Christian Gill ''Functional programming for the people''
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The document discusses functional programming concepts including pure functions, higher-order functions, composition, and currying. It provides code examples to demonstrate these concepts, such as implementing functions to add numbers, compose functions, and curry functions to partially apply arguments. The document emphasizes that functional code should be predictable, testable, and avoid side effects by favoring pure functions over mutable data structures and methods with side effects.
![;[1, 2, 3].reduce((acc, i) => sum(acc, i), 0)
;[1, 2, 3].reduce(sum, 0)](https://image.slidesharecdn.com/christiangill-190823122557/85/Christian-Gill-Functional-programming-for-the-people-9-320.jpg)
![const calculations = [
(w) => w + w,
(x) => x + 1,
(y) => y / 2,
(z) => z * z * z,
]](https://image.slidesharecdn.com/christiangill-190823122557/85/Christian-Gill-Functional-programming-for-the-people-10-320.jpg)
![;[1, 2, 3].reduce(sum, 0)
const mult = (a) => (b) => a * b
const by2 = mult(2)
typeof by2 // 'function'
by2(2) // 4
mult(2)(2) // 4](https://image.slidesharecdn.com/christiangill-190823122557/85/Christian-Gill-Functional-programming-for-the-people-13-320.jpg)
![const xs = [1, 2, 3, 4, 5]
xs.splice(0, 3) // [1, 2, 3]
xs.splice(0, 3) // [4, 5]
xs.splice(0, 3) // []
xs // []](https://image.slidesharecdn.com/christiangill-190823122557/85/Christian-Gill-Functional-programming-for-the-people-20-320.jpg)
![const xs = [1, 2, 3, 4, 5]
xs.slice(0, 3) // [1, 2, 3]
xs.slice(0, 3) // [1, 2, 3]
xs.slice(0, 3) // [1, 2, 3]
xs // [1, 2, 3, 4, 5]](https://image.slidesharecdn.com/christiangill-190823122557/85/Christian-Gill-Functional-programming-for-the-people-21-320.jpg)
![// saveUser :: Db -> User -> Promise User
const saveUser = (Db) => Db.save
// production
const db = connect(config)
const saveUserToDB = saveUser(db)
// testing
const testDB = createTestDB({users: []})
const saveUserTest = saveUser(testsDB)](https://image.slidesharecdn.com/christiangill-190823122557/85/Christian-Gill-Functional-programming-for-the-people-29-320.jpg)
![const createTestDB = (obj) => ({
save: (user) => {
obj.users.push(user)
return Promise.resolve(obj.users)
},
})
saveUserTest('Carla') //=> Promise(['Carla'])
saveUserTest('Manu') //=> Promise(['Carla', 'Manu'])](https://image.slidesharecdn.com/christiangill-190823122557/85/Christian-Gill-Functional-programming-for-the-people-30-320.jpg)
![// live codign - implement compose
// (f ∘ g)(x) = f(g(x))
const compose = () => {}
const head = (xs) => xs[0]
const reverse = (xs) => [...xs].reverse()
const tail = (xs) => head(reverse(xs))
const arr = ['Odessa', 'JS', 'Rocks']
tail(arr)](https://image.slidesharecdn.com/christiangill-190823122557/85/Christian-Gill-Functional-programming-for-the-people-39-320.jpg)
![live coding - implement compose3
onst compose = (f, g) => (x) => f(g(x))
onst join = (delim) => (xs) => xs.join(delim)
onst toUpper = (str) => str.toUpperCase()
onst exclaim = (str) => str + '!!!'
onst titlelize = (xs) => exclaim(toUpper(join(' ')(xs)
onst arr = ['Odessa', 'JS', 'Rocks']
tlelize(arr)](https://image.slidesharecdn.com/christiangill-190823122557/85/Christian-Gill-Functional-programming-for-the-people-40-320.jpg)
![/ live coding - implement generic compose
onst compose = (f, g) => (x) => f(g(x))
onst compose3 = (f, g, h) => (x) => f(g(h(x)))
onst join = (delim) => (xs) => xs.join(delim)
onst toUpper = (str) => str.toUpperCase()
onst exclaim = (str) => str + '!!!'
onst h1 = (str) => '<h1>' + str + '</h1>'
onst titlelize = compose3(exclaim, toUpper, join(' ')
onst arr = ['Odessa', 'JS', 'Rocks']
itlelize(arr)](https://image.slidesharecdn.com/christiangill-190823122557/85/Christian-Gill-Functional-programming-for-the-people-41-320.jpg)
Christian Gill ''Functional programming for the people''
- 1. Functional Programming for the People
- 3. A monad in X is just a monoid in the category of endofunctors of X. Saunders Mac Lane. Categories for the Working Mathematician
- 5. What does it mean to write functional code?
- 6. code terse, yet easy to reason about don't reinvent the wheel represent problems in terms of generic, composable bits benefit from laws
- 7. First class citizens (functions are values)
- 8. const add = (a, b) => a + b const sum = (x, y) => add(x, y) sum(1, 2) // 3 const sum = add sum(1, 2) // 3
- 9. ;[1, 2, 3].reduce((acc, i) => sum(acc, i), 0) ;[1, 2, 3].reduce(sum, 0)
- 10. const calculations = [ (w) => w + w, (x) => x + 1, (y) => y / 2, (z) => z * z * z, ]
- 11. const obj = { f: (x) => x + 1, g: (y) => y / 2, h: (z) => z * z * z, }
- 13. ;[1, 2, 3].reduce(sum, 0) const mult = (a) => (b) => a * b const by2 = mult(2) typeof by2 // 'function' by2(2) // 4 mult(2)(2) // 4
- 14. const fs = require('fs') fs.readFile('file.txt', (err, text) => { if (err) { console.error('Error:', err) return } console.log('File content: ', text) })
- 15. fetch(url) .then((res) => res.json()) .then(({data}) => console.log(data))
- 16. Pure functions
- 17. A pure function is a function that, given the same input, will always return the same output and does not have any observable side effect. Brian Lonsdorf Mostly adequate guide to FP
- 18. Math.random() // 0.08140343648722337 Date.now() // 1560981656763
- 19. splice vs. slice
- 20. const xs = [1, 2, 3, 4, 5] xs.splice(0, 3) // [1, 2, 3] xs.splice(0, 3) // [4, 5] xs.splice(0, 3) // [] xs // []
- 21. const xs = [1, 2, 3, 4, 5] xs.slice(0, 3) // [1, 2, 3] xs.slice(0, 3) // [1, 2, 3] xs.slice(0, 3) // [1, 2, 3] xs // [1, 2, 3, 4, 5]
- 22. Predictability
- 23. But what if I want to (write a file|save to databse|fetch from server) ?!
- 25. pure functions === easy tests
- 26. same input -> same output
- 27. no observable side effects
- 28. const saveUser = (user) => Db.save(user) const saveUser = (Db) => (user) => Db.save(user) const saveUser = (Db) => Db.save
- 29. // saveUser :: Db -> User -> Promise User const saveUser = (Db) => Db.save // production const db = connect(config) const saveUserToDB = saveUser(db) // testing const testDB = createTestDB({users: []}) const saveUserTest = saveUser(testsDB)
- 30. const createTestDB = (obj) => ({ save: (user) => { obj.users.push(user) return Promise.resolve(obj.users) }, }) saveUserTest('Carla') //=> Promise(['Carla']) saveUserTest('Manu') //=> Promise(['Carla', 'Manu'])
- 33. Redux f(state, action) -> state
- 34. const add = (a) => (b) => a + b const inc = add(1) // =) inc(1) // 2 add(1)(3) // 4 =(
- 35. const add = (a, b) => a + b const inc = (b) => add(1, b) // =( inc(1) // 2 add(1, 3) // 4 =)
- 36. Currying & Partial Application
- 37. // live coding - implement curry const add = (a) => (b) => a + b const inc = add(1) inc(10) add(10)(20)
- 38. Composition (f ∘ g)(x) = f(g(x))
- 39. // live codign - implement compose // (f ∘ g)(x) = f(g(x)) const compose = () => {} const head = (xs) => xs[0] const reverse = (xs) => [...xs].reverse() const tail = (xs) => head(reverse(xs)) const arr = ['Odessa', 'JS', 'Rocks'] tail(arr)
- 40. live coding - implement compose3 onst compose = (f, g) => (x) => f(g(x)) onst join = (delim) => (xs) => xs.join(delim) onst toUpper = (str) => str.toUpperCase() onst exclaim = (str) => str + '!!!' onst titlelize = (xs) => exclaim(toUpper(join(' ')(xs) onst arr = ['Odessa', 'JS', 'Rocks'] tlelize(arr)
- 41. / live coding - implement generic compose onst compose = (f, g) => (x) => f(g(x)) onst compose3 = (f, g, h) => (x) => f(g(h(x))) onst join = (delim) => (xs) => xs.join(delim) onst toUpper = (str) => str.toUpperCase() onst exclaim = (str) => str + '!!!' onst h1 = (str) => '<h1>' + str + '</h1>' onst titlelize = compose3(exclaim, toUpper, join(' ') onst arr = ['Odessa', 'JS', 'Rocks'] itlelize(arr)
- 42. Composition is fractal operation -> service -> use case -> app
- 43. { coding time -- small CLI example app }
- 44. What does it mean to write functional code?
- 47. Thλnks!