When toying around with implementing FRP one thing I've found that is confusing is what to do with the past? Basically, my understanding was that I would be able to do this with a Behaviour at any point:
beh.at(x) // where time x < now
This seems like it could be problematic performance wise in a case such as this:
val beh = Stepper(0, event) // stepwise behaviour
Here we can see that to evaluate the Behaviour in the past we need to keep all the Events and we will end up performing (at worst) linear scans each time we sample.
Do we want this ability to be available or should Behaviours only be allowed to be evaluated at a time >= now? Do we even want to expose the at
function to the programmer?