Teachpacks for How to Design Programs

# Elevator

### elevator.ss

The teachpack `elevator.ss` implements an elevator simulator. It displays an eight-floor elevator and accepts mouse clicks from the user, which are translated into service demands for the elevator. The teachpack provides a single operation:

- `run : NextFloor -> void`
  that is, it consumes an elevator controller and returns nothing .
  Sample session: First define a function that consumes the current state of the elevator (three arguments) and returns a number between 1 and 8. Here is a non-sensical definition:
  `(define (controller x y z) 7)`
  It moves the elevator once, to the 7th floor.
  Second, set the teachpack to `elevator.ss` execute and run:

      > (run controller)
      >