stefan kanev: clojure, clojurescript and why they're awesome at i t.a.k.e. unconference 2015

http://xkcd.com/{224,297}

Clojure & ClojureScript

Stefan Kanevhttp://skanev.com/@skanev

I.T.A.K.E. Unconf26 May 2015

Sofia

twitter: @skanev github: skanev blog: http://skanev.com/

Clojure from 10,000 feet

A modern LISP, hosted in the JVM, with a focus on concurrency

A modern LISP, hosted in the JVM, with a focus on concurrency

LISP: “that language with the parentheses”

also: a subculture

“LISP is too hip, even for me”

– a hipster

LISP

a * b + c * d

(+ (* a b) (* c d))

homoiconicitydata is code, code is

data

A modern LISP, hosted in the JVM, with a focus on concurrency

Sans the antiquities:car cdr lambda

Way better design

Less parentheses

A modern LISP, hosted in the JVM, with a focus on concurrency

Stable platform

Access to full Java ecosystem

Occasionally a huge P.I.T.A.

A modern LISP, hosted in the JVM, with a focus on concurrency

parallelism vs. concurrency

parallelism

Breaking a problem down to smaller parts that can be computed at the same time

concurrency

Synchronising a number of independent processes that are fighting for the same resources

Syntax

(func arg-1 arg-2 …)

(println "Hello world")

(+ 1 2)(< x y)

(+ 1 2 3 4 5 6)(< u v w x y z)

(+ (* a b) (* c d))

(+ (* a b) (* c d))

(defn say-hello [who] (println "Hello" who "!"))

(say-hello "Doctor")

OMG Parentheses!Or should I say:

((o) ((m)) (g) ( (( (( (( )) )) )) ))

Parentheses in LISP are not unlike metric time

(defn classify [age] (if (<= 13 age 19) "Teenager" "A normal person"))

(classify 18) ; "Teenager"

(defn factorial [n] (if (= n 1) 1 (* n (factorial (- n 1)))))

(defn fib [n] (cond (= n 0) 1 (= n 1) 1 :else (+ (fib (- n 1)) (fib (- n 2)))))

(fn [x] (* x 2))

(map (fn [n] (str "Mr. " n)) ["Anderson" "Bond" "Bean"])

; ("Mr. Anderson”; "Mr. Bond" ; "Mr. Bean")

(filter prime? (range 2 100))

; (2 3 5 7 11 13 17 19 23 29 31 37 41; 43 47 53 59 61 67 71 73 79 83 89 97)

(defn prime? [n] (not-any? (fn [x] (zero? (rem n x))) (range 2 (inc (Math/sqrt n)))))

Data Structures

maps (hashes)vectors (arrays)

sets

immutable

“Modifying” a structure creates a copy containing the change.

The original remains unmodified.

Y

simplicity

multicore ❤ immutable

persistent

The “originals” are maximally reused

a ! (3 2 1)

123

a

a ! (3 2 1)

a ! (3 2 1)b ! (conj a 4) (4 3 2 1)

123

a

a ! (3 2 1)b ! (4 3 2 1)

4b

5cc ! (conj a 5)

Hash Table

1020394597

1020205863

{:foo first, :bar second}

first

second

Hash Table

1020394597

1020205863

Hash Table

1020394597

1020205863

1021027443

(conj table :qux 1024)

not that simple

Vectors(“arrays” in other langs)

Vectors are represented by treesEach node has 32 children

log32…

…

…

… ⨯

O(?)

log32n

325 = 33 554 432

326 = 1 073 741 824

“essentially constant time”

Software Transactional Memory

concurrency 101

100 € +50 € ⨯2

How much money will the account have?

300 €250 €

100 €

+50 € = 150 €

x2 = 300 €

100 €

x2 = 200 €

+50 € = 250 €

100 €

200 €

150 €x2+50

100 €100 €

100 €

150 €

200 €

x2+50

100 €100 €

ref

state mutation is modelled as a transaction

if two transactions “get in each others’

way”, one of them will restart

(def account (ref 100))

; Thread 1 - Uncle Scrooge(dosync (alter account (fn [n] (* n 2))) (println "Scrooge: set to " @account))

; Thread 2 - Donald Duck(dosync (alter account (fn [n] (+ n 50))) (println "Donald: set to " @account))

100 €

300 €

150 €x2 +50100 €

100 €

X

x2150 €

Y

familiar

safe, easy, no deadlocks

Macros

Powerful instrument allowing expressive code

Also known as:the mother of all metaprogramming

MacroCodeSome other

code

doStuff();

Outputs on STDOUT. We want to have the result in a string instead.

PrintStream original = System.out;ByteArrayOutputStream output = new ByteArrayOutputStream();

try { PrintStream fileStream = new PrintStream(output); orgStream = System.out; System.setOut(fileStream);

doStuff();

} finally { System.setOut(original);}

String output = output.toString();

(do-stuff)

(with-out-str (do-stuff))

(with-out-str (do-stuff))

String output = withOutStr { doStuff();}

unless

(unless (hungry?) (sleep) (eat))

(if (not (hungry?)) (sleep) (eat))

(defmacro unless [condition consequent alternative] `(if (not ~condition) ~consequent ~alternative))

unless (isHungry()) { sleep();} else { eat();}

(cond (= n 0) 1 (= n 1) 1 :else (+ (fib (- n 2)) (fib (- n 1))))

(if (= n 0) 1 (if (= n 1) 1 (+ (fib (- n 2)) (fib (- n 1)))))

DSLDomain Specific Languages

Transparency

(source if-let)(source await)

ClojureScript

om

Very dynamic

DEMO

REPL Oriented Programming