We have implemented object-oriented hardware design techniques in Fred, using the Flavors language [l], an object-oriented extension of Lisp. Fred supplies design description and evaluation tools for CAD applications: designers write hardware descriptions that are translated by Fred into data structures; the CAD program then uses functions supplied by Fred to measure and manipulate the data structures that represent the design. Fred’s hardware description features encourage a CAD programming style that is a combination of inheritance and constraint propagation.