Functional approach in software design

Functional programming is a paradigm known for decades. It is gaining popularity again, due to the rise of purely functional languages like Haskell. You may wonder, how it could be useful in PHP? Using a few techniques and a slight change of perspective you will be able to write code that is cleaner and easier to understand. You will be able to design and implement huge solutions by composing them from small and well-tested parts.

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1. functional approach in software design Tomasz Kowalczyk @tmmx
4. introduction
5. purpose
6. levels
7. level 0: approach
8. paradigm shift
9. SOLID
10. immutability
11. higher order functions
12. composition
13. level 1: operations
14. casual conditionals
15. $result = []; foreach($this->users as $user) { if($user->isDisabled()) { continue; } if($user->isHidden()) { continue; } $result[] = $user; } return $result;
16. $result = []; foreach($this->users as $user) { if($user->isDisabled()) { continue; } if($user->isHidden()) { continue; } $result[] = $user; } return $result;
17. $isEnabled = function(User $u): bool { return false === $u->isDisabled(); }; $isVisible = function(User $u): bool { return false === $u->isHidden(); }; return array_filter( array_filter($this->users, $isVisible), $isEnabled);
18. $isEnabled = function(User $u): bool { return false === $u->isDisabled(); }; $isVisible = function(User $u): bool { return false === $u->isHidden(); }; return $this->users ->filter($isVisible) ->filter($isEnabled);
19. endless loops
20. $ids = []; foreach($this->users as $user) { foreach($user->getTags() as $tag) { $tagId = $tag->getId(); if(false === in_array($tagId, $ids, true)) { $ids[] = $tagId; } } } return $ids;
21. $ids = []; foreach($this->users as $user) { foreach($user->getTags() as $tag) { $tagId = $tag->getId(); if(false === in_array($tagId, $ids, true)) { $ids[] = $tagId; } } } return $ids;
22. $userToTags = function(User $user): array { return $user->getTags(); }; $tagToId = function(Tag $tag): int { return $tag->getId(); }; return array_unique(array_map($tagToId, array_merge( ...array_map($userToTags, $this->users) )));
23. $userToTags = function(User $user): array { return $user->getTags(); }; $tagToId = function(Tag $tag): int { return $tag->getId(); }; return $this->users ->flatMap($userToTags) ->map($tagToId) ->unique();
24. accidental accumulators
25. $points = 0; foreach($this->users as $user) { $points += $user->getPoints(); } return $points;
26. $points = 0; foreach($this->users as $user) { $points += $user->getPoints(); } return $points;
27. $addPoints = function(int $state, User $user): int { return $state + $user->getPoints(); }; return array_reduce($this->users, $addPoints, 0);
28. $addPoints = function(int $state, User $user): int { return $state + $user->getPoints(); }; return $this->users ->reduce($addPoints, 0);
29. combined
30. $isEnabled = function(User $u): bool { return !$u->isDisabled(); }; $isVisible = function(User $user): bool { return !$u->isHidden(); }; $userToPoints = function(User $user): int { return $user->getPoints(); }; $addPoints = function(int $st, User $u): int { return $st + $u->getPoints(); }; return $this->users ->filter($isEnabled) ->filter($isVisible) ->map($userToPoints) ->reduce($addPoints, 0);
31. $isEnabled = function(User $u): bool { return !$u->isDisabled(); }; $isVisible = function(User $user): bool { return !$u->isHidden(); }; $userToPoints = function(User $user): int { return $user->getPoints(); }; $addPoints = function(int $st, User $u): int { return $st + $u->getPoints(); }; return $this->users ->filter($isEnabled) ->filter($isVisible) ->map($userToPoints) ->reduce($addPoints, 0);
32. level 2: components
33. request lifecycle
34. entry | input → request routing | request → route controller | controller → response events | request → request | response → response forms | data → mapping validation | data → violations
35. $response = controller(route($request));
36. object graph serialization
37. objects → normalization → formatting → data data → parsing → hydration → objects
38. $json = format(normalize($user)) $user = hydrate(parse($json))
39. $normalizers = new NormalizerContainer(); $normalizers->add(User::class, function(User $u) { return [ 'id' => $u->getId(), 'email' => $u->getEmail(), ]; });
40. $hydrators = new HydratorContainer(); $hydrators->add(User::class, function(array $data) { return new User($data['id'], $data['email']); });
41. $formats = new FormatContainer(); $formats->add('json', new JsonFormat());
42. $s = new Serializard($normalizers, $hydrators, $formats); $user = new User(1337, 'email@example.com'); $json = $s->serialize($user, 'json'); $user = $s->unserialize($json, 'json', User::class);
43. shortcode processing
44. This is a [b]bold text[/b]. This is a <strong>bold text</strong>.
45. string → parse → process → replace → string
46. $string = replace(process(parse($input)))
47. $handlers = new HandlerContainer(); $handlers->add('b', function(ShortcodeInterface $s) { return '<strong>'.$s->getContent().'</strong>'; });
48. $parser = new RegexParser(); $parser = new WordpressParser(); $parser = new RegularParser();
49. $processor = new Processor($parser, $handlers); $text = 'This is a [b]bold text[/b].'; $result = $processor->process($text);
50. level 3: systems
51. modelling data flow
52. applications microservices APIs
53. challenges
54. purpose
55. comfort zone
56. "real world"
57. performance
58. summary
59. Slides: https://speakerdeck.com/thunderer/functional-approach-in-software-design Resources: https://github.com/thunderer/Shortcode https://github.com/thunderer/Serializard https://en.wikipedia.org/wiki/Functional_programming http://www.phptherightway.com/pages/Functional-Programming.html https://www.smashingmagazine.com/2014/07/dont-be-scared-of-functional-programming https://pragprog.com/magazines/2012-08/functional-thinking-for-the-imperative-mind http://lambdaconf.us/downloads/documents/lambdaconf_slfp.pdf Images: https://www.flickr.com/photos/kinematic/4078206226 (rocks) https://www.flickr.com/photos/kyetis/12506278675 (stones) https://www.flickr.com/photos/skyseeker/14404947216 (lightning)
60. questions?
61. how can I help? github /thunderer twitter @tmmx
62. please rate the talk and leave feedback joind.in/talk/c0b77
63. thanks! github /thunderer twitter @tmmx