A gentle introduction toClojure

(gentle (introduce Clojure)) - Talking with a LISPBy / Guy Taylor @xsyn

(def @xsyn)Ok, so who am I and why do I know anything?

I don't...

I've been playing with Clojure for about 3 years now - Makingme a Clojure blue belt.I'm a freelancer, currently building an analytics cluster forTYME, a mobile banking solutions provider.I'm the father of 5 month old twins (So I know a thing or two about concurrency).

(def introduction)“If you want everything to be familiar, you willnever learn anything new, because it can't besignificantly different from what you already

know and not drift away from the familiarity.”

Rich Hickey

Sure...but why Clojure?

Let's start by identifying what it is

(clojure.set/intersection Clojure Scala)Clojure and Scala are similiar in a number of ways

Functional languageHosted on the JVMJava interop

(clojure.set/difference Clojure Scala)Dynamically typedEnforced immutabilityIt's a LISP OMG! WTF? Brackets ?! Interrobang!

(def immutability)The hardest button to button...until..

The entire LISP universe is based around the following structure:

(def LISP)

(verb noun noun)

(so? Clojure)LISPs are awesomeReally cool toolingI've never had so much fun with a programming languageWorth the personal growth

(def scalar-literals)Characters

\c ; Character(class \c) ;= java.lang.Character\space\newline\formfeed\return\backspace\tab

Strings"hello" ; String(class "hello") ; = java.lang.String

;BUT strings are also collections. Which means that anything you can;do to a collection you can do to a string. Hold that thought...

(def scalar-literals)Numbers

42, 0xff, 2r111, 040 ; long (64 bit signed integer)3.14, 6.02139864 ; double (64 bit floating point decimal)42N ; clojure.lang.BigInt (arbitary precision integer)0.01M; java.math.BigDecimal (arbitary precision signed floating point decimal) 22/7; clojure.lang.Ratio

(def scalar-literals)Booleans

nil; niltrue; truefalse; false(= true 1); false(= false nil); false

Pretty straight foward, but they work in very different ways.

(def collection-literals)'(a b :name 2) ; list[a b :name 2] ; vector#{1 2 3} ; set{:name Guy :nick xsyn} ; map

Lists are not used as frequently as other Clojure collection types.

(def collection-literals)Lists

'(1 2 3) ; (1 2 3)(list 1 2 3) ; (1 2 3)(conj 4 (1 2 3) ; (4 1 2 3)(first '(1 2 3)) ; 1(second '(1 2 3)) ; 2(nth '(1 2 3) 2) ; 3;; Read in a linear order, NOT indexed, useful for small collections ;; Internally stored as a chain of values

Lists are not used as frequently as other Clojure collection types.

(def collection-literals)Vectors

[1 2 3] ; [1 2 3] (vec '(1 2 3)) ; [1 2 3](conj 4 (1 2 3) ; [1 2 3 4](next [1 2 3]) ; [2 3](= '(1 2 3) [1 2 3]) ; true;; Indexed, good for large collections, more frequently used than lists;; Internally stored as trees

(def collection-literals)Sets

#{1 2 3} ; #{1 2 3} (set [1 1 1 2 2 2 3 3 3]) ; #{1 2 3}(clojure.set/union #{1 2 3} #{4 5}) ; #{1 2 3 4 5}(clojure.set/difference #{1 2 3} #{2 3}) ; #{1}(clojure.set/intersection #{1 2 3} #{2 3}) ; #{2 3};; Unique items in set, mathematical sets

(def collection-literals)Maps

{:name "Guy" :nick "xsyn" :age 34} ; {:age 34, :name "Guy", :nick "xsyn"}(def xsyn {:name "Guy" :nick "xsyn" :age 34}) ; #'/xsyn(keys xsyn) ; (:age :name :nick)(vals xsyn) ; (34 "Guy" "xsyn")(get xsyn :name} ; ("Guy")(:name xsyn) ; ("Guy")(merge xsyn {:languages {:clojure true:scala false})); {:name "Guy" :nick "xsyn" :age 34 :languages {:clojure; true :scala false}(get-in {:name "Guy" :nick "xsyn" :age 34 :languages {:clojure true :scala false} [:nick :languages]}(get-in xsyn [:languages :scala]) ;nil(get-in {:name "Guy" :nick "xsyn" :age 34 :languages {:clojure true :scala true}} [:languages :clojure]) ; true ;; Do not retain sequence

(def PersistentVector)(def brown [0 1 2 3 4 5 6 7 8])(def blue (assoc brown 5 'beef))

Source: http://hypirion.com/musings/understanding-persistent-vector-pt-1

(defn f [x] (f x))Functions are the verbs of Clojure, everything you do you do

through f [x].

(defn count-to-infinity [number] "Print numbers to infinity. You should probably not run this" (println count-to-infinity (inc number)))

(defn fibs [] "Fibonnaci sequence demo function" (map first (iterate (fn [[a b]] [b (+ a b)]) [0 1])))

Functions turn values into values.

(defmacro f [x] (f x))Macros turn code into code.

(defmacro ignore "Cancels the evaluation of an expression, returning nil instead." [expr] nil)

user=> (ignore (+ 1 2))nil

(ns foo.bar)Mappings from symbols to vars and classes

(ns data.core (:use [incanter.core] [incanter.io] [incanter.charts] [data.helpers] [clj-time.format :as t]))

(defn datemap [date] "Date formatter" (parse (t/formatter "YY/MM/dd") date))

(.interop Java)(defn fetch-url[address] (with-open [stream (.openStream (java.net.URL. address))] (let [buf (java.io.BufferedReader. (java.io.InputStreamReader. stream))] (apply str (line-seq buf)))))

#'user/fetch-url

user=> (fetch-url "http://google.com")

"<!doctype html>...

...</html>"

;; Importing Java libraries(import '(java.io FileReader))

Leiningenfor automating Clojure projects without setting your hair

on fire

Building a project$ lein new foobar

Generating a project called foobar based on the 'default' template.To see other templates (app, lein plugin, etc), try lein help new.

$ cd foobar && ls

LICENSE README.md doc project.clj resources src test

Boilerplate Project.clj(defproject foobar "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"]])

Actual Project.clj(defproject data "0.1-alpha" :description "Data shunting playground" :license {:name "Eclipse Public License" :url "http://www.eclipse.org/legal/epl-v10.html"} :dependencies [[org.clojure/clojure "1.5.1"] [incanter/incanter-core "1.5.4"] [incanter/incanter-io "1.5.4"] [incanter/incanter-charts "1.5.4"] [incanter/incanter-excel "1.5.4"] [clj-time "0.6.0"] [org.clojure/data.json "0.2.1"] [org.apache.hadoop/hadoop-core "1.1.2"] [org.clojure/data.csv "0.1.2"]] :main data.core :jvm-opts ["-Xmx6G" "-server" "-Djsse.enableSNIExtension=false"] )

Source:

(def ungoogleable)A bunch of symbols that you'll see, but will find hard to

googleSome Examples:

# ; The Dispatch Macro#{ ; The set macro, we've already seen this#_ ; The discard macro#" ; The regular expression macro#( ; The function macro#' ; The var macro% ; Argument placeholder@ ; Deref macro ; Metadata

http://yobriefca.se/blog/2014/05/19/the-weird-and-wonderful-characters-of-clojure

(lazy-seq (doc introductions))Books

Clojure Programming - Chas Emerick

The Joy of Clojure - Michael Fogus

(lazy-seq (doc introductions))Videos

http://www.infoq.com/author/Rich-Hickey

Are we there yet - Rich HickeyThe value of values - Rich HickeySimple made easy - Rich Hickey

While these are videos are by Clojure's author, they shine lighton the philisophical underpinnings of Clojure, and are worth

watching even if you never touch it.

(lazy-seq (doc introductions))Online

Clojure-Koans: http://clojurekoans.comAphyr’s Clojure from the ground up:http://aphyr.com/posts/301-clojure-from-the-ground-up-welcomeIRC: freenode.irc.net - #Clojure #Clojure.zaBUILD SOMETHING

(questions? presentation)(thank you) (follow @xsyn)

Presentation available on Github at:https://github.com/xsyn/intro-to-clojure