ZeroMQ is a simple and robust asynchronous messaging layer.¹ Unfortunately, using it with Clojure is far from simple. The steps below are the magic key that worked for me:

• Starting out nice and slow, install the core zmq libraries and command line tools with homebrew:²

  brew install zmq
  

• With ZMQ installed, you're ready to start building jzmq, the Java bindings. You'll need to patch the homebrew formula for pkg-config, as jzmq requires the latest-and-greatest to build correctly³

  brew edit pkg-config
  

  require 'formula'
  
  class PkgConfig <Formula
    homepage 'http://pkgconfig.freedesktop.org'
    url 'http://pkgconfig.freedesktop.org/releases/pkg-config-0.25.tar.gz'
    md5 'a3270bab3f4b69b7dc6dbdacbcae9745'
  
    def install
      paths=%W[#{HOMEBREW_PREFIX}/lib/pkgconfig /usr/local/lib/pkgconfig /usr/lib/pkgconfig /usr/X11/lib/pkgconfig].uniq
      system "./configure", "--with-pc-path=#{paths*':'}", "--disable-debug", "--prefix=#{prefix}"
      system "make install"
    end
  end
  

• At this point, you'll need to copy one of the essential pkg-config files into a location that jzmq's build tools can find.⁴

  sudo cp /usr/local/Cellar/pkg-config/0.25/share/aclocal/pkg.m4 /usr/share/aclocal/pkg.m4
  

• Now we're ready to build jzmq. This will build the dylib you'll need to actually use the bindings, and places it in /usr/local/lib.⁵

  git clone git://github.com/zeromq/jzmq.git
  cd jzmq
  ./autogen.sh
  ./configure
  make
  sudo make install
  

• Getting closer! We'll need the zmq.jar file produced during the build, so copy that into your project's lib directory:⁶

  cp ./src/zmq.jar /path/to/my/project/lib/zmq.jar
  

• Now we can actually start setting up Clojure for ZMQ. Edit your leiningen project.clj file:

  (defproject my-project "1.0.0-SNAPSHOT"
    :description "FIXME: write"
    :dependencies [[org.clojure/clojure "1.2.0"]
                   [org.clojure/clojure-contrib "1.2.0"]
                   [org.clojars.mikejs/clojure-zmq "2.0.7-SNAPSHOT"]]
    :dev-dependencies [[swank-clojure "1.2.1"]]
    ; This sets the 'java.library.path' property
    ; so Java can find the ZeroMQ dylib
    :native-path "/usr/local/lib")
  

• Collect the leiningen dependencies:

  lein deps
  

• Start your swank server:

  lein swank
  

• Bask in the results with the canonical example:

  (ns my-project.core
    (:use [org.zeromq.clojure :as zmq]))
  
  (defn- string-to-bytes [s] (.getBytes s))
  (defn- bytes-to-string [b] (String. b))
  
  (defn test-zmq []
    (let [ctx (zmq/make-context 1)
  	socket (zmq/make-socket ctx zmq/+upstream+)]
      (zmq/connect socket "tcp://127.0.0.1:5555")
      (while true
        (println (bytes-to-string (zmq/recv socket))))))
  

This process is definitely rough around the edges, but I hope it helps you get started quickly!