prelude-js

import compose from 'preludejs/Func/compose'
import curry from 'preludejs/Func/curry'
const add = curry((a: number, b: number) => a + b)
const double = (x: number) => x * 2

// Compose runs right-to-left (double after add(2))
const addThenDouble = compose(double, add(2))

const result = addThenDouble(3) // => 10
       
const result: number

import compose from 'preludejs/Func/compose'
import filter from 'preludejs/List/filter'
import map from 'preludejs/List/map'
const isEven = (x: number) => x % 2 === 0
const double = (x: number) => x * 2

// Chain filter then map with right-to-left compose — point-free
const doubleEvens = compose(map(double), filter(isEven))

const result = doubleEvens([1, 2, 3, 4]) // => [4, 8]
       
const result: number[]

import get from 'preludejs/Obj/get'
import merge from 'preludejs/Obj/merge'
const user = { name: 'ada', role: 'admin' }

// get is key-first and curried
const role = get('role', user) // => "admin"
      
const role: string

// merge — later sources win
const owner = merge(user, { role: 'owner' }) // => { name: "ada", role: "owner" }
      
const owner: {
    name: string;
    role: string;
} & {
    role: string;
}

import camelize from 'preludejs/Str/camelize'
import words from 'preludejs/Str/words'
const camel = camelize('prelude-js-library') // => "preludeJsLibrary"
      
const camel: string

const list = words('hello functional world') // => ["hello", "functional", "world"]
      
const list: string[]

import compose from 'preludejs/Func/compose'
import filter from 'preludejs/List/filter'
import map from 'preludejs/List/map'
import sortBy from 'preludejs/List/sortBy'
import get from 'preludejs/Obj/get'
import capitalize from 'preludejs/Str/capitalize'
type User = { name: string; age: number }

const users: User[] = [
  { name: 'ada', age: 36 },
  { name: 'linus', age: 12 },
  { name: 'grace', age: 31 },
]

// adults only, oldest first, names capitalized — composed right-to-left
const summarize = compose(
  map((u: User) => capitalize(get('name', u))),
  sortBy((u: User) => -u.age),
  filter((u: User) => u.age >= 18),
)

const adults = summarize(users) // => ["Ada", "Grace"]
       
const adults: string[]