Getting' Clojure - '(parentheses are just hugs for your code)

'GETTING' CLOJURE'GETTING' CLOJURE'(PARENTHESES ARE JUST HUGS FOR YOUR CODE)'(PARENTHESES ARE JUST HUGS FOR YOUR CODE)

Created by / Jason Lewis Gary Trakhman

Javascript

function() return 5;

FUNCTIONSFUNCTIONS

Put some parens around it, kill the braces

(function() return 5; )

Change 'function' to 'fn', makes args into a vector

(fn [] return 5; )

Kill the 'return', last thing's always returned.

Welcome to Clojure.

(fn [] 5)

Move the left parenthesis over a bit more...

Done.

someFunction(arg1, arg2, arg3);

(someFunction arg1 arg2 arg3)

CALLING STUFFCALLING STUFF

THIS ISN'T AN ACCIDENTTHIS ISN'T AN ACCIDENTJavascript is 'Lisp in C's Clothing'Says Crockford: http://www.crockford.com/javascript/javascript.html

PUT ANOTHER WAY...PUT ANOTHER WAY...Q: Why do you think we've gotten so much mileage out ofjavascript?A: Lisp is very powerful, and it will never die

Should look familiar

Don't freak out

DON'T FREAK OUT

:key1 5, :key2 nil

[1 2 3 4 "five"]

[1 [2] #3 4 4 (constantly 5)]

=> (range 10)(0 1 2 3 4 5 6 7 8 9)

=> (take 11 (range))(0 1 2 3 4 5 6 7 8 9 10)

=> (last (range)) ;;Hope you don't mind waiting a long time.

DATADATA

Evals to...

;; semicolons are comments, commas are ignored,;; check out this weird hash­map:a­keyword 5,

"a string key" "a string value",

["a" :vector "acting" :as [:a :compound] "key"]

(fn [] "a no­arg functionthat returns this multi­line string,the function itself is the value"),

+ '(functions can be keys too, and whenyou quote symbols, you justhave symbols, not what they represent)

:a­keyword 5, "a string key" "a string value",["a" :vector "acting" :as [:a :compound] "key"]#<user$eval331$fn__332 user$eval331$fn__332@a585ef>,#<core$_PLUS_ clojure.core$_PLUS_@20a12d8f>(functions can be keys too and when you quote symbols you just have symbols not what they represent)

EVERYTHING IS DATAEVERYTHING IS DATA

ANYTHING CAN BE A KEY, BECAUSEANYTHING CAN BE A KEY, BECAUSE1. Every object is also a 'value'2. Values have true equality3. Values Never Change (Immutability)4. Without immutability, objects are just buckets in memory

...have you ever trusted a bucket with no values?

Q: Why is this big news?

A: I can write code and rest assured that other parts of myprogram can't change the data that I'm working on.

Q: But I thought every program is simply a short-lived httprequest handler that talks to a database? We just throw theprogram state out after every request!

A: Well, that's one way to do it.

http://www.ibm.com/developerworks/library/wa-aj-multitier2/

NODE.JS...NODE.JS...http://www.andrerodrigues.me/isel-

workshop/intro.html#/24

NODE.JS... IS NOTHING NEWNODE.JS... IS NOTHING NEWWe can write our own loopsNode.js assumes threaded programming is hard, andthrows out the baby with the bath-waterThreaded programming is hard without real 'Data' or'Values'Composition of any sort is simpler with data

APPROXIMATING NODE.JSAPPROXIMATING NODE.JS'Agents' are asynchronous queues, sharing threadpools todo work, storing the last value returned.

(defn inc­last [val] (conj val (inc (last val))))

;; We make a sequence of 10 inc­last tasks,;; then follow­up with a 'println' task(def tasks (concat (repeat 10 inc­last) [(fn [val] (println val) val)]))

;; starts off with a value of [0](let [a (agent [0])] (doseq [t tasks] (send a t)))

;; prints: [0 1 2 3 4 5 6 7 8 9 10]

Agents are not values, they are mutable references withasynchronous semanticsClojure has other mutable references types, acting as'containers' for values, for various use cases.Nothing prevents you from making your own.

(let [f (future (do­a­bunch­of­stuff))] ;; in another thread (do­stuff­in­this­thread) ;; return the value in f, blocking if it's not finished (deref f))

MORE!MORE!

Basically,Clojure promotes your ability to do whatever you want, bysimplifying things to their bare essence.

WHAT WE REALLY WANTWHAT WE REALLY WANTTools that let us

1. Compose Systems2. Change our minds3. Re-use components in different contexts, processes,

servers, etc..

Data/Values give us the ability to decouple things easily

'(code is data)

BRAINSPLODEBRAINSPLODE

Read-Eval-Print-Loop

(class (read­string "(+ 1 2)"));; clojure.lang.PersistentList

(map class (read­string "(+ 1 2)"));; (clojure.lang.Symbol java.lang.Long java.lang.Long)

R-E-P-LR-E-P-L1. Read: (read-string "(+ 1 2)") => '(+ 1 2)2. Eval: (eval '(+ 1 2)) => 33. What if there's something in the middle?

This is only the beginning

(defn only­even! [val] (if (and (integer? val) (odd? val)) (inc val) val))

(map only­even! (read­string "(+ 1 2)"));; '(+ 2 2)

(eval (map only­even! (read­string "(+ 1 2)")));; 4

Everybody likes chaining, right?

How is this implemented? Is this reusable?

$("#p1").css("color","red").slideUp(2000).slideDown(2000);

What if, as a library author, you could just not write that fluentinterface code at all?

(use 'clojure.string)

;; These are equivalent

(map trim (split (upper­case "hola, world") #","));; ("HOLA" "WORLD")

(­> "hola, world" upper­case (split #",") (­>> (map trim)));; ("HOLA" "WORLD")

Really useful when you're doing a lot of collection operations,filtering, etc.

(­>> (range) (filter even?) (map (partial * 2)) (take 10) (into []));; [0 4 8 12 16 20 24 28 32 36]

;; versus(into [] (take 10 (map (partial * 2) (filter even? (range)))))

1. I find the flat one easier to think about.2. Semantically equivalent.3. No burden on implementing code. Functions don't care

about how they're used.

Giving the user choices is more effective with more powerfullanguages. Leads to simple, composable libraries.

Let's look at a real one.

(defmacro lazy­seq "Takes a body of expressions that returns an ISeq or nil, and yields a Seqable object that will invoke the body only the first time seq is called, and will cache the result and return it on all subsequent seq calls. See also ­ realized?" :added "1.0" [& body] (list 'new 'clojure.lang.LazySeq (list* ':once true fn* [] body)))

;; simply returns a list, allocates a Java object (LazySeq) and wraps;; your expressions in a function

(macroexpand­1 '(lazy­seq ANYTHING1 ANYTHING2));; '(new clojure.lang.LazySeq (fn* [] ANYTHING1 ANYTHING2))

MACROSMACROS

Let's create an infinite sequence representing a square-wave --__--__--__--__

No mutable variables

(defn square­wave "t is the period for a half­cycle" [t] (letfn [(osc [cur­value so­far] (let [so­far (mod so­far t) next­val (if (zero? so­far) (­ cur­value) cur­value)] (cons next­val (lazy­seq (osc next­val (inc so­far))))))] (osc 1 0)))

(take 10 (square­wave 3));; (­1 ­1 ­1 1 1 1 ­1 ­1 ­1 1)

CALL TO ACTIONCALL TO ACTION1. Learn Clojure2. Build cool things3. Screencasts!

(You ruby guys really know how to make good screencasts)

DEMO TIMEDEMO TIMECLOJURE ON THE WEBCLOJURE ON THE WEB

Now clone this:

https://github.com/canweriotnow/bohjure

RESOURCESRESOURCESClojure: http://clojure.org

Fun Exercises: http://www.4clojure.comCheatsheets: http://clojure.org/cheatsheet

Building: https://github.com/technomancy/leiningenInsight: http://www.youtube.com/user/ClojureTV

Community docs: http://clojuredocs.orgBlogs: http://planet.clojure.in

Light Table: http://www.lighttable.comthis doc: http://gtrak.github.io/bohconf.clojure

MORE DEMO TIMEMORE DEMO TIME

THANKS FOR COMING!THANKS FOR COMING!WE ARE:WE ARE:

Gary Trakhman

Software Engineer at

@gtrakGT

Revelytix, Inc.

Jason Lewis

CTO at

@canweriotnow

An Estuary, LLC