7 minute read

CIDER 0.7 is finally out and it’s an epic release! It’s without a doubt the most important release since the inception of the project about two years ago and it’s the biggest one in terms of features and code changes.

The release is special for a number of reasons. Allow me to quickly enumerate though them.


One of the huge problems we’ve had so far was that a lot of functionality that was present in SLIME + swank-clojure was missing in CIDER. For many people the transition between the two didn’t really feel like an upgrade (although it was advertised as such) - after all they lost things like inspection, tracing, apropos, caller cross-reference, the debugger, etc.

The reason this happened was CIDER’s initial approach of implementing features by inlining Clojure code within the Emacs Lisp code and evaluating this code in a dedicated nREPL session (called the tooling session), to avoid contaminating the results in the “primary” eval session. This approach had one upside (you didn’t need any extra deps (middleware) to run CIDER) and one huge downside (it’s impossible to maintain non-trivial inlined code; not to mention it’s not very practical). This meant that pretty much all third party libs were out of the equation and pretty much every advanced feature.

This problem was initially addressed by ritz, which provided some extra functionality built on top of extra nREPL middleware. As it was a separate project it was hard to be kept in sync with the flurry of changes in CIDER and was abandoned at some point. While ritz failed it had the right approach and it served as the principle inspiration for CIDER 0.7.

In CIDER 0.6 we introduced optional nREPL middleware for some operations (like completion, error reporting, var info) and in 0.7 the middleware stack was greatly extended, improved and promoted to a mandatory CIDER component. This has one downside (you’ll have to install it to leverage all of CIDER’s power) and a several upsides:

  • A lot of the heavy lifting is now done in pure Clojure code (see cider-nrepl) and it’s much easier to implement complex features now (not to mention - this code is much easier to maintain). This also means that it’s much easier for Clojure programmers to contribute to CIDER as a lot of functionality is just lots of Clojure code and very little Emacs Lisp code. I’m reasonably sure I’m one of the very few CIDER users who knows more Emacs Lisp than Clojure, so I consider this a big win.

  • It’s now easy to provide pretty similar level of support for both Clojure and ClojureScript as we can reconcile the differences between them in our middleware.

  • It’s easier to keep the code backwards compatible (which is a nightmare for inlined code).

  • There are no implicit dependencies in the system (unlike before).

Consider auto-completion - this feature was implemented in terms of evaluating some clojure-complete code with the assumption that clojure-complete is available in the environment you were using as CIDER assumed you had started the nREPL server using lein repl. This would fire up a REPL-y REPL and clojure-complete is a REPL-y dependency. Not everyone uses lein repl, though and REPL-y can always switch to another completion library in the future.

If you connected CIDER to an embedded nREPL server, you’d be greeted by a missing class error, as most apps don’t normally depend on clojure-complete. You’d be puzzled for a while, but eventually you’ll realize what the problem is.

Now we’re free to explicitly specify our deps and pick the best libraries for the job (as opposed to those that are available) - you’ll quickly notice how smarter auto-completion is now on Clojure, because we’re internally using the newer, faster and more feature-rich compliment library (note that we’re using a different library for ClojureScript completion).

  • Other projects can leverage some of our middleware - somewhat amusingly for Emacs users, vim-fireplace is using cider-nrepl as well.

At this point we’ve removed pretty much all inlined code (except some pretty-printing code) and that has yielded much improved eldoc, macroexpansion, documentation viewing (cider-doc will now display Javadoc in Emacs!!!), source browsing, etc.

We’ve also started bringing back some features we loved in SLIME, but were missing so far - the inspector, apropos and tracing are back. We’re now working on bringing back function call cross-referencing and debugging as well.

Note that CIDER will still work if you connect to an nREPL server that’s not using CIDER’s middleware. In this case you’ll get a warning and a pretty limited feature-set - source file loading, code evaluation, pretty-printing and error highlighting.


clojure-test-mode (which was more or less abandoned in terms of maintenance) finally has a successor in CIDER itself. cider-test provides more or less the same functionality, but is implemented in terms of nREPL middleware and is a more robust solution. As it’s part of CIDER it cannot ever be out-of-sync with CIDER as clojure-test-mode has often been lately.

cider-test is a little rough around the edges, but I’m fairly sure it has bright future ahead. Use it, love it, hate it and send us your feedback! We’d love to hear it.

P.S. We might extend this with support for other frameworks like midje and expectations, although that’s not high on our priority list.

Grimoire support

In addition to built-in Clojure & Javadoc you can now peruse the extended documentation provided by Grimoire from the comfort of your beloved editor. No more browser interruptions just to get a few usage examples of some function! C-c C-d g for the win!

Adding some extended Grimoire integration is definitely on the roadmap.

Increased bus factor

One of the biggest problems of the project so far was that fairly few people were involved with it. At one point it was mostly Tim, Hugo and me. At another it was mostly me. The bus factor was dangerously close to 1, which always worried me. Recently, however, a lot of people have been helping quite actively, which makes me more optimistic about the future. As much as I love CIDER I don’t want it to depend on one extremely busy and very clumsy person (each time I go hiking there’s a serious chance I’ll fall of a cliff or something).

I’d like to thank everyone for your wonderful contributions and single out a bunch of people for some outstanding work done by them:

  • Gary Trakhman is the one responsible for the good ClojureScript support we now boast. Fantastic work, Gary! You have a big thanks from me!
  • Jeff Valk did some mighty fine work on the var info retrieval, source navigation, documentation display and single-handedly implemented cider-test and cider-apropos. We all owe Jeff a huge thanks!
  • Hugo Duncan who constantly contributed patches, bug reports and ideas. His nrepl-ritz project provided a lot of inspiration for some of the existing middleware.
  • Ian Eslick contributed the new inspector.
  • Alexander Yakushev made so many improvements to his awesome compliment library for the needs of CIDER. Did you notice that you now get completion suggestions for locals? How amazing is that!
  • Dmitry Gutov implemented native support in CIDER for company-mode.

The Road Before Us

Obviously our work is far from over - we’re still lacking some crucial features (most notably a debugger) and a lot of code needs polish. This will obviously take some time and a lot of work to get right, but I’m confident we’ll get there.

I’d also want us to work a bit in the area of documentation - a manual, a cheatsheet, etc. Have a look at the issue tracker if you’d like to help out - we definitely need all the help we can get.

The 0.7 release required a massive amount of work and we spent more that 3 months to get it to a shippable state. With the bulk of the work behind us I hope we’ll be able to deliver new releases more frequently - on a monthly (or bi-monthly) basis.

I’d love to be able to raise a lot of money via crowd-funding and work on CIDER for an year or get hired by some company to work full-time on it, but that’s not going to happen. For one reason or another people rarely get excited about dev tools, so all of us have to work together to make CIDER the ultimate Clojure(Script) development environment.

If I knew how much work I’d have to do when I assumed the maintenance of CIDER exactly one year ago I might not have done it. Maintaining a project that’s pivotal to an entire community (I recall some article mentioning about half the Clojure devs were using it) is both a lot of work and a lot of stress and pressure. That said, it’s probably my favourite OSS project and I enjoy working on it immensely.

For all the gory details regarding new features and changes in CIDER 0.7 - take a look at the changelog.

That’s all from me, folks! Use CIDER, drink cider and prosper!