Lifting promises.

promises.md

Idea: programming with a promise for an a as if it were "more or less" an a. That is, we don't want to have to change our programming style too much when transitioning from dealing with actual as to promises for as.

function lift(f) {
  return function(...promises) {
    return Promise.all(promises).then(values => f.apply(null, values))
  }
}

lift takes a function f that operates on "regular" arguments. It promotes it to a function that operates on promised arguments, and it promises whatever f would have done with them.