JS: List Implementation

lists.js

const cons = (x, y) => f => f(x, y);
const car = f => f((x, y) => x);
const cdr = f => f((x, y) => y);

function list() {
  const h = Array.prototype.slice.call(arguments, 0)[0];
  const t = Array.prototype.slice.call(arguments, 1);
  if (h == null) {
    return cons(null, null);
  }
  return cons(h, list.apply(this, t));
}

const head = lst => car(lst);
const tail = lst => cdr(lst);
const isEmpty = lst => head(lst) == null;

const map = (lst, fn) => 
  isEmpty(lst) ? 
      list() : 
      cons(fn(head(lst)), 
           map(tail(lst), fn));
    
const reduce = (lst, acc, fn) => {
  const iter = (items, result) => {
    if (isEmpty(items)) {
      return result;
    }
    return iter(tail(items), fn(head(items), result));
  };
  return iter(lst, acc);
};

const toString = lst => 
  reduce(lst, 
         null, 
         (it, acc) => 
           (acc == null ? '' : acc + ', ') + it);

const toArray = lst =>
  reduce(lst,
        [],
        (it, acc) => acc.concat(it));

const reverse = lst =>
  reduce(lst,
        list(),
        (it, acc) => cons(it, acc));

const lst = list(1,2,3,4,5,6);

console.log(toString(map(lst, x => x * 3)));
console.log(reduce(lst, 0, (it, acc) => acc + it));
console.log(toString(lst));
console.log(toArray(reverse(lst)));