# Trying out Pijul

Pijul is a version control system. So what? Everyone just uses git nowadays, right? Well, I personally already use git, Mercurial (because its model of pull/update makes more sense to me) and svn (because sometimes it’s just not worth it). So a fourth VCS is hardly a major marginal cost.

Besides, Pijul is interesting in a lot of ways. Git and Mercurial work very hard to pretend that patches are the basic unit, but in reality they store snapshots of files. In Pijul, patches really are fundamental; it is based on ‘patch theory’, pioneered by Darcs, another obscure VCS I’ve flirted with in the past. As one may expect from a Haskell project, patch theory is an application of category theory to a software engineering problem. This isn’t just abstract nonsense for the sake of fulfilling Haskeller stereotypes: patch theory is more intuitive (which is why other systems fake it in the UI), and makes both cherry-picking and merges easier.

Pijul has not (at the time of writing) had a 1.0 release yet, but it’s self-hosting; impressively so, with its own ‘Nest’ GitHub-alike that’s remarkably feature complete for such a young project. The documentation, like that of many similar hobbyist FOSS projects, is a little bit lacking—parts are out of date and it’s spread across a manual, README files and replies on the Discourse forum—but I’ve seen worse and a little reference to the source combined with educated guesswork seems to have been sufficient so far.

The main use I have in mind in particular for Pijul is to control my various dotfiles: configuration for i3, emacs, zsh, etc. At the moment they use vcsh which is horrendous overkill to the point where I never remember to commit or push anything. The other problem I have is maintaining parallel configuration across various different computers. For example, I want wifi and battery status indicators on my laptop, but not on my desktop. I haven’t found a satisfactory way to keep these parts of the configuration separate while syncing unrelated changes between the computers. I believe that it should be a lot smoother with patch theory. A new feature of the latest 0.11 release, partial clones, may well also be useful.

There are a lot of features missing: ignore files come immediately to mind, as running pijul status in my home directory shows a lot of junk I don’t want in the VCS. As far as I can tell, it’s also impossible to see the contents of a patch, or show diffs in pijul log output. And the docs are quite unclear on a lot of important questions. How do branches work? There are some discussions in the forums, but I can’t tell what’s ideas to be implemented, what’s newcomers asking questions and what’s how it actually works. I’ll post my issues into the forum, and I hope that I’ll be able to help transfer the answers into the official docs.