The design of Clojure - Speaker Deck

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The Design of Clojure Shantanu Kumar, Concur 1

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Who am I? • Engineer @ Concur • Author of “Clojure High Performance Programming” • Open Source enthusiast: https://github.com/ kumarshantanu • @kumarshantanu on Twitter 2

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Clojure • Created by Rich Hickey, 2007 • Eclipse Public License (OSS) • Website — https://clojure.org/ • Lisp • Functional • Hosted on JVM (and CLR, JS) 3

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Big ideas • Pervasive immutability (Epochal time model) • First-class values • First-class functions • Performance • Host interoperability • First-class state management 4

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–Stuart Halloway “Clojure feels like a general-purpose language beamed back from the near future.” 5

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Getting started with Clojure http://leiningen.org/ https://learnxinyminutes.com/docs/clojure/ http://www.braveclojure.com/ https://www.4clojure.com/ 6

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Interactive REPL 7

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Data types • Number: 42, -5.67, 22/7 • Boolean: true, false • Character: \x, \y, \newline, \space • String: “foo”, “bar” (multi-line literals are supported) • Symbol: ‘do-something, ‘bizfn • Keyword: :red, :blue • Nothing: nil 8

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Data structures • List: ‘(“Harry” 34 :male) — sequential access • Map: {:name “Harry” :age 34} • Set: #{:red :blue} • Vector: [“Harry” 34 :male] 9

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Working with data structures 10

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Functions 11

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Code is data 12

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Persistent Data-structures • Immutable (updates return new instances) • Structure sharing (Hash array mapped trie) • 32-way branching for O(<7) performance • Sustained performance across updates • Reference: “Ideal Hash Trees” (Phil Bagwell) 13

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Working with collections 14

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I want a loop! No automatic tail-call optimization 15

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–Alan J Perlis “A language that doesn't affect the way you think about programming, is not worth knowing.” 16

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Records 17

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Records • Class semantics (memory layout) • Behave as maps • Immutable in the same way as maps 18

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Protocols 19

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Protocols • Behaviour contract • Polymorphism • Dispatch on target object type • Used as implementation details 20

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No structural inheritance! But, there are value hierarchies Image source: https://xspblog.ﬁles.wordpress.com/2008/06/owl_yarly.jpg 21

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Macros 22

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Sample output 23

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Macros • Compile-time code manipulation • Because code is data 24

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Java interop 25

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Concurrent execution • CPU-bound and I/O-bound thread pools • `future`: Asynchronous one-time access • `pmap`: Concurrent CPU-bound processing • `promise/deliver`: Single producer-consumer • Java’s concurrent collections considered idiomatic 26

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Concurrency and state • Atoms — uncoordinated compare and swap • Agents — asynchronous sequential operations • Refs — Software Transactional Memory • Dynamic vars — Thread-local access 27

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Thank you! @kumarshantanu 28