> One of the biggest differences is that you can perform computations
> with promises - the result is another promise, etcetera. Only when you
> really really really need to do something acute to the promise you end
> up with, you block waiting for all the work to finish.

IIRC there is no way of a blocking wait for promises in E, because
this against the principles of E and could result in a deadlock. But
there are no deadlocks in E because there's just one thread and no
blocking.

All you can do is register a callback that gets evaluated when the
promise is fulfilled.