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crocks is a collection of popular Algebraic Data Types (ADTs) that are all the rage in functional programming. You have heard of things like Maybe and Either and heck maybe even IO, that is what these are. The main goal of crocks is to curate and provide not only a common interface between each type (where possible of course), but also provide all of the helper functions needed to hit the ground running.

Table of Contents


crocks is available from npm and is just a shell command away. All you need to do is run the following to save it as a dependency in your current project folder:

$ npm install crocks -S


There are many options to use crocks to suit the needs of your, projects. When used on the backend or in an environment where size is not a big concern, the entire lib can be brought in and the various elements can be either be plucked off of or referenced by the namespace.

For those cases where size matters, like in the case of frontend bundle building, the individual entities can be brought in. This will ensure that your finished bundles include only what is needed for your application/program.

For using the latter case, refer to the desired function's documentation to find the path in which it resides.

Entire crocks library (CommonJS)

// namespace entire suite to crocks variable
const crocks = require('crocks')

// pluck anything that does not require name-spacing
const { safe, isNumber } = crocks

// still requires entire object, but removes name-spacing
const { and, liftA2 } = require('crocks')

Entire crocks library (JS Modules)

// namespace entire suite to crocks variable
import crocks from 'crocks'

// still imports entire object, but removes name-spacing
import { and, liftA2 }  from 'crocks'

// pluck anything that does not require name-spacing
const { safe, isNumber } = crocks

Single entities (CommonJS)

// require in each entity directly
const and = require('crocks/logic/and')
const curry = require('crocks/helpers/curry')
const isNumber = require('crocks/predicates/isNumber')
const liftA2 = require('crocks/helpers/liftA2')
const safe = require('crocks/Maybe/safe')

Single entities (JS Modules)

// import in each entity directly
import and from 'crocks/logic/and'
import curry from 'crocks/helpers/curry'
import isNumber from 'crocks/predicates/isNumber'
import liftA2 from 'crocks/helpers/liftA2'
import safe from 'crocks/Maybe/safe'


Documentation references: and, curry, predicates (isNumber), liftA2, safe.

// divide :: Number -> Number -> Number
const divide = x => y =>
  x / y

// safeNumber :: a -> Maybe Number
const safeNumber =

// notZero :: a -> Maybe Number
const notZero = safe(
  and(isNumber, x => x !== 0)

// safeDivide:: a -> a -> Maybe Number
const safeDivide = curry(
  (x, y) => liftA2(divide, safeNumber(x), notZero(y))

//=> Nothing

safeDivide(20, 0)
//=> Nothing

safeDivide(20, 5)
//=> Just 4

safeDivide('number', 5)
//=> Nothing


What is Included?

There are (8) classifications of "things" included in this library:

  • Crocks: These are the ADTs that this library is centered around. They are all Functor based Data Types that provide different computational contexts for working in a more declarative, functional flow. For the most part, a majority of the other bits in crocks exist to serve these ADTs.

  • Monoids: These helpful ADTs are in a class of their own, not really Functors in their own right (although some can be), they are still very useful in our everyday programming needs. Ever need to sum a list of numbers or mix a mess of objects together? This is were you will find the ADTs you need to do that.

  • Combinators: A collection of functions that are used for working with other functions. These do things like compose (2) functions together, or flip arguments on a function. They typically either take a function, return a function or a bit a both. These are considered the glue that holds the mighty house of crocks together and a valuable aid in writing reusable code.

  • Helper Functions: All other support functions that are either convenient versions of combinators or not even combinators at all cover this group.

  • Logic Functions: A helpful collection of logic based functions. All of these functions work with either predicate functions or instances of Pred and let you combine them in some very interesting ways.

  • Predicate Functions: A helpful collection of predicate functions to get you started.

  • Point-free Functions: Wanna use these ADTs in a way that you never have to reference the actual data being worked on? Well here is where you will find all of these functions to do that. For every algebra available on both the Crocks and Monoids there is a function here.

  • Transformation Functions: All the functions found here are used to transform from one type to another, naturally. These come are handy in situations where you have functions that return one type (like an Either), but are working in a context of another (say Maybe). You would like to compose these, but in doing so will result in a nesting that you will need to account for for the rest of your flow.


Thanks goes to these wonderful people (emoji key):

Ian Hofmann-Hicks

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Andrew Van Slaars

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Henrique Limas

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Robert Pearce

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Scott McCormack


Fred Daoud


Karthik Iyengar

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Jon Whelan

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Benny Powers

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Dale Francis

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Dipen Bagia


Andrew Jones


W. K. Seymour III


Eliseu Benedito Codinhoto



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Michael Wolfenden


Johan Codinha


Matt Ross


Jasmina Jacquelina

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Denis Zolkin


Zhentian Wan



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Furkan TunalΔ±

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Paul Desmond Parker


Rodrigo Erades


Jamie Dixon


Basant Pandey



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Example dbagia


A collection of well known Algebraic Data Types for your utter enjoyment.

Crocks Info

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😎 Author evilsoft