Functional php

PHP funcional
além do
array_map
Jean Carlo Machado

Sobre
CompuFácil
⇢ php-src
⇢ git/git
⇢ torvald/linux
⇢ vim/vim
⇢ Doctrine
⇢ Zend Framework
⇢ phpunit

1950: Estruturado
subrotinas: while, for, if
GOTO

Programação
Funcional
mudança de estado

Vantagens
Concorrência nativa
Facilita a modularização
Desacelera o apodrecimento

Estado === Impureza
$inpureIncrement = function (&$count) {
$count++;
};
for ($i = 0; $i < 3; $i++) {
echo "Next:".$inpureIncrement($i);
}
//Next: 0
//Next: 2
//Next: 4

Pureza (relativa)
function pureIncrement($count) {
$myCounter = $count;
$inpureIncrement = function(&$myCounter){
$myCounter++;
};
$inpureIncrement($myCounter);
return $myCounter;
}
//Next: 1
//Next: 2
//Next: 3

Impuros por
natureza
IO
random

Retornáveis
$sumPartial = function(int $a) {
return function(int $b) use ($a) {
return $a+b;
}
};
$sumOne = $sumPartial(1);
$sumOne(7);
//8
$sumOne(5);
//6

Repassáveis
$incrementTwo = function ($n, $sumOne) {
return $sumOne($sumOne($n));
};

Deﬁna o básico
function sum($a, $b) {
return $a + $b;
}
//function product($a, $b);
//function aORb($a, $b);
//function append($a, $b);
//function greater($a, $b);

Componha
$sumList = fold('sum', 0, [1,2,3]);
//6
$multiplyList = fold('product', 1, [2,2,2]);
//8

function fold(
callable $f,
$init,
$list) {
if (empty($list)) {
return $init;
}
return $f(
fold($f, $init, allbutlast($list)),
last($list)
);
};

Map
$double = function($a) {
return $a*2;
}
$map($double, [1, 2, 4]));
//[2,4,8]

$map = function($f, $list) {
$applyAndAppend=function($f,$list,$b){
$list[] = $f($b);
return $list;
};
return fold($applyAndAppend,null)($list);
}

Árvores
$tree = [
1 => [
2,
3 => [
4,
],
]
];
foldTree($sum, $sum, 0, $tree)
//10

Map Tree
$tree = [
3 => [1,4],
1 => [1,5 => [1,2,3]]
];
$result = mapTree($double, $tree);
//[
// 6 => [2,8],
// 2 => [2,10 => [2,4,6]]
//];

PHP functions
⇢ array_map
⇢ array_ﬁlter
⇢ array_reduce
⇢ array_sum
⇢ array_unique

g (f input)
⇢ começa f só quando g tenta ler algo
⇢ suspende f
⇢ g roda até precisar ler mais dados

Nth primes
getNthPrimes(10);
//[1,2,3,5,7,11,13,17,19,23]

Nth primes
function primes() {
foreach (finfiniteSequence(1) as $i) {
if (isPrime($i)) {
yield $i;
}
}
}
print_r(ftakefrom(primes(), 10));
//[1,2,3,5,7,11,13,17,19,23]

function isPrime($x) {
$seq = ftakeFrom(
finfiniteSequence(),
$x
);
$seq = fremoveFirst($seq);
$seq = fremoveLast($seq);
$multiple = function($a) use ($x) {
return ($x % $a == 0);
}
return fnoneTrue(
fmap($multiple, $seq)
);

Aplicação parcial
$append3 = function($a, $b, $c) {
return [$a, $b, $c];
};
$append1And2 = fpartial($append3)(1)(2);
$append1And2(5)
//[1,2,5]
$append1And2(9)
//[1,2,9]

function partial(
callable $callable, ...$args){
$arity = (new ReflectionFunction(
$callable
))
->getNumberOfRequiredParameters();
return $args[$arity - 1] ?? false
? $callable(...$args)
: function (...$passedArgs)use($callable,
return partial($callable,
...array_merge($args, $passedArgs)
);
};

Requisito v1
curl http://localhost:8000/profile/777
#{"id":777,"name":"Saruman"}

function getProfile(
callable $query,
$userId) {
return $query(
"Select * from User where id = %id ",
$userId
);
}
$realProfile = fpartial
('getProfile')
([new Database, 'query']);

Requisito v2:
cache
# go to database
# don't go to database

$memoize = function($func) {
static $results = [];
return function ($a) use (
$func, &$results) {
$key = serialize($a);
if (empty($results[$key])){
$results[$key]=call_user_func(
$func, $a );
}
return $results[$key];
};};
$memoizedProfile = $memoize($realProfile);

Requisito v3: log
request
# also writes to file
cat /tmp/log
#getProfile called with params s:3:"777";

function fileLogger($str) {
file_put_contents(
'/tmp/log',
"FileLog: ".$str.PHP_EOL,
FILE_APPEND
);
}

function logService(
$logger, $serviceName,
callable $service) {
return function($args) use (
$logger, $serviceName,
$service) {
$logger(
"Service called ". $serviceName.
" with params ".serialize($args));
return call_user_func($service, $args);
};
};

$loggedMemoizedGetProfile =
fpartial('logService')
($logger)
('getProfile')
($memoizedProfile);

Modularização
Mais que módulos
Decompor os problemas em partes menores
Re-compor com avaliação tardia e funções de alta
ordem

Apodrecimento
⇢ Difícil adicionar efeitos sem quebrar as interfaces
⇢ Quão maior a interface mais feio o código
⇢ Interfaces facilmente quebráveis com composicão
⇢ Quebrar encoraja reúso
⇢ Complexidade horizontal ao invés de vertical

Imperativo quando necessário
Funcional quando possível

Para novos tipos
1 - deﬁna as operações fundamentais
2 - junte funções

Seu trabalho não é resolver problemas
Deﬁnir problemas de uma forma que
eles se resolvam

Ferramentas
⇢ hlstrojny/functional-php
⇢ functional-php/pattern-matching
⇢ jeanCarloMachado/f
⇢ pimple/pimple

Referências
⇢ Why functional programming matters
⇢ http://archive.li/uTYWZ#selection-407.912-407.919
⇢ https://medium.com/@jugoncalves/functional-programming-
should-be-your-1-priority-for-2015-47dd4641d6b9
⇢ https://blog.inf.ed.ac.uk/sapm/2014/03/06/enemy-of-the-
state-or-why-oop-is-not-suited-to-large-scale-software/
⇢ https://www.youtube.com/watch?v=7Zlp9rKHGD4
⇢ https://www.youtube.com/watch?v=q0HRCEKAcas

Dúvidas?
Github: https://github.com/jeanCarloMachado
Twitter: https://twitter.com/JeanCarloMachad
E-mail: contato@jeancarlomachado.com.br

Functional php

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