This chapter is all about Reactive Extensions, so let's go ahead and create a project called rx-playground that we will be using in our exploratory tour. We will use RxClojure (see https://github.com/ReactiveX/RxClojure), a library that provides Clojure bindings for RxJava() (see https://github.com/ReactiveX/RxJava):

$ lein new rx-playground

Open the project file and add a dependency on RxJava's Clojure bindings:

(defproject rx-playground "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
  :dependencies [[org.clojure/clojure "1.5.1"]
                 [io.reactivex/rxclojure "1.0.0"]])"]])

Now, fire up a REPL in the project's root directory so that we can start creating some observables:

$ lein repl

The first thing we need to do is import RxClojure, so let's get this out of the way by typing the following in the REPL:

(require...