1.js

class Nil {}
class Cons { constructor( head,   tail) { Object.assign(this, {  head,   tail }); } };
class Pair { constructor(first, second) { Object.assign(this, { first, second }); } };

const _1 = () => 1;
const _2 = () => 2;
const _3 = () => 3;

const nil = () => new Nil();
const cons = (head, tail) => () => new Cons(head, tail);
const pair = (first, second) => () => new Pair(first, second);

const toArray = arr => {
  const arr_ = arr();
  
  if (arr_ instanceof Nil) {
    return [];
  }
  
  return [arr_.head(), ...toArray(arr_.tail)];
}

const max = (a, b) => () => {
  const a_ = a();
  const b_ = b();
  return a_ > b_ ? a_ : b_;
}

const repMax = (arr, rep) => {
  const arr_ = arr();
  
  if (arr_ instanceof Nil) {
    return pair(rep, nil);
  }
  
  const head_ = arr_.head();
  const tail_ = arr_.tail();
  
  if (tail_ instanceof Nil) {
    return pair(() => head_, cons(rep, nil));
  }
  
  const result_ = repMax(() => tail_, rep)();
  const m = max(result_.first, () => head_);
  return pair(m, cons(rep, result_.second));
}

const doRepMax = arr => {
  const result_ = repMax(arr, () => result_.first())();
  return result_.second;
}

const x = cons(_1, cons(_3, cons(_2, nil)));
const y = doRepMax(x);
console.log(toArray(y)); // [3, 3, 3]