ramda

What is ramda?

Ramda is a functional programming library for JavaScript that makes it easy to create functional pipelines, without mutating data. It emphasizes a purer functional style, with functions that are automatically curried and composed of small, reusable, and combinable functions.

What are ramda's main functionalities?

Immutability and Side-Effect Free Functions

Ramda functions do not mutate the input data and do not cause side effects, making it easier to reason about code.

const increment = R.map(R.add(1));
const result = increment([1, 2, 3]); // [2, 3, 4]

Function Composition

Ramda provides compose and pipe functions for combining functions into new functions, facilitating functional composition.

const getNames = R.compose(R.map(R.prop('name')), R.filter(R.propEq('isActive', true)));
const users = [{name: 'Alice', isActive: true}, {name: 'Bob', isActive: false}];
const activeUserNames = getNames(users); // ['Alice']

Automatic Currying

Ramda functions are automatically curried, allowing you to easily create new functions by partially applying arguments.

const addFourNumbers = (a, b, c, d) => a + b + c + d;
const curriedAddFourNumbers = R.curry(addFourNumbers);
const f = curriedAddFourNumbers(1, 2);
const g = f(3);
const result = g(4); // 10

Data Transformation

Ramda provides a suite of tools for transforming data structures, such as arrays and objects, in a declarative and functional way.

const sortByAge = R.sortBy(R.prop('age'));
const people = [{name: 'John', age: 23}, {name: 'Jane', age: 21}];
const sortedPeople = sortByAge(people); // [{name: 'Jane', age: 21}, {name: 'John', age: 23}]

Other packages similar to ramda

lodash

Lodash is a JavaScript utility library that offers similar functionality to Ramda, such as data manipulation and functional utilities. However, Lodash is not as strictly functional as Ramda and does not emphasize currying and function composition to the same extent.

underscore

Underscore.js is another utility library that provides functional programming helpers. It is similar to Lodash and predates both Lodash and Ramda. It has a more OOP-style approach and lacks the auto-currying and functional composition features that are core to Ramda.

immutable

Immutable.js provides persistent immutable data structures which can be used in a functional programming style. Unlike Ramda, which works with plain JavaScript types, Immutable.js uses its own types and provides different APIs for manipulating these structures.

fp-ts

fp-ts is a library for typed functional programming in TypeScript. It provides type-safe functional programming structures and utilities, and it is more focused on types and type-level programming compared to Ramda.

README

Project Ramda

A practical functional library for Javascript programmers.

Goals

Using this library should feel as much like using Javascript as possible. Of course it's functional Javascript, but we're not introducing lambda expressions in strings, we're not borrowing consed lists, we're not porting over all of the Clojure functions.

Our basic data structures will be normal Javascript objects, and our usual collections will be Javascript arrays. We will not try to reach the point where all the functions have only zero, one, or two arguments. We will certainly try to keep some of the normal features of Javascript that seem to be unusual in functional languages, including variable length function signatures and functions as objects with properties.

Ramda will never be a drop-in replacement for Underscore (or LoDash, or even a drop-in-and-mechanically-switch-the-parameter-order-everywhere replacement.) It is intended to work with a different style of coding. Functional programming is in good part about immutable objects and side-effect free functions. While Ramda does not expect to do anything to enforce that style, its code should always work to make that style as frictionless as possible.

As much as we can, we would like the implementation to be both clean and elegant. But the API is king: we will sacrifice a great deal of implementation elegance for even a slightly cleaner API.

Unlike the developers of that silly-named Eweda project, though, this one will focus also on performance, striving for a reliable and quick implementation over any notions of functional purity.

Installation

To use with node:

$ npm install ramda

Then in the console:

var ramda = require('ramda');

To use directly in the browser:

<script src="path/to/yourCopyOf/ramda.js"></script>

or the minified version:

<script src="path/to/yourCopyOf/ramda.min.js"></script>

or from a CDN, either cdnjs:

<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.8.0/ramda.min.js"></script>

or one of the below links from jsDelivr:

<script src="//cdn.jsdelivr.net/ramda/0.8.0/ramda.min.js"></script>
<script src="//cdn.jsdelivr.net/ramda/0.8/ramda.min.js"></script>
<script src="//cdn.jsdelivr.net/ramda/latest/ramda.min.js"></script>

(note that using latest is taking a significant risk that ramda API changes could break your code.)

These script tags add the variable ramda on the browser's global scope.

Or you can inject ramda into virtually any unsuspecting web site using this bookmarklet:

javascript:(function(){var el=document.createElement('div'),b=document.getElementsByTagName('body')[0];msg='';el.style.position='fixed';el.style.height='32px';el.style.width='220px';el.style.marginLeft='-110px';el.style.top='0';el.style.left='50%';el.style.padding='5px 10px';el.style.zIndex=1001;el.style.fontSize='12px';el.style.color='#222';el.style.backgroundColor='#f99';if(typeof ramda!='undefined'){msg='This page already using ramda v'+ramda.version;return showMsg()}function getScript(url,success){var script=document.createElement('script');script.src=url;var head=document.getElementsByTagName('head')[0],done=false;script.onload=script.onreadystatechange=function(){if(!done&&(!this.readyState||this.readyState=='loaded'||this.readyState=='complete')){done=true;success();script.onload=script.onreadystatechange=null;head.removeChild(script)}};head.appendChild(script)}getScript('http://cdn.jsdelivr.net/ramda/latest/ramda.min.js',function(){if(typeof ramda=='undefined'){msg='Sorry, but Ramda wasn\'t able to load'}else{msg='This page is now Ramda-fied with v'+ramda.version}return showMsg()});function showMsg(){el.innerHTML=msg;b.appendChild(el);window.setTimeout(function(){if(typeof jQuery=='undefined'){b.removeChild(el)}else{jQuery(el).fadeOut('slow',function(){jQuery(this).remove()})}},2500)}})();

Documentation

Please review the API documentation.

Introductions

• Introducing Ramda by Buzz de Cafe
• Why Ramda? by Scott Sauyet
• Favoring Curry by Scott Sauyet

The Name

Ok, so we like sheep. That's all. It's a short name, not already taken. It could as easily have been eweda, but then we would be forced to say eweda lamb!, and no one wants that. For non-English speakers, lambs are baby sheep, ewes are female sheep, and rams are male sheep. So perhaps ramda is a grown-up lambda... but probably not.

Structure

Automatic Currying

The functions included should automatically allow for partial application without an explicit call to lPartial. Many of these operate on lists. A single list parameter should probably come last, which might conflict with the design of other libraries that have strong functional components (I'm looking at you Underscore!)

The idea is that, if foldl has this signature:

var foldl = function(fn, accum, arr) { /* ... */}

and we have this simple function:

var add = function(a, b) {return a + b;};

then, instead of having to manually call lPartial like this:

var sum = lPartial(foldl, add, 0);
var total = sum([1, 2, 3, 4]);

with ramda, we can just do this:

var sum = foldl(add, 0);
var total = sum([1, 2, 3, 4]);

Running The Test Suite

Console:

To run the test suite from the console, you need to have mocha installed:

npm install -g mocha

Then from the root of the project, you can just call

mocha

Alternately, if you've installed the dependencies, via:

npm install
npm install -g grunt-cli

then you can run the tests (and get more detailed output) via our grunt task:

grunt test

Browser:

To run the test suite in the browser, you can simply open test/index.html.

Alternatively, you can use testem to test across different browsers (or even headlessly), with livereloading of tests too. Install testem (npm install -g testem) and run testem. Open the link provided in your browser and you will see the results in your terminal.

If you have PhantomJS installed, you can run testem -l phantomjs to run the tests completely headlessly.

So What's With Eweda?

The eweda library was written by the developers of this library, with similar goals. But that one strove more for implementation elegance than for practical capabilities. Ramda is all about giving users real-world tools. Eweda can be seen more as an academic excercise, mostly proving out what does and doesn't work, and doing so as elegantly as possible.

Acknowledgements

Thanks to J. C. Phillipps for the Ramda logo. Ramda logo artwork © 2014 J. C. Phillipps. Licensed Creative Commons CC BY-NC-SA 3.0.