The Clojure Ecosystem

The Clommunity

Recently starting programming in Clojure, the somewhat lackluster state of some of the Clojure community projects is striking. Programming languages thrive when there is an active community and Clojure seems a mixed bag. Clojure sees regular (non breaking) releases and some of Clojure books are amongst the best development books ever written.


Probably one of the tools that makes us sing songs of hope for Clojure is Leiningen. It’s an active project and it’s the defacto standard for building Clojure projects. It hasn’t crapped out on me once, I installed a few plugins with no issues and

IDE support

  • Sublime Text 2. The SublimeREPL project is pretty awesome, but it’s not Clojure specific. The REPL does start and being able to send snippets of code to the REPL is pretty neat. I’ve developed a few functions using this approach. The main issue is that the Repl is not using the Lein project but just starts a vanilla Repl. The Repl froze a few times: annoying. So I’d say it’s nice but not awesome.
  • Eclipse. Though both Eclipse and Intellij feel too heavy for a dynamic language, they do have plugins you can use. Counterclockwise is the Clojure plugin for Eclipse. It has support for Leiningen, but lacks support for running tests. Running a Repl  inside Eclipse feels odd but sending code snippets seems to work. I couldn’t figure out how to load the full project into the Repl, which is strange because Eclipse is so project oriented.
  • IntelliJ. La Clojure is the plugin for IntelliJ, maintained by Jetbrains (which ought to be a plus). Haven’t used it yet.
  • Emacs. There are several deceised Emacs clojure plugins, but one has emerged (survived): nrepl.el. I didn’t know Emacs, so trying it out was a bit of a struggle. Emacs uses Lisp for some parts, so I imagine it has good support for Clojure’s syntax. The commands available from nrepl make it seem like a very powerful option.


For SQL databases there is Korma, which still a bit minimal but it allowed me to do a fairly complex join query using aliases. It’s under active development, although I would advise to double check its working before using it in a live environment. Clojureql seems to be a more stable but also a bit stale alternative.


Solr is a popular Lucene based database, it has search features beyond regular SQL databases and it is generally well supported. I say generally because Solr seems to be a weak spot for Clojure. The main reason for this blog was the state of Clojure Solr libraries.

There are 4 Solr Clojure projects (that I could find).

  • clojure-solr seems to be the grand daddy given its age and the fact that one of the other projects is based on it. It’s dormant, even the forks are not up to date. 
  • solrclient is not really a project, more a one off trying to use Solr through its JSON interface.
  • solrclj is less dead and looks like a proper project. It hasn’t been updated to the latest Solr and Clojure versions though. If I’d fork one project to bring it up to date it would be this one.
  • star is, well, the rising star amongst these libraries. Only created hours ago and literally minutes after I started searching for Solr + Clojure on github. The big ‘cool’ here is that the author also created the famous Solr Ruby client rsolr. Though no real lines of Clojure have been written yet, from the first commit it already looks promising and this guy obviously knows what is required in a Solr client library.
  • icarus is a little bit more recent, there is a version that supports Solr 3.5 (4.2 is the most recent). It’s only for querying and looks like it’s no longer maintained. It’s based on clojure-solr.

Unit Testing


Clojure comes with a unit testing API build right into the core. It’s cool that you can start writing unit tests out the gate. Leiningen runs it out the box and for a Java developer with JUnit experience (like me), it just works.


I’ve been reading Brian Marik’s book on Clojure, he authored his own testing framework Midje. Haven’t looked at it yet, but worth a mention.


Lazytest was written by the same guy who did the default Clojure.test library. Lazytest has one main issue: it’s dead. The current development branch is unstable but also two years old, a fatal combination. It’s one giant rough edge and doesn’t seem to support Leiningen properly.


One nice feature of SBT (Scala’s Leiningen) is the automatic compilation and running of tests on source change. There are some attempts to add this to Lein, but projects are either undocumented, too old or test framework specific. I do hope I’ll find a lein plugin that just does ‘detect source change = rerun tests’


One library worth mentioning is Cheshire. I’ve only used one function (parse-string) so far but it’s a feature rich and fun library to use. Of course its main strength comes from Clojure itself because any JSON structure can be parsed to and from a Clojure data structure (of maps and vectors). Keys turning into keywords makes it a pleasure to work with JSON. The author Lee Hinman seems a very productive member of the Clojure community, check out his other projects.

For further exploration of Clojure, here’s a list of libraries and Leiningen plugins

The Clojure Ecosystem