I developed a large chip that would render a graphic description called Picture Model into high-resolution anti-aliased pixels. I used a circuit design style where transistors would switch open or closed to guide charge around the design performing computations as it went.
I loaded the complete design into a switch simulator written in c and then exercised all of the design's functions with lisp functions evaluated by a small interpreter imbedded in the simulator for just this purpose.
Both the circuit simulator and the lisp interpreter were small enough that they could be understood. This was important if I were to use the model effectively and understand its results.
I used lisp structures as an organizing principle in a c program again building a Circuit Structure Inverter for our IC Design Tools group.