Purely functional implementation of streams in JavaScript borrowed from SICP

purely-functional-streams.js

const EMPTY = null;
console.clear();
var naturals$ = Naturals()
var firstFive$ = take(5, naturals$)
applyEach(
  n => console.log(n),
  firstFive$
)

// 1 2 3 4 5

function Naturals(startAt=1) {
  return unshift(
    startAt,
    defer(Naturals, startAt + 1)
  )
}

function take(n, s) {
  if (isEmpty(s) ||
      n < 1) return empty()
  return unshift(
    head(s),
    defer(take, n - 1, tail(s))
  )
}

function defer(f, ...args) {
  return function() {
    return f.apply(null, args)
  }
}

function applyEach(f, s) {
  if (isEmpty(s)) return empty()
  f( head(s) )  // side-effect
  return applyEach(
    f,
    tail(s)
  )
}

function head(s) {
  return s('head')
}

function tail(s) {
  return demand( s('tail') )
}

function demand(f) {
  return f();
}

function unshift(head, tail) {
  return function get(ref) {
    switch (ref) {
      case 'head': return head;
      case 'tail': return tail;
    }
  }
}

function empty() {
  return EMPTY;
}

function isEmpty(s) {
  return s === EMPTY;
}