Koeus NPM | npm.io

Koeus

A small functional library for javascript

About

The K Combinator + Coeus (Greek Titan of Intellect) === Koeus. I found an alternative spelling of Coeus, spelled KOIOS and facepalmed. This is a small utility library that has little to no dependencies. If you need something greater, I suggest you reach for Ramda or if you've jumped into the deep end of the pool you could look at Folktale.

If you're still unsatisfied, you could look at Elm or for the purists, Purescript.

Installation

First:

npm install koeus

Example of usage:

Note: All non-unary functions that do not have a variable number of arguments (such as pipe) are auto curried, so that you can apply some or all arguments to it.

import { map } from 'koeus'

const xs = map(x => x + 1, [1,2,3]) // [2,3,4]

// or, because map is auto curried

const addOne = x => x + 1
const mapAddOne(addOne)
const ys = mapAddOne([1,2,3]) // [2,3,4]

Functions

curry

Auto curries a function so that some or all of the arguments can be supplied.

    import { curry } from 'koeus'

    const add = (x,y) => x + y
    const curriedAdd = curry(add)

    const someArguments = add(1)(2)
    const allArguments = add(1,2)

pipe

Composes unary functions from left to right.

    import { pipe, curry } from 'koeus'

    const pipeline = pipe(x => x + 1, x => x + 2) // x => x + 3

    const four = pipeline(1) // 4

    // If you have a function with multiple arguments that you want to pipe
    // you can curry the function and partially apply it to make it an unary function.

    //ex:
    const add  = curry((x,y) => x + y)
    const addOne = add(1)
    const addTwo = add(2)
    const addThree = pipe(addOne, addTwo)
    const four = addThree(1) // 4

K

Accepts two arguments and ignores the second you give it. The name comes from the K combinator in combinatory logic.

    import { K } from 'koeus'

    const four = K(4,2) // 4

Id

Unary function that returns the argument you give it.

    import { Id } from 'koeus'

    const x = Id(1) // 1

Logic

combineAnd

Folds a list of booleans using logical conjunction (AND)

    import { combineAnd } from 'koeus'

    const t = combineAnd([true,true,true]) // true
    const f = combineAnd([true,true,false]) // false

combineOr

Folds a list of booleans using logical disjunction (OR)

    import { combineOr } from 'koeus'

    const t1 = combineOr([true,true,true]) // true
    const t2 = combineOr([true,false,true]) // true
    const f = combineOr([false,false,false]) // false

combinePreds

Takes a list of predicates and returns a predicate that's the conjunction of all of them.

    import { combinePreds } from 'koeus'

    const preds = combinePreds(x => x % 2 === 0, x => x < 10)
    const result = [1,2,14,4].filter(preds) // [2,4]

Lists

map

Accepts a function, then a functor (in this case a list) and runs the function over the list.

    import { map } from 'koeus'

    const Box = x => ({
        map: f => Box(f(x))
    })

    const addOne = map(x => x + 1) // collection => collection.map(x => x + 1)

    const mapList = addOne([1,2,3]) // [2,3,4]
    const mapBox = addOne(Box(1)) // Box holding the value 2

flatten

Flattens a list one level.

    import { flatten } from 'koeus'

    const flattened = flatten([[2],[3],[4]]) // [2,3,4]

deepFlatten

Flattens a list recursively n-depth levels.

    import { deepFlatten } from 'koeus'

    const flattened = deepFlatten([[2, [3]],[3,[3,4]],[4]]) // [2,3,3,3,4,4]

partition

Take a predicate, then a list and returns an array of two arrays, the first of which passes the predicate passed in, the second which does not.

    import { partition } from 'koeus'

    const arr = [1,2,3,4]
    const isEven = x => x % 2 === 0
    const partitioned = partition(isEven)(arr) // [[2,4],[1,3]]

Objects

entries

Takes an object, then returns an array containing the values from it's keys, one level deep.

    import { entries } from 'koeus'

    const obj = { id: 2, name: 'Will'}
    const vals = entries(obj) // [2, Will]

Transducers

transMap

Takes a transformation function, then returns a reducing function to pass to a reduce function on a list.

    import { transMap } from 'koeus'

    const reducingFunction = transMap(x => x + 1)

    const newArray = [5,5].reduce(reducingFunction, []) // [6,6]

transFilter

Takes a predicate function, then returns a reducing function to pass to a reduce function on a list.

    import { transMap } from 'koeus'

    const reducingFunction = transFilter(x => x % 2 === 0)
    const result = [5,2,10].reduce(reducingFunction, []) // [2,10]