"Time" in Apparatus

[Ira Joseph Woodhead]

In another topic (Animations) someone mentioned wanting to play out a creation without needing interaction. The given answer was there was no concept of time built-in to Apparatus.

Well, here's a neat thing I stumbled on to. If you create a function F that takes some variable by reference and modifies it, and then define another variable as the result of calling F on some global state, the state will be modified over and over, evolving by discrete steps. Each time state is modified, it must be reevaluated, and the reevaluation modifies it again etc.

Here is a complete example:

Notice "step" is defined initially as 0, but keeps updating. Interesting thing about this is it is controllable by how much you move the mouse cursor around. I gather this must be because there is only one thread for both interaction and program eval, and it executes functions once between interaction events.

I found this example when I was making a queue simulator and intended to make a slider to indicate some time value, but the function I had written to advance the state was already acting to find equilibrium without my having to program any time steps. 

PS I love this tool, it's like programmable legos!