Making the World Safe for Garbage Collection

This paper describes the formal specifications of garbage collection in the programming language Cedar Mesa. They were developed as part of the process of identifying a safe subset of Mesa for which garbage collection was possible. The purpose of the specifications was to provide a precise definition of safety, along with criteria for checking the safety of proposed language features. Thus the specifications had to characterize the “invisibility ” of the collector, as well as describe the services it provides. A beneficial effect of the specification effort was that the process of constructing the specifications led to a number of discoveries that improved the quality of the language. 1