Practical Clojure Programming

Practical Clojure
Programming

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

Agenda

• Build Tools
• Sharing Your Code
• IDE Support


Build Tools


Leiningen

“A build tool for
Clojure designed
to not set your
hair on ﬁre”


“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

$ lein compile

lein
(shell script)

leiningen.jar
project.clj
(Clojure)

Maven Ant
Ant tasks Clojure
Tasks

Copying, AOT Dependency
packaging Compilation Resolution


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)

common lein
commands
• new — create empty project
• deps — download dependencies to lib
• compile
• test
• jar
• clean


lein uses some Maven infrastructure; downloaded dependencies live in ~/.m2/repository (the download is needed just once)

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"]])


(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")


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/"


: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]]


: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

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/


:omit-default-repositories true
:repositories {
"jboss" "https://repository.jboss.org/nexus/
content/repositories/releases/"
}

Additional repositories: id and URL


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


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.

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
$


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).

:source-path "src/main/clojure"
:test-path "src/test/clojure"
:resources-path "src/main/resources"
:test-resources-path "src/test/resources"
: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 .


Lein Issues

• Horrible, confusing name
• Targets Maven more than Ant
• Only one command at a time
• Little bit slow to start
• Documentation is terrible


Maven


http://maven.apache.org

http://github.com/talios/clojure-maven-plugin

Cold clean compile:
4m 32s
12 MB (392 ﬁles)

Clean compile:
40s


pom.xml available at http://github.com/hlship/cascade/blob/maven-build/pom.xml

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?


Gradle

http://gradle.org/

http://bitbucket.org/kotarak/clojuresque/

Cold clean compile:
3m 30s
27 MB (129 ﬁles)

Clean compile:
40s


build.gradle available at http://github.com/hlship/cascade/blob/gradle-build/build.gradle

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

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.

Build Summary

• Try Lein, hope for the best
• Keep tabs on Gradle & Clojuresque
• Avoid Maven
• AOT Compilation of libraries a problem


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

Sharing Your Code



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.

IDE Support

Eclipse

• Counterclockwise 0.0.95.RC2
• http://code.google.com/p/counterclockwise/


IntelliJ IDEA

• La Clojure 0.2.267
• Built-in to community edition

La Clojure was one of the ﬁrst IDE plugins available

NetBeans

• NetBeans 6.9
• Enclojure 1.2.1


Installation details at http://www.assembla.com/wiki/show/clojure/Getting_Started_with_Netbeans_and_Enclojure

Emacs


IDE Support

• Frustrating
• NetBeans feels most advanced
• AOT support limited in all


Wrap Up

• Explosive growth in Clojure interest
• Tools just catching up
• Like Java in 2001?


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


© 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/


Practical Clojure Programming

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