PHP = PHunctional Programming
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The document presents an overview of functional programming (FP) in PHP, covering key concepts such as pure functions, higher-order functions, immutability, and function composition. It compares FP with object-oriented programming (OO) and introduces advanced topics like currying, functors, and monads, emphasizing the benefits of FP in achieving clear and predictable code. Additionally, the document provides resources for further exploration of functional programming in PHP and other languages.
PHP = PHunctional Programming
- 1. By Luis Atencio (@luijar) PHP = PHunctional Programming Northeast PHP Conference 2016
- 3. You don’t need to understand Category Theory to grok FP
- 4. Agenda 1. Understand the FP stuff 2. Function composition and declarative coding 3. Currying 4. Functors 5. Monads 6. Cool FP libs for PHP
- 6. PHP functions became instances of Closure
- 7. Mathematical-like computing ƛx.x + 1 The birth of the anonymous function! (ƛx.x + 1)3 = 4 (ƛx.x + 1)((ƛy.y + 2))3 = 6
- 8. What did we learn from the Maths? Pure Functions • No side effects! • Clear contracts input and output • Self-documenting • Stateless Immutability • Can’t change the contents of something once it’s been initialized Higher-order functions • Pass functions into other functions • Return functions from other functions
- 9. What is a side effect? A function execution that impacts its outer scope. The effect is more detrimental when it’s the global scope
- 10. Pure Functions A function without side effects that returns the same result on same input
- 11. Immutability • Look at immutability through the consistent (repeatable) execution of pure functions • Most bugs originate from data issues • Functions are (represent) immutable values • Very limited support in PHP
- 12. Higher-order functions • Pass functions to other functions • Return functions from other functions • Lazy evaluation
- 13. Variable functions • If a variable has parenthesis appended to it, PHP will try to invoke it • Can be passed in by name (string) or reference • Will not work with language constructs: • echo • print • unset • isset • empty
- 15. Composition vs Inheritance2 Adding new behavior is easy
- 16. Functions are first-class in PHP The Closure class was added in PHP 5.3.0
- 17. Everything is an object under the hood Syntactic Sugar
- 18. Towards more functional code PHP 4.0.6 introduced (but they are not pure!) to eliminate looping! • array_map() • array_filter() • array_reduce()
- 19. Application State: OO In OO you move state by passing objects around and invoking methods on those objects. In FP you pass state to the functions and combine them to move/transform it. ObjectA ObjectC ObjectB ObjectD
- 20. Application State: FP In FP you pass state to the functions and combine them to move/transform it. FuncA FuncC FuncB FuncD
- 21. FP vs OO Declarative vs Imperative Functions vs Objects Stateless vs Stateful Mutable vs Immutable
- 22. Declarative • Describe WHAT a program does • Not HOW to do it Unix pipeline SQL
- 23. Declarative2 Using PRamda Functional PHP Library https://github.com/kapolos/pramda
- 24. Lambda Expressions Arrow functions RFC under discussion https://wiki.php.net/rfc/arrow_functions
- 25. Function composition Declarative style + modularity
- 26. Function composition The composition of functions f and g is another function that takes the result of g and pass it to f: f o g = f( g(x) ) f g Input: AOutput: C A -> BB -> C B
- 27. Function composition2 Examples: This is where the term “Composer” comes from
- 28. Function composition3 It’s just the inverse of PIPE! Point-free style!
- 29. Currying • Composition requires we use single argument functions • Partially evaluate a function as a sequence of steps providing one argument at a time • PHP uses eager function evaluation function f(a, b) { … } f a evaluating: returns: ( )
- 30. Currying2 Transforms a multi-argument function into several single-arity functions function f(a, b) { … } curry(f) = function (a, b) { return function (a) { return function (b) { ... } } } wait to be invoked
- 35. Containers are not new Generalization
- 36. Protecting access to data ?
- 37. Mapping a value to a container strtolower HELLO HELLO Map function hello wrap Container HELLO Lift This is known as a Functor!!
- 38. Option Type Intended for cases when you might want to return a value—like an object, or (optionally) not—like null. https://github.com/schmittjoh/php-option vs
- 39. Option Type2 What to do with nested types? Introducing flatMap() This is known as a Monad!!
- 41. The Observable type Treat any type of data (of any size) as a composable stream. Makes use of the Observer pattern
- 44. Conclusion PHP = FP + OO “..FP in the small... OO in the large...” - Michael Feathers
- 45. Resources
- 46. Functional PHP Resource https://leanpub.com/functional-php Free to read!!!
- 47. Functional Programming in JavaScript Resource https://www.manning.com/atencio Get on Amazon
- 48. RxJS in Action Resource https://www.manning.com/books /rxjs-in-action Get on Manning.com
- 49. @luijar
Editor's Notes
- #3: Didn’t we just become fully OO with 5.3? Functional Programming is the extensive use of functions to move the application from one state to the next
- #5: Objective: Understand PHP bettter
- #7: This gives rise to HO functions. Since objects can be passed around and returned
- #8: Everything can be represented in the context of lambda expressions In school, we’re taught about Turing machines and Von Neumann Model
- #10: Pure functions: count. Exceptions are thrown, printing to the console Is time() a pure function?
- #11: Pure functions: count. Is time() a pure function?
- #12: const cannot be used to conditionally define constants. To define a global constant, it has to be used in the outermost scope: if (...) { const FOO = 'BAR'; // invalid } // but if (...) { define('FOO', 'BAR'); // valid } const accepts a static scalar (number, string or other constant like true, false, null, __FILE__), whereas define() takes any expression. Since PHP 5.6 constant expressions are allowed in const as well: const BIT_5 = 1 << 5; // valid since PHP 5.6, invalid previously define('BIT_5', 1 << 5); // always valid const takes a plain constant name, whereas define() accepts any expression as name. This allows to do things like this: for ($i = 0; $i < 32; ++$i) { define('BIT_' . $i, 1 << $i); } consts are always case sensitive, whereas define() allows you to define case insensitive constants by passing true as the third argument const simply reads nicer. It's a language construct instead of a function and also is consistent with how you define constants in classes. const defines a constant in the current namespace, while define() has to be passed the full namespace name: namespace A\B\C; // To define the constant A\B\C\FOO: const FOO = 'BAR'; define('A\B\C\FOO', 'BAR'); Since PHP 5.6 const constants can also be arrays, while define() does not support arrays yet. However arrays will be supported for both cases in PHP 7. const FOO = [1, 2, 3]; // valid in PHP 5.6 define('FOO', [1, 2, 3]); // invalid in PHP 5.6, valid in PHP 7.0 As consts are language constructs and defined at compile time they are a bit faster than define()s.
- #15: Adding a new strategy involves creating a new class. Ex. safeDivide
- #16: FP makes patterns disappear
- #19: No consistent API Cumbersome and verbose to use No currying Not immutable! They separate the loop away from your business logic
- #22: This gives rise to HO functions. Since objects can be passed around and returned
- #23: How to do it we let the compiler worry abo Variable functions ¶ PHP supports the concept of variable functions. This means that if a variable name has parentheses appended to it, PHP will look for a function with the same name as whatever the variable evaluates to, and will attempt to execute it. Among other things, this can be used to implement callbacks, function tables, and so forth. Variable functions won't work with language constructs such as echo, print, unset(), isset(), empty(), include,require and the like. Utilize wrapper functions to make use of any of these constructs as variable functions.
- #24: How to do it we let the compiler worry abo Variable functions ¶ PHP supports the concept of variable functions. This means that if a variable name has parentheses appended to it, PHP will look for a function with the same name as whatever the variable evaluates to, and will attempt to execute it. Among other things, this can be used to implement callbacks, function tables, and so forth. Variable functions won't work with language constructs such as echo, print, unset(), isset(), empty(), include,require and the like. Utilize wrapper functions to make use of any of these constructs as variable functions.
- #25: How to do it we let the compiler worry abo Variable functions ¶ PHP supports the concept of variable functions. This means that if a variable name has parentheses appended to it, PHP will look for a function with the same name as whatever the variable evaluates to, and will attempt to execute it. Among other things, this can be used to implement callbacks, function tables, and so forth. Variable functions won't work with language constructs such as echo, print, unset(), isset(), empty(), include,require and the like. Utilize wrapper functions to make use of any of these constructs as variable functions.
- #26: This gives rise to HO functions. Since objects can be passed around and returned
- #29: This is also known as point-free style
- #30: We can do this thanks to HO functions
- #34: This gives rise to HO functions. Since objects can be passed around and returned
- #37: Most errors are due to error in the data
- #38: This is a functor
- #39: You are documenting the fact that you’re using this type Option is a monad!
- #40: You are documenting the fact that you’re using this type Option is a monad!
- #41: Didn’t we just become fully OO with 5.3?
- #46: Didn’t we just become fully OO with 5.3? Functional Programming is the extensive use of functions to move the application from one state to the next