Introduction to Clojure

Functional Programming on the JVM using Clojure Baishampayan Ghose Inﬁnitely Beta Technologies GNUnify 2010 1 / 31

Outline 1 Who am I? 2 What, why and how of Clojure 3 Fundamentals 4 Syntax 5 Hello, Clojure! 6 Sequences 7 Java Inter-op 8 Concurrency 9 Multimethods 10 There is more! 11 Tools 12 Resources 13 Q&A 14 Contacting me 2 / 31

Who am I? My name is BG and I am a Computer guy FP head Scale nerd Prog-lang lawyer Web standards ninja FOSS geek Startup-ist 3 / 31

What, why and how of Clojure What is Clojure? Why a new programming language? How is Clojure any better than X? 5 / 31

Fundamentals Clojure is a Lisp Clojure is dynamic Clojure is hosted on the JVM Clojure is functional Clojure is geared towards concurrency Free & Open Source 7 / 31

Integers — 1234567891234 Doubles — 3.14, BigDecimals — 1.23M Ratios — 22/4 Strings — “foo”, Characters — a b c Symbols — foo bar, Keyword — :foo :bar Booleans — true false, Null — nil Regex patterns — #“[a-zA-Z0-9]” 8 / 31

Data Structures Lists (1 2 3 4 5), (foo bar baz), (list 1 2 3) Vectors [1 2 3 4 5], [foo bar baz], (vector 1 2 3) Maps {:a 1 :b 2 :c 3}, (hash-map :x 1 :y 2) Sets #{foo bar baz} 9 / 31

Syntax There is no other syntax! Data structures are the code No other text based syntax, just different interpretations There is a fancy name for this — Homoiconicity 11 / 31

Syntax There is no other syntax! Data structures are the code No other text based syntax, just different interpretations There is a fancy name for this — Homoiconicity Everything is an expression All data literals stand for themselves, except — Symbols Lists 11 / 31

Hello, Clojure! hello.clj (ns hello) (defn hello "Say hello to name" [name] (str "Hello, " name "!")) (hello "Clojure") ; -> "Hello, Clojure!" 13 / 31

Sequences An abstraction over traditional Lisp lists Provides an uniform way of walking through data structures (seq coll) If collection is non-empty, return a sequence object (first s) Return the ﬁrst item (rest s) Return a seq of the rest of elements 15 / 31

Java Inter-op Wrapper free interface to Java Syntactic sugar to make Java invocation easy Core Clojure abstractions are Java interfaces Clojure functions implement Callable & Runnable Clojure sequence library works on Java iterables Easy to implement, extend Java interfaces (if needed) Almost identical to Java in terms of speed 17 / 31

Concurrency Simultaneous execution Avoid reading,yielding inconsistent data 19 / 31

Concurrency Simultaneous execution Avoid reading,yielding inconsistent data Synchronous Asynchronous Coordinated ref Independent atom agent Unshared var Table: Building blocks of Clojure concurrency 19 / 31

Multimethods Generalised indirect dispatch Dispatch on a arbitrary function of the arguments 21 / 31

Multimethods Generalised indirect dispatch Dispatch on a arbitrary function of the arguments Call sequence Call dispatch function on args to get dispatch value Find method associated with dispatch value 21 / 31

Multimethods Generalised indirect dispatch Dispatch on a arbitrary function of the arguments Call sequence Call dispatch function on args to get dispatch value Find method associated with dispatch value Else call default method, else error 21 / 31

There is more! Metadata Destructuring Transients Zippers Futures, Promises clojure.contrib Ping me after the talk for details 23 / 31

Tools Emacs + SLIME + paredit ViMClojure Enclojure + IntelliJ IDEA Counterclockwise + Eclipse Leiningen 25 / 31

Resources Programming Clojure by Stuart Halloway http://en.wikibooks.org/wiki/Clojure http://clojure.org http://groups.google.com/group/clojure http://planet.clojure.in http://clojure.blip.tv 27 / 31

Questions? 29 / 31

Contacting me http://freegeek.in/ bg@infinitelybeta.com @ghoseb on Twitter Slides on - http://bit.ly/gnunify-clojure Inﬁnitely Beta is recruiting smart hackers! http://infinitelybeta.com/jobs/ CC BY SA 31 / 31

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Introduction to Clojure

by Baishampayan Ghose

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