Advanced Functional Patterns — Series 3

const ok = (v) => ({ ok: true, v });
const err = (e) => ({ ok: false, e });

const map = (r, f) => (r.ok ? ok(f(r.v)) : r);
const chain = (r, f) => (r.ok ? f(r.v) : r);

const parse = (s) => (Number.isNaN(Number(s)) ? err('not a number') : ok(Number(s)));
const recip = (n) => (n === 0 ? err('divide by zero') : ok(1 / n));

console.log(JSON.stringify(chain(map(parse('4'), (n) => n - 4), recip)));
console.log(JSON.stringify(chain(parse('x'), recip)));

const trampoline = (fn) => (...args) => {
  let r = fn(...args);
  while (typeof r === 'function') r = r();
  return r;
};

const sum = trampoline(function rec(n, acc = 0) {
  return n === 0 ? acc : () => rec(n - 1, acc + n);
});

console.log(sum(100000));

const addCPS = (a, b, k) => k(a + b);
const sqCPS = (n, k) => k(n * n);

const out = [];
addCPS(2, 3, (sum) => sqCPS(sum, (sq) => out.push(sum, sq)));

console.log(out.join(','));