reduce, map and filter one-liners. Just because.

reduce-map-filter.js

const reduce = reducer => memo => ([first, ...rest]) =>
  first ? reduce(reducer)(reducer(first)(memo))(rest) : memo

const map = f => arr =>
  reduce(mapReducer(f))([])(arr)

const filter = f => arr =>
  reduce(filterReducer(f))([])(arr)

const mapReducer = f => element => memo =>
  memo.concat(f(element))

const filterReducer = f => element => memo =>
  f(element) && memo.concat(element) || memo

const addReducer = a => b => a + b
const add1Reducer = addReducer(1)
const isEven = a => a % 2 == 0

const items = [1,2,3,4,5]

console.log(reduce(addReducer)(0)(items)) //=> 15
console.log(map(add1Reducer)(items))      //=> [2,3,4,5,6]
console.log(filter(isEven)(items))        //=> [2,4]