A function cannot remember how often it was called or what its previous arguments where. A functional program can only represent physical changes by incorporating time. Both are major impediments to formulating programs in a concise manner.

To address this problem, the course motivates and covers the design of imperative Scheme programs, especially,

1. history-tracking programs,

2. state-reflecting (simulation) programs, and

3. programs that mutate compound data values, especially vectors.