/**
 * Returns a Promise which resolves with a value in form of a tuple.
 * @param promiseFn A Promise to resolve as a tuple.
 * @returns Promise A Promise which resolves to a tuple of [error, ...results]
 */
export function tuple (promise) {
  return promise
    .then((...results) => [null, ...results])
    .catch(error => [error])
}

/**
 * Returns a function which creates a tuple-ful Promise.
 * @param fn A function to create a tuple from.
 * @returns A function which creates a tuple from `fn`.
 */
export function tuplify (fn) {
  return function tupleFn (...args) {
    return tuple(fn(...args))
  }
}