clojure-dependencies.md

Clojure Modules HOWTO

Referencing a module from a project

1. Create new project

   lein new app [appname]
   

2. (optional) Search for a module you want to add to your project

   lein search [modulename]
   

3. Reference the module in project.clj under the :dependencies by its identifier which is given in the form of [group-id/artifact-id version-string]. In the following example we add the [org.clojure/data.json "0.2.5"] dependency.

   :dependencies [[org.clojure/clojure "1.6.0"]
                  [org.clojure/data.json "0.2.5"]]

4. (optional) You can make lein explicitly download the dependencies by

   lein deps
   

Next time you do a lein repl or M-x cider-jack-in lein will download [org.clojure/data.json "0.2.5"] and start the java REPL with [org.clojure/data.json "0.2.5"] loaded.

###Usage from REPL

When you start lein REPL from the project directory lein will then look for the :dependencies key in project.clj, sees [org.clojure/data.json "0.2.5"] and appends the path for the [org.clojure/data.json "0.2.5"] library to the classpath when starting the java process for the REPL.

1. Start the REPL

lein repl

or in emacs: M-x cider-jack-in

2. Load the namespace of the dependency in lein repl by referencing the namespace of the library. here the the namespace for [org.clojure/data.json "0.2.5"] is clojure.data.json.

   (require '[clojure.data.json])

   Now it is possible to use functions from clojure.data.json:

   (clojure.data.json/read-str "{\"a\": [1,2,3]}")
   => {"a" [1 2 3]}

   Alternatively you can alias the namespace

   (require '[clojure.data.json :as json])

   Usage:

   (json/read-str "{\"a\": [1,2,3]}")
   => {"a" [1 2 3]}

Usage from .clj files

1. At the top of the clj file, you have a namespace specification like (ns myproj.core) add to this namespace the :require key to reference a namespace.

   (ns myproj.core
       (:require [clojure.data.json]))

Alternatively you can use a shorter name.

```clojure
(ns myproj.core
    (:require [clojure.data.json :as json]))
```

Additional reading

• http://blog.8thlight.com/colin-jones/2010/12/05/clojure-libs-and-namespaces-require-use-import-and-ns.html
• http://www.unexpected-vortices.com/clojure/brief-beginners-guide/libs-management-and-use.html
• http://blog.8thlight.com/colin-jones/2010/11/26/a-leiningen-tutorial.html
• http://stackoverflow.com/questions/9810841/clojure-loading-dependencies-at-the-repl
• http://stackoverflow.com/questions/7658981/how-to-reload-a-clojure-file-in-repl
• https://github.com/technomancy/leiningen/blob/stable/doc/TUTORIAL.md