lazy.stream.js

var Id = v => ({v: v,map: f => Id(f(v)) });

var CoFreeF = (a, next) => ({
  a: a,
  next: next,
  extract: () => a,
  map: g => CoFreeF(g(a), () => next().map(x=>x.map(g))),
});

var f = n => CoFreeF(n + 1, () => Id(f(n + 1)));

var stream = f(0);
console.log(stream)

var x = stream.next().v.next().v.map(x => x * 2).next().v;
console.log(x);