unfoldWith.js

// Classic array unfold that works with functions that produce
// reasonably-sized output arrays.
export const unfoldWith =
    f => x =>
        _unfold(f, [], x)

// Recursive unfold function. Will overflow stack for very, very large unfolds.
// f should return null, if done, or return [ curr, next ] values, if not.
const _unfold =
    (f, acc, value) => {
        const result = f(value)
        if (!result) return acc
        const [ curr, next ] = result
        return _unfold(f, acc.concat(curr), next)
    }