Clojure and Modularity

Clojure and Modularity Philly Lambda Tuesday, July 21, 2009 Stuart Sierra http://stuartsierra.com/

Clojure's Four Elements List (print :hello "Philly") Vector [:eat "Pie" 3.14159] Map {:lisp 1 "The Rest" 0} Set #{2 1 3 5 "Eureka"}

defn (defn greet [name] (println "Hello," name)) (defn average [& args] (/ (reduce + args) (count args)))

Data are Functions ({:f "foo" :b "bar"} :f) "foo" (:key {:key "value", :x "y"}) "value" ([:a :b :c] 2) :c (#{1 5 3} 3) true

defmacro (defmacro when [test & body] (list 'if test (cons 'do body)))

Java (import '(com.example.package MyClass YourClass)) (.method object argument) (MyClass/staticMethod argument) (MyClass. argument)

synchronous asynchronous coordinated ref independent atom agent unshared var

Vars (def life 42) (defn meaning [] (println life)) (meaning) 42 (binding [life 37] (let [life 37] (println life) (meaning)) (meaning)) 37 37 42

Refs (def c (ref 100)) (deref c) 100 (dosync (alter c inc)) (deref c) 101

Agents (def fib (agent [1 1 2])) (deref fib) [1 1 2] (send fib conj 3 5) returns immediately! later on... (deref fib) [1 1 2 3 5]

clojure.contrib.http.agent (http-agent "http://www.altlaw.org/" :on-success (fn [a] (println (response-body-str a))))

Multimethods (defmulti copy (fn [in out] [(class in) (class out)]))

Multimethods (defmethod copy [InputStream OutputStream] .. (defmethod copy [InputStream Writer] ... (defmethod copy [InputStream File] ... (defmethod copy [Reader OutputStream] ... (defmethod copy [Reader Writer] ... (defmethod copy [Reader File] ... (defmethod copy [File OutputStream] ... (defmethod copy [File Writer] ... (defmethod copy [File File] ...

Namespaces (ns my.cool.project (:require [clojure.contrib.math :as math]) (:import (java.math BigDecimal))) (defn lower-median [x y] (math/floor (/ x y))

Modularity and Dependency Management ● CPAN ● OSGi ● Python Eggs ● Maven ● Rubygems ● Ivy ● PEAR (PHP)

Modularity Your program Library X Library Y Library Z, Library Z, version 1 version 2

"JAR hell" Your program x.jar y.jar Library X Library Y Library Z, Library Z, version 1 version 2

CPAN ● System-wide or per-user library installation ● User manages libraries ● One repository, many mirrors ● Multiple versions of a lib may be installed; each process may only use one version ● Integrated docs, tests, & bug tracker

Rubygems ● System-wide or per-user library installation ● User manages libraries ● Multiple repositories, names may conflict ● Multiple versions of a lib may be installed; each process may only use one version ● Docs, tests, and bug tracking not integrated

ASDF ● System-wide or per-user library installation ● User manages libraries ● Wiki page acts as the repository! ● No integrated docs/tests/bug-tracking ● Does not support multiple versions of the same lib

Maven / Ivy ● Per-project library installation ● Build system manages libraries; user manages private repository ● Multiple public repositories ● Optional integration with docs/tests ● Permits multiple versions of a same lib, must be handled by a framework

OSGi ● Java EE, Glassfish, Eclipse ● Bundle: JAR file + extra manifest headers ● Each Bundle gets its own ClassLoader ● Multiple, nested ClassLoader contexts within a single JVM

More ● http://clojure.org/ ● Google Groups: Clojure ● #clojure on irc.freenode.net ● http://github.com/richhickey/clojure-contrib ● http://stuartsierra.com/ ● http://github.com/stuartsierra ● http://www.altlaw.org/

Clojure and Modularity

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