1.js

const B = f => g => x => f(g(x));
const K = a => b => a;
const I = a => a;

const toPair = p => p(a => b => ({ first: a, second: b }));
const toNumber = n => n(x => x + 1)(0);
const toArray = l => l(x => xs => [x, ...xs])([]);
const toBoolean = b => b(true)(false);

const pair = a => b => f => f(a)(b);
const first = p => p(K);
const second = p => p(K(I));

const _true = K;
const _false = K(I);

const succ = n => s => z => s(n(s)(z));
const add = n => m => s => z => n(s)(m(s)(z));
const mul = n => m => s => z => n(m(s))(z);

const _0 = s => z => z;
const _1 = succ(_0);
const _2 = succ(_1);
const _3 = succ(_2);
const _4 = mul(_2)(_2);

const pred = n => s => z => second(n(p => pair(s(first(p)))(first(p)))(pair(z)(z)));
const isZero = n => n(K(_false))(_true);

console.log(toNumber(pred(_4))); // 3
console.log(toBoolean(isZero(_0))); // true
console.log(toBoolean(isZero(_1))); // false
console.log(toNumber(add(_1)(_3))); // 4
console.log(toNumber(mul(_4)(_4))); // 16

const nil = fold => init => init;
const cons = x => xs => fold => init => fold(x)(xs(fold)(init));
const append = x => l => l(cons)(cons(x)(nil));
const map = f => l => l(B(cons)(f))(nil);

const list = cons(_1)(cons(_2)(cons(_3)(nil)));
const list2 = append(_4)(list);

console.log(toArray(map(toNumber)(list2))); // [1, 2, 3, 4]

const range = n => second(n(p => pair(succ(first(p)))(append(first(p))(second(p))))(pair(_0)(nil)));

console.log(toArray(map(toNumber)(range(_4)))); // [0, 1, 2, 3]

const factorial = n => map(succ)(range(n))(mul)(_1);

console.log(toNumber(factorial(succ(_4)))); // 120