Functional Programming in Clojure

SoCal Code Camp 12+13 November 2016

Functional Programming in Clojure

Troy Miles• Troy Miles aka the RocknCoder

• Over 37 years of programming experience

• Speaker and author

• Author of jQuery Essentials

• bit.ly/rc-jquerybook

• rockncoder@gmail.com

• @therockncoder

Build Mobile Apps!

• Develop mobile apps with Ionic and AngularJS

• Learn the Ionic CLI

• Fetch data via ajax

• Deploy your app to Android & iOS

• bit.ly/ionicvideo

Slides Online

• http://www.slideshare.net/rockncoder/functional-programming-in-clojure-68544774

Our Agenda• Clojure?

• Lisp

• The Java Virtual Machine

• Leiningen

• Functional Programming

Clojure?

–Paul Graham

“Lisp is worth learning for the profound enlightenment experience you will have when you finally get it; that experience will make you a better programmer for the rest of your days, even if you never actually use Lisp itself a lot.”

What is Clojure?

• A dynamic, general-purpose programming language

• A Modern Lisp

• Designed to be hosted

• Functional, but practical

Other Hosts for Clojure

• ClojureScript - Compiles to JavaScript

• Clojure CLR - Compiles to IL, for Microsoft’s CLR

ClojureScript

• Clojure + ClojureScript used together by 66% of the community

• Om / Reagent - Interfaces for Facebook’s React Library

• Mori - ClojureScript’s Immutable data structure for vanilla JavaScript

Companies using Clojure• Walmart Labs

• Puppet Labs

• ThoughtWorks

• Amazon

• Facebook

• Groupon

• Intuit

• Salesforce

• Zendesk

–Paul Graham

“I suppose I should learn Lisp, but it seems so foreign.”

Lisp? Lisp!

• Created in 1958 by John McCarthy

• Second oldest high-level language still in use today

• Influenced by Alonzo Church’s lambda calculus

• A family of languages including: Common Lisp, Scheme, Emacs Lisp

Lisp Innovations• recursive function

• dynamically allocated memory

• garbage collection

• lexical closures

• macros

The Java Virtual Machine• An abstract computing machine that allows a

computer run a Java program

• Type system

• Garbage collection

• Threads

• Just-in-time compiler (JIT)

• Favorite target of criminal hackers

JVM Languages• Ceylon - Java competitor from Red Hat

• Groovy - OOP langage

• JRuby - Ruby on the JVM

• Jython - Python on the JVM

• Kotlin - Java competitor from JetBrains

• Rhino/Nashorn - JavaScript engines

• Scala - OOP / Functional language

Build Tools

• Apache Maven

• Leiningen

Leiningen

• A tool for automating Clojure projects

• Written in Clojure

• Open source and maintained by a large community

• A play on another famous build tool, Apache Ant

Using Leiningen

• Searches from repos

• lein new app my-stuff

Directory├── CHANGELOG.md ├── LICENSE ├── README.md ├── doc │   └── intro.md ├── project.clj ├── resources ├── src │   └── my_app │   └── core.clj └── test └── my_app └── core_test.clj

Editors / IDEs

• Emacs - created in 1976

• Vim - created in 1991

• Eclipse + Counterclockwise - created in 2001

• Intellij IDEA + Cursive - created in 2001

What is Functional Programming?

Key Functional Features• Pure functions

• First-class / High order functions

• Immutable data

• Recursion

• Referential transparency

Functional vs. Imperative

what? functional imperative

primary construct function class instance

state change bad important

order of execution not important important

flow control function calls recursion

loops, conditionals, method calls

Sample Languagesmostly functional mixed mostly imperative

Lisp/Scheme JavaScript Java

ML Scala C#

Haskell Python C++

Clojure Dart Swift

F# Lua Ruby

Erlang R Kotlin

Pure Functions

• Must return a value

• Must accept at least one argument

• Can’t produce any side-effects

• Must return the same output for a given input

Pure Functions Are Super

• Cacheable

• Portable

• Self-documenting

• Testable

• Reasonable

First-Class Functions

• Assigned to variables

• Stored in arrays

• Passed as arguments to other functions

• Returned from functions

Higher-Order Functions

• Accept other functions as parameter

• And/or return a function

• Allows for the creation of function factories

• This is the core of the curry function

Code Samples

1 (function () { 2 'use strict'; 3 const fizzBuzz = function () { 4 for (let i = 1; i <= 100; i += 1) { 5 let printVal = i + ' '; 6 if (i % 3 === 0) { 7 printVal += 'Fizz'; 8 } 9 if (i % 5 === 0) { 10 printVal += 'Buzz'; 11 } 12 console.info(printVal); 13 } 14 }; 15 fizzBuzz(); 16 }());

FizzBuzz in JavaScript

FizzBuzz in Clojure1 (defn fizzbuzz [start finish] 2 (map (fn [n] 3 (cond 4 (zero? (mod n 15)) "FizzBuzz" 5 (zero? (mod n 3)) "Fizz" 6 (zero? (mod n 5)) "Buzz" 7 :else n)) 8 (range start finish))) 9 10 (fizzbuzz 1 100)

Links• Clojure - http://clojure.org/

• ClojureScript - http://clojurescript.org/

• ClojureCLR - http://clojure.org/about/clojureclr

• Clojure Docs - http://clojure-doc.org/

• Try Clojure - http://www.tryclj.com/

More Links• Om - https://github.com/omcljs/om

• Reagent - https://reagent-project.github.io/

• Mori - https://github.com/swannodette/mori

• Clojure/Android - https://github.com/clojure-android

• Leiningen - http://leiningen.org/

And Even More Links

• SICP Online - http://web.mit.edu/alexmv/6.037/sicp.pdf

• Paul Graham - http://paulgraham.com/avg.html

Summary

• Clojure is functional language on the JVM

• It is interoperable with Java

• It has a Lisp syntax which is not

–Edsger Dijkstra

“Object-oriented programming is an exceptionally bad idea which could only have

originated in California.”