FP data structure: map

list.js

const cons = (a, b) => p => p ? a : b;
const car = pair => pair(1);
const cdr = pair => pair(0);

const shift = xs => x => cons(x, xs);
const length = xs => typeof xs === 'function' ? 1 + length(cdr(xs)) : 0;
const get = xs => index => index ? get(cdr(xs))(index - 1) : xs;

const list1 = cons(1, cons(2, 3));
car(list1);
car(cdr(list1));
length(list1);

const list2 = shift(list1)(0);
car(list2);
length(list2);

map.js

const map = () => null;
const set = map => (key, value) => q => q === key ? value: map
const get = map => key => typeof map === 'function' ? get(map(key))(key) : map;


const map1 = set(map)('key1', 1);

get(map1)('key1')
get(map1)('key2')

const map2 = set(map1)('key2', 2)

get(map2)('key1')
get(map2)('key2')

const map3 = set(map2)('key1', 3)

get(map3)('key1')
get(map3)('key2')