Talk on Clojure infrastructure given at OSCON 2010.

1. Practical Clojure
Programming
Howard M. Lewis Ship
TWD Consulting
hlship@gmail.com
1 © 2010 Howard M. Lewis Ship

2. Agenda
• Build Tools
• Sharing Your Code
• IDE Support
2 © 2010 Howard M. Lewis Ship

3. Build Tools
3 © 2010 Howard M. Lewis Ship

4. Leiningen
“A build tool for
Clojure designed
to not set your
hair on fire”
4 © 2010 Howard M. Lewis Ship
“Leiningen Versus the Ants” is a short story from 1938 about a plantation owner fighting a battle against 20 square miles of Army Ants.
http://en.wikipedia.org/wiki/Leiningen_Versus_the_Ants

5. $ lein compile
lein
(shell script)
leiningen.jar
project.clj
(Clojure)
Maven Ant
Ant tasks Clojure
Tasks
Copying, AOT Dependency
packaging Compilation Resolution
5 © 2010 Howard M. Lewis Ship

6. 6 © 2010 Howard M. Lewis Ship
lein is a Unix shell script; self-install downloads Clojure and the Leiningen JARs from http://github.com/downloads/technomancy/
leiningen
I had previously added ~/bin to my Unix $PATH
Note: Most of this presentation was done with an alpha version of Leiningen 1.2 (I may need to update the movie to reflect this
properly)

7. common lein
commands
• new — create empty project
• deps — download dependencies to lib
• compile
• test
• jar
• clean
7 © 2010 Howard M. Lewis Ship

8. 8 © 2010 Howard M. Lewis Ship
lein uses some Maven infrastructure; downloaded dependencies live in ~/.m2/repository (the download is needed just once)

9. .
|-- README
|-- lib
| |-- clojure-1.1.0.jar
| `-- clojure-contrib-1.1.0.jar
|-- project.clj
|-- src
| `-- com
| `-- howardlewisship
| `-- example
| `-- core.clj
`-- test
`-- com
`-- howardlewisship
`-- example
`-- core_test.clj
9 © 2010 Howard M. Lewis Ship

10. project.clj
(defproject com.howardlewisship/example "1.0.0-SNAPSHOT"
:description "FIXME: write"
:dependencies [[org.clojure/clojure "1.1.0"]
[org.clojure/clojure-contrib "1.1.0"]])
10 © 2010 Howard M. Lewis Ship

11. Cascade
.
|-- lib
| `-- dev
|-- project.clj
|-- src
| |-- main
| | |-- clojure
| | `-- resources
| `-- test
| |-- clojure
| |-- resources
| `-- webapp
`-- target
`-- classes
11 © 2010 Howard M. Lewis Ship
http://hlship.github.com/cascade/

12. (defproject com.howardlewisship.cascade/cascade-core "1.0.0-SNAPSHOT"
:description "Simple, fast, easy web applications in idiomatic Clojure"
:url "http://github.com/hlship/cascade/"
:dependencies
[[org.clojure/clojure "1.1.0"]
[org.clojure/clojure-contrib "1.1.0"]
[org.slf4j/slf4j-api "1.5.2"]
[org.slf4j/slf4j-log4j12 "1.5.2"]
[log4j/log4j "1.2.14"]]
:dev-dependencies
[[org.eclipse.jetty/jetty-server "7.0.0.RC4"]
[org.eclipse.jetty/jetty-servlet "7.0.0.RC4"]
[org.easymock/easymock "2.5.1"]
[org.seleniumhq.selenium.server/selenium-server "1.0.3"
:classifier "standalone"]]
:aot [cascade.filter]
:warn-on-reflection true
:main cascade.version
:source-path "src/main/clojure"
:test-path "src/test/clojure"
:resources-path "src/main/resources"
:test-resources-path "src/test/resources"
:compile-path "target/classes"
:jar-dir "target")
12 © 2010 Howard M. Lewis Ship

13. Group Id Artifact Id Version
(defproject com.howardlewisship.cascade/cascade-core "1.0.0-SNAPSHOT"
:description "Simple, fast, easy web applications in idiomatic Clojure"
:url "http://github.com/hlship/cascade/"
13 © 2010 Howard M. Lewis Ship

14. :dependencies — Runtime Dependencies
:dev-dependencies — Build/Test Dependencies
Group Id
[org.clojure/clojure-contrib "1.1.0"]
Artifact Id Version
[org.seleniumhq.selenium.server/selenium-server
"1.0.3" :classifier "standalone"]
[log4j "1.2.15" :exclusions
[javax.mail/mail
javax.jms/jms]]
14 © 2010 Howard M. Lewis Ship
:dependencies will become transitive dependencies of other projects that depend on this one (unless excluded)
:dev-dependencies are just used for testing, or as a source of lein plugins

15. Maven Repositories
• central — http://repo1.maven.org/maven2
• clojure — http://build.clojure.org/releases
• clojure-snapshots — http://
build.clojure.org/snapshots
• clojars — http://clojars.org/repo/
15 © 2010 Howard M. Lewis Ship

16. :omit-default-repositories true
:repositories {
"jboss" "https://repository.jboss.org/nexus/
content/repositories/releases/"
}
Additional repositories: id and URL
16 © 2010 Howard M. Lewis Ship

17. Compile all source files
in :source-path directory
:aot — vector of namespaces to AOT compile, or :all
:namespaces — deprecated alternative to :aot
:warn-on-reflection — Compiler warning when Java
method invocation requires reflection
:main — Namespace containing a main function,
becomes Main-Class Manifest entry
17 © 2010 Howard M. Lewis Ship
Reflection is needed when invoking Java methods on objects without type hints (on the receiving object, and for the method
parameters). Clojure just knows its an object, but hasn't enough type information to determine at build time what the particular method
to invoke will be. This is a big performance hit.

18. cascade/version.clj
(ns ^{:doc "Main function to display the version number of the framework"}
cascade.version
(:use [cascade config])
(:gen-class)) Command line args
(defn -main [& args]
(println (format "Cascade version %s" (read-config :cascade-version))))
$ lein uberjar
...
Created target/cascade-core-1.0.0-SNAPSHOT-standalone.jar
~/clojure-workspace/cascade
$ java -jar target/cascade-core-1.0.0-SNAPSHOT-standalone.jar
Cascade version 1.0.0-SNAPSHOT
~/clojure-workspace/cascade
$
18 © 2010 Howard M. Lewis Ship
At time of writing, uberjar would not work except with the default :jar-dir of . (I slightly doctored the text to show what it will look like
once fixed).

19. :compile-path "target/classes"
:source-path "src/main/clojure"
:test-path "src/test/clojure"
:resources-path "src/main/resources"
:test-resources-path "src/test/resources"
:compile-path "target/classes"
:jar-dir "target"
Where to put
Where to create compiled namespaces
constructed JARs
:compile-path classes
:source-path src
:test-path test
:library-path lib
:resources-path resources
:test-resources-path test-resources
:jar-dir .
19 © 2010 Howard M. Lewis Ship

20. Lein Issues
• Horrible, confusing name
• Targets Maven more than Ant
• Only one command at a time
• Little bit slow to start
• Documentation is terrible
20 © 2010 Howard M. Lewis Ship

21. Maven
21 © 2010 Howard M. Lewis Ship
http://maven.apache.org
http://github.com/talios/clojure-maven-plugin

22. Cold clean compile:
4m 32s
12 MB (392 files)
Clean compile:
40s
22 © 2010 Howard M. Lewis Ship
pom.xml available at http://github.com/hlship/cascade/blob/maven-build/pom.xml

23. Maven Issues
• Confusing & distressing to use
• Huge, ugly XML build file
• Lots of weird downloads on first use
• Slower than Lein
• Wouldn't compile cascade.filter Why?
23 © 2010 Howard M. Lewis Ship

24. Gradle
24 © 2010 Howard M. Lewis Ship
http://gradle.org/
http://bitbucket.org/kotarak/clojuresque/

25. Cold clean compile:
3m 30s
27 MB (129 files)
Clean compile:
40s
25 © 2010 Howard M. Lewis Ship
build.gradle available at http://github.com/hlship/cascade/blob/gradle-build/build.gradle

26. Gradle Summary
• Very slick in many areas
• Need to learn some Groovy syntax
• Not as focused/succinct as Lein
• Clojuresque plugin very immature
• Better documentation, still occasionally
patchy
• No real docs for Clojuresque
26 © 2010 Howard M. Lewis Ship
CLI has many useful features such as clean quick way to display dependencies; it's also cleaner about reporting downloads from
remote repositories. It's a more fully featured build system, but it's also a lot to take in.

27. Build Summary
• Try Lein, hope for the best
• Keep tabs on Gradle & Clojuresque
• Avoid Maven
• AOT Compilation of libraries a problem
27 © 2010 Howard M. Lewis Ship
A irritation now is that AOT compilation (which can be necessary in many cases) can cause unwanted compilation of namespaces
from libraries. See http://www.assembla.com/spaces/clojure/tickets/322

28. Sharing Your Code
28 © 2010 Howard M. Lewis Ship

29. 29 © 2010 Howard M. Lewis Ship

30. 30 © 2010 Howard M. Lewis Ship

31. 31 © 2010 Howard M. Lewis Ship
Why not "lein push"? the necessary Lein plugin is compiled against Clojure 1.1 and Cascade is tracking against 1.2. Fall down, go
boom. This is usually a problem with code that requires AOT, which it the case for cascade.filter. Still, it's very unfortunate.
I use SSHKeyChain.app to help manage my SSH sessions; otherwise I'd be prompted for my secret key when I execute the scp
command.

32. 32 © 2010 Howard M. Lewis Ship

33. IDE Support
33 © 2010 Howard M. Lewis Ship

34. Eclipse
• Counterclockwise 0.0.95.RC2
• http://code.google.com/p/counterclockwise/
34 © 2010 Howard M. Lewis Ship

35. 35 © 2010 Howard M. Lewis Ship

36. IntelliJ IDEA
• La Clojure 0.2.267
• Built-in to community edition
36 © 2010 Howard M. Lewis Ship
La Clojure was one of the first IDE plugins available

37. 37 © 2010 Howard M. Lewis Ship

38. NetBeans
• NetBeans 6.9
• Enclojure 1.2.1
38 © 2010 Howard M. Lewis Ship
Installation details at http://www.assembla.com/wiki/show/clojure/Getting_Started_with_Netbeans_and_Enclojure

39. 39 © 2010 Howard M. Lewis Ship

40. Emacs
40 © 2010 Howard M. Lewis Ship

41. IDE Support
• Frustrating
• NetBeans feels most advanced
• AOT support limited in all
41 © 2010 Howard M. Lewis Ship

42. Wrap Up
• Explosive growth in Clojure interest
• Tools just catching up
• Like Java in 2001?
42 © 2010 Howard M. Lewis Ship

43. Slides
• Will be available on SlideShare
http://www.slideshare.net/hlship
• … and rate me at SpeakerRate:
http://speakerrate.com/speakers/3749-
howard-m-lewis-ship
43 © 2010 Howard M. Lewis Ship

44. © 2009 fdecomite
http://www.flickr.com/photos/fdecomite/3185386870/
© 2008 Hallvard E
http://www.flickr.com/photos/eldholm/2354982554/
© 2005 Steve Jurvetson
http://www.flickr.com/photos/jurvetson/70704300/
© 2006 Chris Walton
http://www.flickr.com/photos/philocrites/245011706/
© 2007 Howard Gees
http://www.flickr.com/photos/cyberslayer/952153409/
© 2007 pickinjim2006
http://www.flickr.com/photos/81838529@N00/525129498/
© 2005 Jean-Philippe Daigle
http://www.flickr.com/photos/jpdaigle/59942231/
© 2007 QQ Li
http://www.flickr.com/photos/ozyman/443545349/
© 2008 MadAboutCows
http://www.flickr.com/photos/madaboutcows/2933510443/
© 2008 Martin Junius
http://www.flickr.com/photos/m-j-s/2724756177/
44 © 2010 Howard M. Lewis Ship