Promises are monads. `ok` is `return :: a -> Promise a` and `then` is `bind :: Promise a -> (a -> Promise b) -> Promise b`. All other behavior arises from that,

Promises are monads. `ok` is `return :: a -> Promise a` and `then` is `bind :: Promise a -> (a -> Promise b) -> Promise b`. All other behavior arises from that, the monad laws, and the operations throw :: Error -> Promise a reject :: Promise a -- I guess, not sure of the semantics here