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




Jede liste!

Prazna lista


> ()
() 


Aritmetika


> (+ 1 2)
3


Aritmetika


> (- 12 4)
8


Aritmetika


> (+ 1 2 3 4)
10


Aritmetika


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


Kako teče evaluacija?

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



    Clojure

    By strika

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    Od prazne liste do makroa

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