The design of Clojure

Transcript

1. The Design of Clojure Shantanu Kumar, Concur 1

2. Who am I? • Engineer @ Concur • Author of

   “Clojure High Performance Programming” • Open Source enthusiast: https://github.com/ kumarshantanu • @kumarshantanu on Twitter 2

3. Clojure • Created by Rich Hickey, 2007 • Eclipse Public

   License (OSS) • Website — https://clojure.org/ • Lisp • Functional • Hosted on JVM (and CLR, JS) 3

4. Big ideas • Pervasive immutability (Epochal time model) • First-class

   values • First-class functions • Performance • Host interoperability • First-class state management 4

5. –Stuart Halloway “Clojure feels like a general-purpose language beamed back

   from the near future.” 5

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

7. Interactive REPL 7

8. 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

9. Data structures • List: ‘(“Harry” 34 :male) — sequential access

   • Map: {:name “Harry” :age 34} • Set: #{:red :blue} • Vector: [“Harry” 34 :male] 9

10. Working with data structures 10

11. Functions 11

12. Code is data 12

13. 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

14. Working with collections 14

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

16. –Alan J Perlis “A language that doesn't affect the way

    you think about programming, is not worth knowing.” 16

17. Records 17

18. Records • Class semantics (memory layout) • Behave as maps

    • Immutable in the same way as maps 18

19. Protocols 19

20. Protocols • Behaviour contract • Polymorphism • Dispatch on target

    object type • Used as implementation details 20

21. No structural inheritance! But, there are value hierarchies Image source:

    https://xspblog.files.wordpress.com/2008/06/owl_yarly.jpg 21

22. Macros 22

23. Sample output 23

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

    24

25. Java interop 25

26. 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

27. Concurrency and state • Atoms — uncoordinated compare and swap

    • Agents — asynchronous sequential operations • Refs — Software Transactional Memory • Dynamic vars — Thread-local access 27

28. Thank you! @kumarshantanu 28