(intro "Clojure")

Matteo Barbieribarbieri.matteo@gmail.com

@matteobarbieri

?

Clojure is a dinamically-typed functional

language (LISP dialect) running as an hosted

language on the JVM (and JS) with a focus on

interactivity, immutability, no side effects,

laziness and concurrency

©2007 Rich Hickey

LISP dialect

lang=knparens

var people = [{name: "Matteo", age: 33},

{name: "Paolo", age: 25},

{name: "Luca", age: 55}];

people.filter(function isYoung(p) {

return p.age < 34;

}).map(function(p) {

return p.age;

}).reduce(function(a,b) {

return a + b;

},0);

13

(def people [{:name "Matteo" :age 33}

{:name "Paolo" :age 25}

{:name "Luca" :age 55}])

(defn young? [p] (< (:age p) 34))

(apply + (map :age (filter young? people)))

12

=12

=13

SIMPLE

SIMPLE MADE EASYhttps://www.infoq.com/presentations/Simple-Made-Easy

SIMPLE ≠ EASY

DIFFICULT → EASY

SIMPLE | COMPLEX

SIMPLE

if (x + y > 0) x else y

AST = Abstract Syntax Tree

if

cond elsethen

if

(x + y > 0) yx

if

> yx

x + y 0

if

> yx

+ 0

x y

if

> yx

+ 0

x y

if (x + y > 0) x else y

if

> yx

+ 0

x y

UNLESS

ANYONE?

unless (x + y > 0) y else x

if

> yx

+ 0

x y

unless

> xy

+ 0

x y

if

> yx

+ 0

x y

every tree is a list ()

first element is the root

other elements are children

recur

if

> yx

+ 0

x y

(if …)

if

> yx

+ 0

x y

(if (> …) x y)

if

> yx

+ 0

x y

(if (> (+ …) 0) x y)

if

> yx

+ 0

x y

(if (> (+ x y) 0) x y)

CODE AS DATA

HOMOICONICITY

immutability, no side effects,

laziness, concurrency etc.

INTERACTIVITY

REPLRead Evaluate Print Loop

DEMO