The images at the top and bottom of this post were made in Processing and were inspired by some of the exercises from the 1972 book Principles of Two-Dimensional Design by Wucius Wong.
Forty years ago this book introduced a language for thinking and talking about the then emerging world of modern design. Today it could also be a source of exercises in basic programming, particularly well-suited for Processing.
Wong's later book, Principles of Three-Dimensional Design includes really nice examples of geometric sculpture, many based on polyhedral forms.