[mattgreenrocks]

It's a side effect of decoupling. If you don't need to pass the world in to a function, then it is much easier to poke at.

I played with Clojure making a simple pong game, and used this to work on collision detection. I worked on a function called rect-intersects that took in two rectangles. It was much faster to work on than if I'd booted up the game each time.