Not Everything is an Object

By Gary ShortGibraltar Software

What this Session is not…

• OO hating• Deep dive of Clojure• If you’ve written a Clojure App, you’ll probably

not learn anything.

What this Session is…

• Point out why OO dev is hard sometimes• Show you that there is an alternative• “It shouldn’t be this hard”.

4

Introduction

• Gary Short• Head of Gibraltar Labs– “Skunk Works” division of Gibraltar Software

• MVP C#– Python – NodeJS

• gary.short@gibraltarsoftware.com• @garyshort• Facebook.com/theOtherGaryShort

The Road to Here

http://www.flickr.com/photos/fyngyrz/

Ada Lovelace

• 1842 - 1843 Lovelace translated a memoir of an Italian mathematician on Charles Baggage’s newest proposed machine... the Analytical Engine. The article she wrote contained the entire specification of how to calculate Bernoulli numbers with the Engine. This is believed to be the first ever computer program.

The 1940s

• Then in the 1940’s along comes the first recognisable computers and we get programming languages to go with them...

• 1943 - Plankalkül (Konrad Zuse) • 1943 - Colossus• 1949 - C-10

The 1950s

• In the 1950s the first three modern programming languages whose descendants are still in widespread use today were designed:

• FORTRAN (1955), the "FORmula TRANslator", invented by John Backus et al.;

• LISP, the "LISt Processor", invented by John McCarthy et al.;

• COBOL, the COmmon Business Oriented Language, created by the Short Range Committee, heavily influenced by Grace Hopper.

More 1950s

• 1951 - Regional Assembly Language • 1952 - Autocode • 1954 - FORTRAN • 1954 - IPL (forerunner to LISP) • 1955 - FLOW-MATIC (forerunner to COBOL) • 1957 - COMTRAN (forerunner to COBOL) • 1958 - LISP • 1958 - ALGOL 58 • 1959 - FACT (forerunner to COBOL) • 1959 - COBOL

The 1960s

• 1962 - APL • 1962 - Simula • 1964 - BASIC • 1964 - PL/I

The 1970s

• 1970 - Pascal • 1970 - Forth • 1972 - C • 1972 - Smalltalk • 1972 - Prolog • 1973 - ML • 1975 - Scheme • 1978 - SQL

The 1980s

• 1983 - Ada • 1983 - C++ • 1985 - Eiffel • 1986 - Erlang • 1987 - Perl • 1989 - FL

The 1990s

• 1990 - Haskell • 1991 - Python • 1991 - Java • 1993 - Ruby • 1993 - Lua • 1994 - ANSI Common Lisp • 1995 - JavaScript • 1995 - PHP • 1997 - Rebol

Where we are Now

http://www.flickr.com/photos/gtarded/

What OOP/D is Good For

http://www.flickr.com/photos/gserafini/

What is it Not Good For?

http://www.flickr.com/photos/aloshbennett/

Also, we really suck at OOM…

Also hierarchies are brittle…

Also, OOPs get complex real fast…

The Solution

What Does it Mean to be Functional?

• First order functions• Function like constructs• Stateless• Immutable data

Clojure

• A Lisp• Dynamic• Functional– Impure

• “Lockless” Concurrency• Macros

• JVM• Java Interop• Fast• Persistent collections• Easy to learn.

Introduction to Clojure

• Java.Lang.Object• Arbitrary sized numbers• Ratios: 18/20• Nil is null and is treated as false

Persistent Collections

• Immutable– Cheap to copy

• Examples– (1 2 3)• List – sequential lookup time

– [1 2 3]• Vector – logarithmic lookup time

– {“key” 1, 3 7, “foo” “bar”}• Hashmap – unordered, key value pairs

Equality Vs Identity

• Equality– Two objects are equal• Two cylinders maybe equal if their volumes are equal

– Identity• Two pointers to the same object

– Clojure favours equality :-O

Clojure is Impure so has Mutability

• Var– Mutable pointer to immutable data• You can’t change the data• But you can change what data the var points to

• But vars hold global data, function defs etc .• This data won’t change• So why are vars mutable?• So we can patch running software.

The Reader

• Other programming languages– Compiler• Text -> lexing and parsing -> AST

• Clojure– The Reader• Text -> lexing and parsing -> Literals (Data)• As soon as it reads a complete literal it’s passed to...

The Evaluator

• Compile Phase– Traverses the data

• Symbol evaluation– Symbols evaluate into Vars

» Symbol Dog evaluates to a var in the current namespace» Symbol MyPets/Dog evaluates to var in namespace MyPets

• List evaluation– Lists evaluate into function calls

» (+ 1 2 3)

• Process macros

– Execute phase• Effects the special forms• Calls functions.

Special Forms

• Reserved symbol– Denotes special list evaluation

• Not a function call – it’s “something else”

• Def, if, do, let, quote, var, fn, loop, recur, throw, try, ., new, set!

• If a list starts with any of those it’s evaluated in a special way particular to that form

• (if condition a b?)• (if (been_drinking) (hungover) (happy))• (if (have_beers) (drink))

Let’s Talk About the ‘crazy’ Syntax

(prn “Hello World!”)

Maybe it’s not so Crazy

Console.WriteLine(“Hello World”)

Looping

Tail Recursion

http://www.flickr.com/photos/43911015@N05

34

Questions

• gary.short@gibraltarsoftware.com• @garyshort• Facebook.com/theOtherGaryShort