Clojure made simple - Lightning talk

( s im p le ( c lo ju r e ) ) C lo ju r e m a d e s im p le Ta l k

Clojure concepts Encourages Pure Functional approach - use STM to change state Functions as first class citizens - functions as arguments as they return a value Make JVM interoperation simple - easy to use your existing Java applications

A better Lisp ! Sensible () usage Sensible macro names JVM Interoperability

Which LISP is your wingman ? Common Lisp Clojure

The dark side of Clojure ( x )

The dark side of Clojure ( ( x ) )

The dark side of Clojure ( ( ( x ) ) )

The dark side of Clojure ( ( ( ( x ) ) ) )

The dark side of Clojure ( ( ( ( ( x ) ) ) ) )

...verses non-lisp languages ( ) == { ( ) };

Well nearly.... ([] ((()))) == { ( {( []) }) };

C o m p a r in g J a va w it h C lo ju r e

It s a ll b y t e c o d e in t h e e nd .. Any object in clojure is just a regular java object A reference type inheriting from: j ava. l ang. obj ec t

B a s ic C lo ju r e S yn ta x

Name-spaces ; Define a namespace ( ns nam s pac e- nam e- e) ; Include namespace code ( us e ' nam - s pac e- nam es e) Groups code together like a package statement in Java

Defining a function First principles Syntactic Sugar ( def nam e ( def n nam e ( f n [ ar gs ] [ ar gs ] ( f unc t i on- body ( f unc t i on- …) ) ) body . . . ) ) ( def n w c om m s age [ nam ] el e- es e ( pr i nt l n ( s t r “ W c om t o Cl oj ur e ” el e nam )e)

Special forms Special evaluation rules for the Clojure compiler - part of the language definition catch, def, do, dot ('.'), finally, fn, if, let, loop, monitor-enter, monitor-exit, new, quote, recur, set!, throw, try and var

Simple function example Define a simple function ( def n hel l o- w l d [ nam or e] ( pr i nt l n( s t r " Hel l o " nam ) ) e) Call the function in the REPL or in your code ( hel l o- w l d " j r 0c ket " ) or

Prefix notation ( def n s quar e- t he- number [ x] ( * x x) )

“Overloading” functions ( def n make ([ ] ; do t h e f o l l o wi n g f u n c t i o n i f n o ar g s ( s t r uc t vec t or 0 0) ) ( [ x y] ; d o i f x an d y ar e ar g u me n t s ( s t r uc t vec t or x y) ) )

Im m u t a b le D a ta s truc ture s

List – Ordered collection ( l i s t 1 3 5 7) ' ( 1 3 5 7) ( 1 2 3) ; 1 i s n o t a f unct i on

Vectors – hashed ordered list [ : m r i x- c har ac t er s [ : neo at : m pheus : t r i ni t y : s m t h] ] or i ( f i r s t [ : n e o : mo r p h e u s : t r i n i t y : s mi t h ] ) ( nt h [ : mat r i x : b ab yl o n 5 : f i r e f l y : s t ar g at e ] 2 ) ( c onc at [ : n e o ] [ : t r i n i t y] )

Maps – unordered key/values { : a 1 : b 2} { : a { : a 1} } { : a 1 , : b 2} {: a {: a 1}} { :a 1 :b } { { : a 1} : a} j ava. l an g . Ar r ayI n d e x Ou t Of Bo { { : a 1 } : a} u n d s Ex c e p t i o n : 3 ; i d i om - put : a on t he left { : a 1 : b 2} { : a 1 , : b 2}

L is t s a r e f o r c ode Ve c t o r s a r e fo r d a ta

Working with data (last [1 1 2 3 5 8]) (doc last) (defn penultimate [x] (last (butlast x)) ) (doc butlast) (penultimate [1 2 3 4 5])

And more... (nth [1 1 2 3 5 8] 2) (count [1 1 2 3 5 8]) (reverse [1 1 2 3 5 8]) (defn palindrome? [x] Proposition – naming (= x (reverse x)) ) convention

Even more (flatten [[1 1] 2 [3 [5 8]]]) (compress "aaaabccaadeeee") (encode "aaaabccaadeeee") (replicate 10 "a")

Defining a data structure ( def m dat a- s t r uc t ur e y- [ dat a ] ) ( def days - of - t he- week [ “Monday” “ Tues day” “W ednes day” ] )

Example data structure ( def j r 0c ket { : f i r s t - nam " J ohn" , e : l as t - name " St evens on" } )

c lo ju r e . org d o c s . c lo ju r e .o rg

All hail the REPL An interactive shell for clojure Fast feedback loop for clojure

M a n a g in g a c lo ju r e p r o je c t

Maven Just like any other Java project Step 1) Add Clojure library jar to your POM Step 2) Download the Internet !!!

le in in g e n Leiningen .o rg lein new Create a new clojure project lein deps Download all dependencies lein repl Start the interactive shell (repl) lein swank Start repl server

A fe w in t e r e s t in g C lo ju r e e x a m p le s

str (str h e l l o) Concatenate strings together represent a character using (def data “boo”) Join arguments with (str “message” data ) strings

Ratio Unique data type ( / 3 5) ( / 3. 0 Allow lazy evaluation 5) Avoid loss of precision (/ 1 3) (/ 1.0 3) (class (/ 1

Calling Java... ooooo!! ( j avax . s wi n g . JOp t i o n Pan e / s h o wMe s s ag e D i al o g n i l " He l l o W r l d " ) o

Importing Java into Clojure ( ns dr aw ng- dem i o ( : i m t [ j avax. s w ng J panel por i J Fr am e] [ j ava. awt Di m i on] ) ) ens

Working with Java Java Classes fullstop after class name ( J Fr am ) e. (Math/cos 3) ; static method call Java methods fullstop before method name ( . get Cont ent Pane f r am ;;method name first e) ( . f r am get Cont ent Pane) ;;object first e

What class is that... (class (str "Jr0cket")) java.lang.String (class (defn hello-world [name] (str "Hello cruel world"))) clojure.lang.Var

Clojure calling Java web stuff ( l et [ c onn] ( dot o ( Ht t pUr l Connec t i on. Ur l ) ( . s et Reques t M hod et “ POST” ) ( . s et DoOut put t r ue) ( . s et I ns t aneFol l ow Redi r ec t s t r ue) ) ] )

Recursive functions Functions that call Tail recursion themselves Avoids blowing the stack Fractal coding A trick as the JVM does not support tail recursion directly :-(

Tail recursion ( def n r ec ur s i ve- c ount er ( pr i nt ans w )er ( i f ( < ans w er 1000) ( r ec ur ( + ans wer 4) ) ) )

Where to find out more... c l oj ur e. or g/ c heat s h eet

Software Transactional Memory Provides safe, concurrent access to memory Agents allow encapsulated access to mutable resources

Functional for the web Big blog of stuff in > Big blob of stuff out Encourages modularising responsibilities Good at processing data in parallel

M o re to c o m e ... c l oj ur e. or g dev. c l oj ur e. or g @ r 0c ket j c l oj ur e. j r 0c ket . c o

Clojure made simple - Lightning talk

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