takeTruthy.js

const compose = (f, g) => a => f(g(a));
const takeUntil = (f, xs) => xs.slice(0, xs.findIndex(f));
const id = a => a;
const not = a => !a;
const takeWhile = (f, xs) => takeUntil(compose(not, f), xs);
const takeTruthy = xs => takeWhile(id, xs);

const compose = (f, g) => a => f(g(a));
const pipe = (...xs) => xs.reverse().reduce(compose);

const walk = (f, [x, ...xs], ys = []) => {
  const y = f(x)
  return y ? walk(f, xs, ys.concat(y)) : ys
}
// const walk = (f, [x, ...xs], ys = []) => (x = f(x)) ? walk(f, xs, ys.concat(x)) : ys