Learn You a Functional JavaScript for Great Good

Learn You a Functional JavaScript for Great Good! Mike Harris

Functions! Closures! Currying! Combinators! Multimethods

> require("underscore");! { [Function]! _: [Circular],! VERSION: '1.6.0',! …! map: [Function],! …! filter: [Function],! reject: [Function],! …! compose: [Function],! after: [Function],! …! }

> require("allong.es");! { es: ! {! …! flip: [Function: unary],! …! curry: [Function: unary],! map: [Function: binary],! mapWith: [Function: binary],! mapArgumentsWith: [Function: binary],! filter: [Function: binary],! filterWith: [Function: binary],! …! allong: [Circular] }

> require("bilby");! {! …! curry: [Function: curry],! flip: [Function: flip],! identity: [Function: identity],! constant: [Function: constant],! compose: [Function: compose],! …! lens: [Function: lens],! isLens: [Function],! objectLens: [Function: objectLens],! …! }

nothing function nothing(){};! ! nothing();! undefined

ﬁve function five(){return 5;};! ! five();! 5

make  Five function makeFive(){! return function(){return 5;}! };! ! makeFive();! [Function]! var five = makeFive();! five();! 5

fAdd function five(){return 5;};! ! function fAdd(f, g){! return f() + g();! };! ! fAdd(five, five);! 10

function helloMaker(){! var greet = "Hello";! return function(){return greet;};! };! ! var hello = helloMaker();! hello();! ! 'Hello'

function helloMaker(){! var greet = "Hello";! return function(){return greet;};! };! ! var hello = helloMaker();! hello();! ! 'Hello' environment function

function counter(){! var count = 0;! return function(){return ++count;};! };! ! var ids = counter();! ! ids();! 1! ! ids();! 2

function counter(){! var count = 0;! return function(){return ++count;};! };! ! var ids = counter();! ! ids();! 1! ! ids();! 2 environment function

f(a, b, c, d) g(b, c, d) h(c, d) j(d)

f(a, b, c, d) Curry g(b, c, d) Curry h(c, d)Curry j(d)

ownAdd f(a, b, c) Curry g(b, c)Curry h(c)

var ownAdd = function(a){! return function(b){! return function(c){! return a + b + c;! }! }! };! ! ownAdd(1)(2)(3);! 6

var ownAdd = function(a){! return function(b){! return function(c){! return a + b + c;! }! }! };! ! ownAdd(1)(2)(3);! 6 ownAdd

var ownAdd = function(a){! return function(b){! return function(c){! return a + b + c;! }! }! };! ! var add1 = ownAdd(1);! add1(2)(3);! 6

var ownAdd = function(a){! return function(b){! return function(c){! return a + b + c;! }! }! };! ! var add1 = ownAdd(1);! add1(2)(3);! 6 add1 a = 1

var ownAdd = function(a){! return function(b){! return function(c){! return a + b + c;! }! }! };! ! var add3 = ownAdd(1)(2);! add3(3);! 6

var ownAdd = function(a){! return function(b){! return function(c){! return a + b + c;! }! }! };! ! var add3 = ownAdd(1)(2);! add3(3);! 6 add3 a = 1 b = 2

Combinators Moses Schönfinkel  and  Haskell Curry

Compose Function Function Function

var compose = require(“underscore").compose;! ! var sqAnd1 = compose(! function(x){return x+1;},! function(x){return x*x;}! );! ! sqAnd1(2);! 5

var! _ = require("underscore"),! compose = _.compose;

_.compose = function() {! var funcs = arguments;! return function() {! var args = arguments;! for (var i = funcs.length - 1; i >= 0; i--) {! args = [funcs[i].apply(this, args)];! }! return args[0];! };! };

var flip = require("bilby").flip;! ! function cat(s, t){return s + t;};! ! cat("Hello ", "Mike ");! 'Hello Mike '! ! flip(cat)("Hello ")("Mike ");! 'Mike Hello '

var flip = require("bilby").flip;! ! function cat(s, t){return s + t;};! ! var post = flip(cat);! ! var messageToMike = post("Mike ");! ! messageToMike("Hello ");! 'Hello Mike '! ! messageToMike("Bye ");! 'Bye Mike '

var! bilby = require("bilby"),! ﬂip = bilby.ﬂip;

function ﬂip(f) {! return function(a) {! return function(b) {! return f(b, a);! };! };! }

Filter _.filter = _.select = function(obj, predicate, context) { var results = []; if (obj == null) return results; if (nativeFilter && obj.filter === nativeFilter) return obj.filter(predicate, context); each(obj, function(value, index, list) { if (predicate.call(context, value, index, list)) results.push(value); }); return results; };

var filter = require("underscore").filter;! ! function isEven(x){return x%2 === 0;};! isEven(2);! true! ! filter([1, 2, 3], isEven);! [ 2 ]! ! [1, 2, 3].filter(isEven);! [ 2 ]

var! _ = require("underscore"),! ﬁlter = _.ﬁlter;

_.filter = _.select = function(obj, predicate, context) {! var results = [];! if (obj == null) return results;! if (nativeFilter && obj.filter === nativeFilter) ! return obj.filter(predicate, context);! each(obj, function(value, index, list) {! if (predicate.call(context, value, index, list))! results.push(value);! });! return results;! };

FilterWith var filter = binary( function filter (list, fn) { fn = functionalize(fn); return __filter.call(list, fn); }); var filterWith = flip(filter);

var filterWith = require("allong.es").allong.es.filterWith;! ! function isEven(x){return x%2 === 0;};! var evenOnly = filterWith(isEven);! ! evenOnly([1, 2, 3]);! [ 2 ]! ! evenOnly([42, 113]);! [ 42 ]! ! evenOnly([2, 1232, 131, 2, 13]);! [ 2, 1232, 2 ]

var! allonges = require("allong.es").allong.es,! ﬁlterWith = allonges.ﬁlterWith

var filter = binary( function filter (list, fn) {! fn = functionalize(fn);! ! return __filter.call(list, fn);! });! ! var filterWith = flip(filter);

Environment Method Predicate FunctionName

Environment Method Predicate FunctionName (name, predicate) name predicate function

var! bilby = require("bilby"),! environment = bilby.environment;

Animals voice cat meowspeak (speak, cat) speak cat meow

var animals = animals.method(! “speak",! isA(“cat"),! say("meow"));! var animals = animals.method(! “speak",! isA(“dog"),! say("woof"));! ! animals.speak({type: "dog"});! The dog says woof! ! animals.speak({type: "cat"});! The cat says meow

var animals = animals.method(! “speak",! isA(“cat"),! say("meow"));! var animals = animals.method(! “speak",! isA(“dog"),! say("woof"));! ! animals.speak({type: "dog"});! The dog says woof! ! animals.speak({type: "cat"});! The cat says meow name predicate function environment

var animals = animals.method(! "speak",! isA("fox"),! say(“Wa-pa-pa-pa-pa-pa-pow!")! );! ! animals.speak({type:"fox"});! The fox says Wa-pa-pa-pa-pa-pa-pow!

Dante, The Divine Comedy  Canto 24 A longer ladder yet remains to scale.

Functional JavaScript Michael Fogus

JavaScript Allonge Reginald Braithwaite

Learn You a Haskell for Great Good! Miran Lipovača

The Joy of Clojure Michael Fogus$ Chris Houser

Nietzsche, Human, All Too Human  Aphorism 633 Now we will no longer concede so easily that anyone has the truth.

Mike Harris  @MikeMKH! http://comp-phil.blogspot.com/

Learn You a Functional JavaScript for Great Good

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