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Building Functional Islands
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Mark Jones
April 28, 2016
Technology
2
600
Building Functional Islands
A talk about functional programming at the April 2016 Front End London
http://frontendlondon.co.uk
Mark Jones
April 28, 2016
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Transcript
Building Functional Islands
Audience Participation
What is Functional Programming?
Statements const nums = [1, 2, 3]; const doubled =
[]; for (let i = 0; i < nums.length; i++) { doubled.push(nums[i] * 2); }
Statements const nums = [1, 2, 3]; const doubled =
[]; for (let i = 0; i < nums.length; i++) { doubled.push(nums[i] * 2); }
Statements const nums = [1, 2, 3]; const doubled =
[]; for (let i = 0; i < nums.length; i++) { doubled.push(nums[i] * 2); }
Statements const nums = [1, 2, 3]; const doubled =
[]; for (let i = 0; i < nums.length; i++) { doubled.push(nums[i] * 2); }
function double(x) { return x * 2; } map([1, 2,
3], double); Expressions
function double(x) { return x * 2; } map([1, 2,
3], double); // [(1 * 2), (2 * 2), (3 * 2)] Expressions
function double(x) { return x * 2; } map([1, 2,
3], double); // [(1 * 2), (2 * 2), (3 * 2)] // [2, 4, 6] Expressions
Why Functional Programming?
Functions Island Building Block #1
First-Class Functions function onClick() { // I'm a first-class function
} document.body.addEventListener('click', onClick);
function onClick() { // I get called by a higher-order
function } document.body.addEventListener('click', onClick); Higher-Order Functions
Higher-Order Functions function logify(fn) { return (...args) => { console.log(args);
return fn(...args); }; } const logifyAdd = logify(add); function add(x, y) { return x + y; }
Higher-Order Functions function logify(fn) { return (...args) => { console.log(args);
return fn(...args); }; } const logifyAdd = logify(add); function add(x, y) { return x + y; }
Higher-Order Functions function logify(fn) { return (...args) => { console.log(args);
return fn(...args); }; } const logifyAdd = logify(add); function add(x, y) { return x + y; }
Higher-Order Functions const logifyAdd = logify(add); logifyAdd(1, 2); // [1,
2] // 3
Higher-Order Functions The Benefits
Pure Functions function add(x, y) { // I'm a pure
function return x + y; }
Pure Functions add(1, 2) + add(3, 4);
Pure Functions add(1, 2) + add(3, 4); // 3 +
add(3, 4);
Pure Functions add(1, 2) + add(3, 4); // 3 +
add(3, 4); // 3 + 7;
Pure Functions add(1, 2) + add(3, 4); // 3 +
add(3, 4); // 3 + 7; // 10;
function addAndSomethingElse(x, y) { // I'm an impure function doSomethingElse();
return x + y; } Pure Functions
Pure Functions addAndSomethingElse(1, 2) // ???
Pure Functions The Benefits
Pure Functions The Reality
Immutability Island Building Block #2
Immutable values const nums = [1, 2, 3]; const person
= { name: 'mark', age: 29 }; nums[0] = 2; // [2, 2, 3] person.age = 27; // { name: 'mark', age: 27 }
Immutable values const nums = [1, 2, 3]; const person
= { name: 'mark', age: 29 }; nums[0] = 2; // [2, 2, 3] person.age = 27; // { name: 'mark', age: 27 }
Immutable values const nums = [1, 2, 3]; const person
= { name: 'mark', age: 29 }; nums[0] = 2; // [2, 2, 3] person.age = 27; // { name: 'mark', age: 27 }
Immutable values const nums = [1, 2, 3]; const person
= { name: 'mark', age: 29 }; nums[0] = 2; // [2, 2, 3] person.age = 27; // { name: 'mark', age: 27 }
Object.freeze const nums = Object.freeze([1, 2, 3]); const person =
Object.freeze({ name: 'mark', age: 29 }); nums[0] = 2; // [1, 2, 3] person.age = 27; // { name: 'mark', age: 29 }
Object.freeze const nums = Object.freeze([1, 2, 3]); const person =
Object.freeze({ name: 'mark', age: 29 }); nums[0] = 2; // [1, 2, 3] person.age = 27; // { name: 'mark', age: 29 }
Object.freeze const nums = Object.freeze([1, 2, 3]); const person =
Object.freeze({ name: 'mark', age: 29 }); nums[0] = 2; // [1, 2, 3] person.age = 27; // { name: 'mark', age: 29 }
Object.freeze const employee = Object.freeze({ department: 'Eng', profile: { name:
'mark', age: 29 } }); employee.profile.age = 27; // {...{ name: 'mark', age: 27 } }
Object.freeze const employee = Object.freeze({ department: 'Eng', profile: { name:
'mark', age: 29 } }); employee.profile.age = 27; // {...{ name: 'mark', age: 27 } }
Object.freeze const employee = Object.freeze({ department: 'Eng', profile: { name:
'mark', age: 29 } }); employee.profile.age = 27; // {...{ name: 'mark', age: 27 } }
deepFreeze const employee = deepFreeze({ department: 'Eng', profile: { name:
'mark', age: 29 } }); employee.profile.age = 27; // {...{ name: 'mark', age: 29 } }
Immutability The Benefits
Immutability The Reality
Currying Island Building Block #3
Currying const add = curry((x, y) => { return x
+ y; }); const succ = add(1); succ(1); // 2
Currying const add = curry((x, y) => { return x
+ y; }); const succ = add(1); succ(1); // 2
Currying const add = curry((x, y) => { return x
+ y; }); const succ = add(1); succ(1); // 2
Currying const devs = [ { firstName: 'mark' }, {
firstName: 'sally' } ]; const firstNames = map(devs, (dev) => { return dev.firstName; });
Currying const devs = [ { firstName: 'mark' }, {
firstName: 'sally' } ]; const firstNames = map(devs, (dev) => { return dev.firstName; });
Currying const devs = [ { firstName: 'mark' }, {
firstName: 'sally' } ]; const firstNames = map(devs, (dev) => { return dev.firstName; });
Currying const devs = [ { firstName: 'mark' }, {
firstName: 'sally' } ]; const getFirstNames = map(prop('firstName')); const firstNames = getFirstNames(devs);
Currying const devs = [ { firstName: 'mark' }, {
firstName: 'sally' } ]; const getFirstNames = map(prop('firstName')); const firstNames = getFirstNames(devs);
Currying const devs = [ { firstName: 'mark' }, {
firstName: 'sally' } ]; const getFirstNames = map(prop('firstName')); const firstNames = getFirstNames(devs);
Currying const devs = [ { firstName: 'mark' }, {
firstName: 'sally' } ]; const getFirstNames = map(prop('firstName')); const firstNames = getFirstNames(devs);
Currying The Benefits
Currying The Reality
Composition Island Building Block #4
Composition const value = 1; const gRes = g(value); const
fgRes = f(gRes);
Composition const value = 1; const gRes = g(value); const
fgRes = f(gRes);
Composition const value = 1; const gRes = g(value); const
fgRes = f(gRes);
Composition const value = 1; const gRes = g(value); const
fgRes = f(gRes);
Composition function fg(x) { return f(g(x)); } fg(1);
Composition const fg = compose(f, g); fg(1);
Composition function getFilmIdsFromResponse(resp) { return getIds(getFilms(JSON.parse(resp))); } getFilmIdsFromResponse('{ "films": [{
id: 1 }, ...], "actors": [...] }');
Composition function getFilmIdsFromResponse(resp) { return getIds(getFilms(JSON.parse(resp))); } getFilmIdsFromResponse('{ "films": [{
id: 1 }, ...], "actors": [...] }');
Composition function getFilmIdsFromResponse(resp) { return getIds(getFilms(JSON.parse(resp))); } getFilmIdsFromResponse('{ "films": [{
id: 1 }, ...], "actors": [...] }');
Composition function getFilmIdsFromResponse(resp) { return getIds(getFilms(JSON.parse(resp))); } getFilmIdsFromResponse('{ "films": [{
id: 1 }, ...], "actors": [...] }');
Composition function getFilmIdsFromResponse(resp) { return getIds(getFilms(JSON.parse(resp))); } getFilmIdsFromResponse('{ "films": [{
id: 1 }, ...], "actors": [...] }');
Composition const getIds = map(prop('id')); const getFilmIdsFromResponse = compose(getIds, prop('films'),
JSON.parse); getFilmIdsFromResponse('{ "films": [...], "actors": [...] }');
Composition const getIds = map(prop('id')); const getFilmIdsFromResponse = compose(getIds, prop('films'),
JSON.parse); getFilmIdsFromResponse('{ "films": [...], "actors": [...] }');
Composition const getIds = map(prop('id')); const getFilmIdsFromResponse = compose(getIds, prop('films'),
JSON.parse); getFilmIdsFromResponse('{ "films": [...], "actors": [...] }');
Composition const getIds = map(prop('id')); const getFilmIdsFromResponse = compose(getIds, prop('films'),
JSON.parse); getFilmIdsFromResponse('{ "films": [...], "actors": [...] }');
Composition const getIds = map(prop('id')); const getFilmIdsFromResponse = compose(getIds, prop('films'),
JSON.parse); getFilmIdsFromResponse('{ "films": [...], "actors": [...] }');
Composition The Benefits
Composition The Reality
I’m confused. What’s a functional island again?
Further reading / watch list (free) https://drboolean.gitbooks.io/mostly-adequate-guide/content/ Professor Frisby's Mostly
Adequate Guide to Functional Programming http://ramdajs.com/ A practical functional library for Javascript programmers https://github.com/lodash/lodash/wiki/FP-Guide lodash/fp guide https://www.youtube.com/watch?v=m3svKOdZijA Hey Underscore, You're Doing It Wrong! https://github.com/substack/deep-freeze deepFreeze
Further reading / watch list (paid) https://frontendmasters.com/courses/functional-js-lite/ Functional Lite JavaScript
https://frontendmasters.com/courses/functional-javascript/ Hardcore Functional Programming in JavaScript
Thank you. @mark_ jones