FUNCTIONAL PHP SIMON HOLYWELL 12/02/2014 0 

WHO? Lead developer Mosaic in Brighton Full service agency @ on Twitter Treffynnon SimonHolywell.com 

WORK Web apps Obligatory CMS! 

PROJECTS Maintainer of ssdeep - and extension - geo library for PHP - Node.js bot for GTalk - now defunct :( Idiorm and Paris PECL HHVM Navigator PHP-at-Job-Queue-Wrapper njsbot 

FUNCTIONS IN PHP Rarely employed Discouraged by PHP's evolution Naming collisions The old name spacing object 

SIMPLE BEASTS PHP functions are: Easy Contained Unaware of global state Can now be namespaced 

FUNCTION < ? p h p f u n c t i o n h e l l o ( $ a r g = ' W o r l d ' ) { e c h o _ _ F U N C T I O N _ _ . " $ a r g " ; } h e l l o ( ) ; / / h e l l o W o r l d 

A LITTLE BIT OF HISTORY I started with PHP3 Functions were the norm Classes merely wrapped them OOP was very poorly understood 

DRY Most mashed code with HTML Functions promoted code reuse HTML then had functions in it! 

EVOLVE Come PHP4 you get better OOP Functions no longer in focus They become seen poorer cousins Can't carry context vs. class properties 

PHP5 Functions are still marginalised Still seen as spaghetti The bad way 

PHP5.3+ Proper anonymous functions We get closures! 

THE BASICS ARE IN PLACE ¡Functional is possible! 

JUST WHAT IS FUNCTIONAL? Programming without assignment Stateless Pure 

WITHOUT ASSIGNMENT... Say goodbye to $ v a r = ' v a l u e ' ; $ C l a s s I n s t a n c e - > p r o p e r t y = ' v a l u e ' ; 

STATELESS AND PURE No: Globals Side effects Incrementors/accumulators For, while or foreach loops 

PASSING VALUES From function to function as Arguments Return values 

10 How would you sum all the integers from one to ten? 

IMPERATIVE WAY < ? p h p $ s u m = 0 ; f o r ( $ i = 1 ; $ i < = 1 0 ; $ i + + ) { $ s u m + = $ i ; } / / $ s u m = 5 5 

FUNCTIONAL WAY < ? p h p a r r a y _ s u m ( r a n g e ( 1 , 1 0 ) ) ; More descriptive Removes state ($ s u m ) Reusable components 

LIKE WELL-DESIGNED OOP Encapsulated Broken down into small chunks Reusable 

CAN IT BE NEATER? < ? p h p a r r a y _ s u m ( r a n g e ( 1 , 1 0 ) ) ; Lua - s = 0 ; f o r i = 1 , 1 0 d o s = s + i e n d Erlang - l i s t s : s u m ( l i s t s : s e q ( 1 , 1 0 ) ) . Clojure - ( r e d u c e + ( r a n g e ( i n c 1 0 ) ) ) Ruby - ( 1 . . 1 0 ) . i n j e c t ( 0 ) { | s , i | s + i } Python - s u m ( r a n g e ( 1 , 1 0 + 1 ) ) F# - L i s t . s u m [ 1 . . 1 0 ] Scala - ( 1 t o 1 0 ) . s u m Haskell - s u m [ 1 . . 1 0 ] 

THE SCALE Pure - Haskell Middle ground - Scala and Clojure Dabbling - PHP and Python Hopeless - Brainfuck % 

HISTORY Vienna Circle - 1920s Philosophers Logic Can be defined apart from content Unless experienced or observed = worthless M! = ethics, metaphysics, religion and aesthetics 

KURT GÖDEL Attended Vienna Circle Ultimately disproved manifesto Incompleteness theorem - 1931 Some truths cannot be proven 

FUNCTIONAL HISTORY Kurt Gödel - recursively calculated functions - 1930s Haskell Curry - combinatory logic - 1927 Alan Turing - machines calculating from inputs - 1936 Alonzo Church - lambda calculus - 1930s 

LAMBDA CALCULUS Mathematical functions - abstraction Accept functions as parameters Return other functions Basis of functional programming 

COMBINATORY LOGIC Haskell Curry Combinatory calculus - 1927 Primitive functions combined to build others Named after him Currying Haskell 

WORLD WAR II Vienna/Göttingen unsafe Great minds move to US or UK Turing involved in code breaking 

ACADEMIC Little activity 'til late 1950s 

LISP 1958 Jon McCarthy MIT Became the standard for AI 

MOMENTUM Some advances Still mostly academic Imperative programming the norm 

TELEPHONES Fault tolerant system Erlang by Ericsson 1980s 

ERICSSON Ericsson Erlang Highly symbolic to improve productivity Lisp and Prolog discounted Focused on Reliability Concurrency 

HASKELL Formed by committee Pure functional language 

COMMERCIAL ADOPTION Domain specific languages (DSL) Type handling Pattern matching Fast to build complex parsers Less code = easier to maintain 

CASESTUDY Barclays bank Functional Payout Framework Written in Haskell DSL for mathematicians Builds trading applications Functional eased scope creap ^ 

NONE SHALL PASS! < ? p h p $ a l l o w a b l e _ i p s = a r r a y ( ' 1 9 2 . 1 6 8 . 0 . ' , ' 8 . 8 . 8 . 8 ' , ) ; a r r a y _ f i l t e r ( $ a l l o w a b l e _ i p s , f u n c t i o n ( $ i p ) { r e t u r n $ i p = = s u b s t r ( $ _ S E R V E R [ ' R E M O T E _ A D D R ' ] , 0 , s t r l e n ( $ i p ) ) ; } ) ? : d i e ( ' D e n i e d . ' ) ; 

ARRAY_FILTER() < ? p h p a r r a y _ f i l t e r ( $ a l l o w a b l e _ i p s , f u n c t i o n ( $ i p ) { Takes a list and predicate "Removes" items when predicate fails λ or anonymous function And hey, it's not a loop! 

THA PREDICATE < ? p h p f u n c t i o n ( $ i p ) { r e t u r n $ i p = = s u b s t r ( $ _ S E R V E R [ ' R E M O T E _ A D D R ' ] , 0 , s t r l e n ( $ i p ) ) ; } IP v.4 addresses Chops user IP to same length as allowable ($ i p ) Compares result for equality 

KILLER CONDITION < ? p h p ? : d i e ( ' D e n i e d . ' ) ; Empty arrays == false Terminates application Ternary shortcut < ? p h p e x p r 1 ? e x p r 2 : e x p r 3 ; e x p r 1 ? : e x p r 3 ; 

WHAT SAY THE BLACK KNIGHT? < ? p h p / / $ _ S E R V E R [ ' R E M O T E _ A D D R ' ] = ' 1 9 2 . 1 6 8 . ' $ a l l o w a b l e _ i p s = a r r a y ( ' 1 9 2 . 1 6 8 . 0 . ' , ' 8 . 8 . 8 . 8 ' , ) ; a r r a y _ f i l t e r ( $ a l l o w a b l e _ i p s , f u n c t i o n ( $ i p ) { r e t u r n $ i p = = s u b s t r ( $ _ S E R V E R [ ' R E M O T E _ A D D R ' ] , 0 , s t r l e n ( $ i p ) ) ; } ) ? : d i e ( ' D e n i e d . ' ) ; 

BONUS: ARRAY CLEANER a r r a y _ f i l t e r ( ) without a predicate Entries == false dropped false == "" == 0 == array() == null == '0' == 0.0 < ? p h p a r r a y _ f i l t e r ( a r r a y ( ' ' , ' s ' , 0 ) ) ; / / a r r a y ( ' s ' ) 

BENEFITS OF FUNCTIONAL Techniques useful for OOP Abstraction = more readable No distracting guff Just the problem solving stuff 

...AND MORE Shorter code = quicker to debug No global state to assemble in mind Focus on the hard problems 

HEY! WAIT THERE'S STILL MORE Testing is easier No globals again Values are final 

REFERENTIAL TRANSPARENCY Replace any function with it's return value Algorithm still works! < ? p h p a r r a y _ s u m ( a r r a y ( 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 1 0 ) ) ; / / I s s t i l l 5 5 ! Can you do that to a for loop? 

NO! < ? p h p $ s u m = 0 ; f o r ( $ i = 1 ; $ i < = 1 0 ; $ i + + ) { $ s u m + = $ i ; } / / $ s u m = 5 5 Closest: < ? p h p $ s u m = 0 ; $ s u m + = 1 ; $ s u m + = 2 ; . . . $ s u m + = 1 0 ; / / $ s u m = 5 5 

SO WHAT ELSE? Easier parallel processing Who's using the other cores in your CPU? Not common in PHP - see pthreads 

IF PHP WERE REALLY FUNCTIONAL Machine optimisation of code Lazy-evaluation Hot code deployment (Erlang!) % 

STEP BACK - Λ λ lambda function anonymous function < ? p h p $ f u n c _ n a m e = f u n c t i o n ( $ p a r a m ) { r e t u r n $ p a r a m ; } ; 

SHOULD BE FAMILIAR < ? p h p s p l _ a u t o l o a d _ r e g i s t e r ( f u n c t i o n ( $ c l a s s ) { i n c l u d e ' c l a s s e s / ' . $ c l a s s . ' . c l a s s . p h p ' ; } ) ; If not - how about in JS: b u t t o n . o n c l i c k = f u n c t i o n ( ) { a l e r t ( ' L a m b d a ' ) ; } ; 

EXTEND IT - CLOSURE Just like a lambda But, with context/data ($ v a l u e ) < ? p h p $ v a l u e = 5 ; $ f u n c _ n a m e = f u n c t i o n ( $ p a r a m ) u s e ( $ v a l u e ) { r e t u r n $ p a r a m + $ v a l u e ; } ; e c h o $ f u n c _ n a m e ( 3 ) ; / / 8 Vars can be other closures or lambdas too No aliasing unfortunately 

MAP a r r a y _ m a p ( ) Applies function to each element Returns new array with adjusted elements < ? p h p a r r a y _ m a p ( f u n c t i o n ( $ v ) { r e t u r n s t r t o u p p e r ( + + $ v ) ; } , $ a r r a y ) ; a r r a y ( ' o ' , ' g ' , ' o ' ) becomes a r r a y ( ' P ' , ' H ' , ' P ' ) 

SOCHI MAP IT 1st 

APPLIED BY A MAP 2nd 

MORE MAPPING! 3rd 

REDUCE a r r a y _ r e d u c e ( ) Fold array down to one value Applies function to each element < ? p h p a r r a y _ r e d u c e ( $ a r r a y , f u n c t i o n ( $ r e s u l t , $ v ) { r e t u r n $ r e s u l t . = $ v ; } ) ; a r r a y ( ' o ' , ' g ' , ' o ' ) becomes o g o 

REDUCE FIGURES 9 + 6.10 + 7.62 + 6.98 ... 

FOLDING SCORES 15.10 + 7.62 + 6.98 ... 

DISAPPOINTMENT 63.10 

MAP AND REDUCE Combined to great effect < ? p h p $ a = a r r a y ( ' o ' , ' g ' , ' o ' ) ; a r r a y _ r e d u c e ( a r r a y _ m a p ( f u n c t i o n ( $ v ) { r e t u r n s t r t o u p p e r ( + + $ v ) ; } , $ a ) , f u n c t i o n ( $ r e s u l t , $ v ) { r e t u r n $ r e s u l t . = $ v ; } ) ; / / P H P 

RECURSION Just like the meaning of PHP A function that calls itself Directly or Indirectly Can be used for loops Loose or forgotten condition = blown stack 

HEADS OR TAILS PHP = heads < ? p h p f u n c t i o n h e a d _ s u m ( $ x ) { r e t u r n ( $ x = = 1 ) ? $ x : $ x + h e a d _ s u m ( $ x - 1 ) ; } h e a d _ s u m ( 1 0 ) ; / / 5 5 Other languages have optimised tails 

HIGHER ORDER FUNCTIONS Functions that have other functions as Call parameters Return values Can be used to form expressions 

HIGHER EXAMPLE < ? p h p $ d a t a = a r r a y ( 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 1 0 ) ; f u n c t i o n g e t _ a l g o r i t h m ( $ r a n d _ s e e d _ f n c ) { r e t u r n ( o d d _ e v e n ( $ r a n d _ s e e d _ f n c ( ) ) ) ? f u n c t i o n ( $ v a l u e ) { r e t u r n $ v a l u e * $ v a l u e ; } : f u n c t i o n ( $ v a l u e ) u s e ( $ r a n d _ s e e d _ f n c ) { r e t u r n ( $ v a l u e * $ v a l u e / $ r a n d _ s e e d _ f n c ( ) ) + 1 0 ; } ; } f u n c t i o n o d d _ e v e n ( $ v a l u e ) { r e t u r n ( $ v a l u e % 2 = = = 0 ) ; } $ r a n d _ s e e d _ f n c = f u n c t i o n ( ) { r e t u r n r a n d ( ) ; } ; $ r e s u l t s = a r r a y _ m a p ( g e t _ a l g o r i t h m ( $ r a n d _ s e e d _ f n c ) , $ d a t a ) ; 

PARTIAL FUNCTION APPLICATION Essentially set defaults < ? p h p $ f i r s t _ c h a r = f u n c t i o n ( $ s t r i n g ) { r e t u r n s u b s t r ( $ s t r i n g , 0 , 1 ) ; } ; Works nicely with a r r a y _ m a p ( ) < ? p h p a r r a y _ m a p ( $ f i r s t _ c h a r , a r r a y ( ' f o o ' , ' b a r ' , ' b a z ' ) ) ; / / a r r a y ( ' f ' , ' b ' , ' b ' ) 

CURRYING Each parameter becomes a function More flexible PFA < ? p h p $ f i r s t _ c h a r = f u n c t i o n ( $ s t a r t ) { r e t u r n f u n c t i o n ( $ l e n g t h ) u s e ( $ s t a r t ) { r e t u r n f u n c t i o n ( $ s t r i n g ) u s e ( $ s t a r t , $ l e n g t h ) { r e t u r n s u b s t r ( $ s t r i n g , $ s t a r t , $ l e n g t h ) ; } ; } ; } ; $ a = $ f i r s t _ c h a r ( 0 ) ; $ b = $ a ( 1 ) ; $ b ( ' f o o ' ) ; / / f $ c = $ a ( 2 ) ; $ c ( ' f o o ' ) ; / / f o 

MEMOIZATION Function local cache < ? p h p f u n c t i o n d e m o ( ) { s t a t i c $ _ c ; i f ( i s _ n u l l ( $ _ c ) ) { $ _ c = g e t _ s o m e _ e x p e n s i v e _ o p e r a t i o n ( ) ; } r e t u r n $ _ c ; } Handy in class methods too! 

WHEN TO USE FUNCTIONAL? Practice Innate understanding Turing complete methodology 

SO MUCH MORE... Function composition Tail recursion Function objects New language features Functors Applicatives Monads Event driven programming Null handling & more. 

EXIT() Functional PHP Follow @ for tips Simon Holywell Follow @ FunctionalPHP FunctionalPHP.com Treffynnon SimonHolywell.com