Clojure

Od prazne liste do makroa

Nebojša Stričević

5. decembar 2013.

Clojure

• pojavio se 2007.
• pripada familiji LISP jezika
• 1958. - prvi LISP

Clojure i zagrade

(defn- fib-iter
  [max n i j]
  (if (= n max)
   j
   (recur max
    (inc n)
    j
    (+ i j))))
 

Upozorenje

malo ću vas lagati

Clojure Reader

Prazna lista

> ()
() 

Aritmetika

> (+ 1 2)
3

Aritmetika

> (- 12 4)
8

Aritmetika

> (+ 1 2 3 4)
10

Aritmetika

> (* (- 12 8) (+ 1 2))
12

Evaluacija

> (* (- 12 8) (+ 1 2))
; (* 4 (+ 1 2))
; (* 4 3)
12

Promenljive

> (def a 3)
a
> (def b 4)
b
> (println a)
3
> (+ a b)
7

Funkcije

> (def add-2
    (fn [n]
      (+ n 2)))
add-2

> (add-2 4)
6

Funkcije

>(def more-than-5?
   (fn [n]
     (if (> n 5)
       (println "Yes!")
       (println "No...")))
more-than-5?

> (more-than-5? 2)
"No..."

Liste

> (def numbers (1 2 3 4 5))

Error! There is no function "1".

Liste

> (def numbers '(1 2 3 4 5))
numbers

Operacije sa listama

> (def numbers '(1 2 3 4 5))
numbers
> (first numbers)
1
> (rest numbers)
(2 3 4 5)

> (cons 0 numbers)
(0 1 2 3 4 5)

Operacije sa listama

> (def numbers '(1 2 3 4 5))
numbers

> (map add-2 numbers)
(3 4 5 6 7)

Šta možemo stripati u listu?

> (def code '(+ 1 2))
code

> (println code)
(+ 1 2)

> (eval code)
3

Code as data

> (def code '(+ 1 2))
code

>(def new-code
   (cons '- (rest code)))
new-code

> (println new-code)
(- 1 2)

> (eval new-code)
-1

Code as string

• Ruby
• Python
• JavaScript
• ...

 eval "1 + 2"

Proširivanje jezika

(if (= 1 1)
  (println "1 is indeed 1"))

(unless (= 1 1)
  (println "1 is not 1"))

unless je funkcija!

> (def unless
    (function [condition code]
      (if (not condition)
        code)))

> (unless (= 1 1)
    (println "1 is not 1"))

 "1 is not 1"

unless je makro

(defmacro unless [condition code]
  '(if (not ~condition)
    ~code))

> (unless (= 1 1)
    (println "1 is not 1"))

> (if (not (= 1 1))
    (println "1 is not 1"))

>

Java?

// 1996.
for (int i = 0; i < collection.size(); i++) {
    SomeType var = collection.get(i);
    ...
}

// 2004.
for (SomeType var : collection) {
    ...
}

Clojure

(defmacro foreach [[sym coll] & body]
  `(loop [coll# ~coll]
    (when-let [[~sym & xs#] (seq coll#)]
      ~@body
      (recur xs#))))


>(foreach [i numbers]
   (println i))

Zašto Clojure?

• Lisp
• Functional Programming
• designed for Concurrency
• JVM
• Java interoperability
  

Hvala

http://slid.es/strika/clojure