functional.js

functional.js (λ)

functional.js is a functional JavaScript library. It facilitates currying, point-free / tacit programming and monads.

Getting started

Using npm

npm install functional.js

To then include functional.min.js in your app:

var λ = require("functional.js");

Direct dependency

Download the minified version here, reference the js file and λ will become a global variable.

Using client side

There are possible issues with using the "λ" character client side. There shouldn't be, but there are. If you experience issues, there is an alternative client version, functional.min.client.js which uses "lambda" instead of "λ". Download the minified client version here, reference the js file and lambda will become a global variable.

Examples

Basic λ.curry example

var concatenate = λ.curry(function(word1, word2) {
    return word1 + " " + word2;
});

var concatenateHello = concatenate("Hello");
var result = concatenateHello("World");

expect(result).toEqual("Hello World");

Another λ.curry example

var add = λ.curry(function(arg1, arg2, arg3) {
    return arg1 + arg2 + arg3;
}); 

var add3 = add(3),
    add5 = add3(2);

expect(add(3)(2)(1)).toEqual(6);
expect(add3(2, 1)).toEqual(6);
expect(add3(2)(1)).toEqual(6);
expect(add5(1)).toEqual(6);

Extending arity with λ.curry example

var add = λ.curry(function(arg1, arg2) {
    return arg1 + arg2;
});

var add3 = add(3);

expect(add(1, 2, 3)).toEqual(6);
expect(add3(1, 2, 3, 4, 5)).toEqual(18);

Curried λ.each example

var result = [],
    items = ["f", "u", "n", "c"];

var addTo = function (item) {
    return result.push(item);
};

var addToResult = λ.each(addTo);
expect(typeof (addToResult)).toEqual("function");

addToResult(items);
expect(result).toEqual(["f", "u", "n", "c"]);

Curried λ.map example

var items = [1, 2, 3];

var doubleUp = function (number) {
    return number * 2;
};

var doubleMap = λ.map(doubleUp);
expect(typeof (doubleMap)).toEqual("function");

var result = doubleMap(items);
expect(result).toEqual([2, 4, 6]);

Curried λ.reduce example

var items = [1, 2, 3];

var multiply = function (arg1, arg2) {
    return arg1 * arg2;
};

var multiplyReduceFrom1 = λ.reduce(multiply, 1);
expect(typeof (multiplyReduceFrom1)).toEqual("function");

var result = multiplyReduceFrom1(items);
expect(result).toEqual(6);

Curried λ.any example

var items1 = [1, 2, 3],
    items2 = [1, 3, 5];

var even = function (item) {
    return item % 2 === 0;
};

var anyEven = λ.any(even);

expect(anyEven(items1)).toBeTruthy();
expect(anyEven(items2)).not.toBeTruthy();

Curried λ.select example

var items = [1, 2, 3, 4, 5];

var even = function (item) {
    return item % 2 === 0;
};
var odd = function (item) {
    return item % 2 !== 0;
};

var selectEven = λ.select(even);
var selectOdd = λ.select(odd);

expect(selectEven(items)).toEqual([2, 4]);
expect(selectOdd(items)).toEqual([1, 3, 5]);

Curried λ.first example

var items = [5, 4, 3, 2, 1];

var even = function (item) {
    return item % 2 === 0;
};
var odd = function (item) {
    return item % 2 !== 0;
};

var firstEven = λ.first(even);
var firstOdd = λ.first(odd);

expect(firstEven(items)).toEqual(2);
expect(firstOdd(items)).toEqual(1);

Curried λ.last example

var items = [5, 4, 3, 2, 1];

var even = function (item) {
    return item % 2 === 0;
};
var odd = function (item) {
    return item % 2 !== 0;
};

var lastEven = λ.last(even);
var lastOdd = λ.last(odd);

expect(lastEven(items)).toEqual(2);
expect(lastOdd(items)).toEqual(1);

Curried λ.every example

var items = [2, 4, 6, 8];

var even = function (item) {
    return item % 2 === 0;
};
var odd = function (item) {
    return item % 2 !== 0;
};

var everyEven = λ.every(even);
var everyOdd = λ.every(odd);

expect(everyEven(items)).toEqual(true);
expect(everyOdd(items)).toEqual(false);

Multiple λ.compose example

var e = function (a) {
    return "hello " + a;
};
var f = function (a) {
    return a + 1;
};
var g = function (a) {
    return a * 100;
};
var composed = λ.compose(e, f, g);

expect(composed(2)).toEqual("hello 201");

Curried λ.partition example

var items = [7, 6, 5, 4, 3, 2, 1];

var even = function (item) {
    return item % 2 === 0;
};

var partitionEven = λ.partition(even);

var result = partitionEven(items);

expect(result).toEqual([[6, 4, 2], [7, 5, 3, 1]]);

Monad λ.identity example

var val = 2;
expect(λ.identity(val)()).toEqual(val);

Monad λ.maybe example

var add = λ.curry(function(arg1, arg2) {
    return arg1 + arg2;
});

var maybeAdd2 = λ.maybe(add(2));

expect(maybeAdd2(null)).toEqual(null);
expect(maybeAdd2(undefined)).toEqual(undefined);
expect(maybeAdd2(3)).toEqual(5);