The type signature, with `catch` is something like Either mixed with `IO`, it's just a specific form of continuation[1]. Promises are not _exactly_ like an IO monad because it would not be pragmatic, but it serves the same purpose (controlled side effects and boxing temporal state) in the same way (a bind operator).

If you look at all the examples online for `IO` [2] they all translate 1-1 to promises just fine :)

[1] : http://blog.sigfpe.com/2008/12/mother-of-all-monads.html [2] : for example http://adit.io/posts/2013-04-17-functors,_applicatives,_and_...