extend future.rs with helpfull methods

I am new to Rust and i don't have time to touch it now. But i want to contribute to the project even with ideas.
The future abstraction is very similar to "Promise" if not the same. I like if someone implements promise features for futures
like the following methods/functions witch allow one them to compose better.
fn when(a: Future<A>, b: Future<B>) -> Future<(A, B)>

method:
fn then(self: Future<A>, &fn (A) -> Future<B>) -> Future<B>