Extracting data from a function chain without arrays

Question

This is an advanced topic of

How to store data of a functional chain of Monoidal List?

I am pretty sure we can somehow extract data from a function chain wit

Answer 1

I've gone through the various questions you have but I'm still not sure I entirely understand what you're looking for. On the off chance you're simply looking to represent a linked list, here is a "dumb" representation that does not use clever tricks like overloaded arguments or default parameter values:

const List = (() => {
  const nil = Symbol()

  // ADT
  const Nil = nil
  const Cons = x => xs => ({ x, xs })
  const match = ({ Nil, Cons }) => l => l === nil ? Nil : Cons(l.x)(l.xs)

  // Functor
  const map = f => match({
    Nil,
    Cons: x => xs => Cons(f(x))(map(f)(xs))
  })

  // Foldable
  const foldr = f => z => match({
    Nil: z,
    Cons: x => xs => f(x)(foldr(f)(z)(xs)) // danger of stack overflow!
                                           // https://wiki.haskell.org/Foldr_Foldl_Foldl%27
  })

  return { Nil, Cons, match, map, foldr }
})()

const { Nil, Cons, match, map, foldr } = List
const toArray = foldr(x => xs => [x, ...xs])([])

const l = Cons(1)(Cons(2)(Cons(3)(Nil)))

const l2 = map(x => x * 2)(l)
const l3 = map(x => x * 3)(l2)

const a = toArray(l3)
console.log(a) // => [6, 12, 18]