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Introduction to Clojure

Baishampayan Ghose
Baishampayan Ghose

This document is a presentation on functional programming using Clojure on the JVM. The presentation covers an introduction to Clojure including what it is, why it was created, and how it is better than other languages. It then discusses Clojure fundamentals like being a Lisp, being dynamic and functional. The remainder of the presentation covers Clojure syntax, basics like Hello World, sequences, Java interoperability, concurrency, multimethods, tools and resources for Clojure.

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Functional Programming on the JVM using Clojure Baishampayan Ghose In鍖nitely 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
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 4 / 31
What, why and how of Clojure What is Clojure? Why a new programming language? How is Clojure any better than X? 5 / 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 6 / 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
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 10 / 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
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 12 / 31
Hello, Clojure! hello.clj (ns hello) (defn hello "Say hello to name" [name] (str "Hello, " name "!")) (hello "Clojure") ; -> "Hello, Clojure!" 13 / 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 14 / 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 鍖rst item (rest s) Return a seq of the rest of elements 15 / 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 16 / 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
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 18 / 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
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 20 / 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
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 22 / 31
There is more! Metadata Destructuring Transients Zippers Futures, Promises clojure.contrib Ping me after the talk for details 23 / 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 24 / 31
Tools Emacs + SLIME + paredit ViMClojure Enclojure + IntelliJ IDEA Counterclockwise + Eclipse Leiningen 25 / 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 26 / 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
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 28 / 31
Questions? 29 / 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 30 / 31
Contacting me http://freegeek.in/ bg@infinitelybeta.com @ghoseb on Twitter 際際滷s on - http://bit.ly/gnunify-clojure In鍖nitely Beta is recruiting smart hackers! http://infinitelybeta.com/jobs/ CC BY SA 31 / 31

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Introduction to Clojure

  • 1. Functional Programming on the JVM using Clojure Baishampayan Ghose In鍖nitely Beta Technologies GNUnify 2010 1 / 31
  • 2. 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
  • 3. 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
  • 4. 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 4 / 31
  • 5. What, why and how of Clojure What is Clojure? Why a new programming language? How is Clojure any better than X? 5 / 31
  • 6. 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 6 / 31
  • 7. 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
  • 8. 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
  • 9. 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
  • 10. 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 10 / 31
  • 11. 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
  • 12. 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
  • 13. 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 12 / 31
  • 14. Hello, Clojure! hello.clj (ns hello) (defn hello "Say hello to name" [name] (str "Hello, " name "!")) (hello "Clojure") ; -> "Hello, Clojure!" 13 / 31
  • 15. 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 14 / 31
  • 16. 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 鍖rst item (rest s) Return a seq of the rest of elements 15 / 31
  • 17. 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 16 / 31
  • 18. 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
  • 19. 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 18 / 31
  • 20. Concurrency Simultaneous execution Avoid reading,yielding inconsistent data 19 / 31
  • 21. 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
  • 22. 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 20 / 31
  • 23. Multimethods Generalised indirect dispatch Dispatch on a arbitrary function of the arguments 21 / 31
  • 24. 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
  • 25. 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
  • 26. 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 22 / 31
  • 27. There is more! Metadata Destructuring Transients Zippers Futures, Promises clojure.contrib Ping me after the talk for details 23 / 31
  • 28. 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 24 / 31
  • 29. Tools Emacs + SLIME + paredit ViMClojure Enclojure + IntelliJ IDEA Counterclockwise + Eclipse Leiningen 25 / 31
  • 30. 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 26 / 31
  • 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
  • 32. 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 28 / 31
  • 33. Questions? 29 / 31
  • 34. 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 30 / 31
  • 35. Contacting me http://freegeek.in/ bg@infinitelybeta.com @ghoseb on Twitter 際際滷s on - http://bit.ly/gnunify-clojure In鍖nitely Beta is recruiting smart hackers! http://infinitelybeta.com/jobs/ CC BY SA 31 / 31