FunZ: An Intermediate Specification Language

During the last few years, the field of software engineering has witnessed an increased interest in formal methods and software reuse. At the same time, functional programming languages, often espoused as rapid prototyping tools, have begun to enjoy more mainstream usage. Assuming that these trends continue, software developers will need improved methods to transform existing specifications into functional implementations. In this paper, we discuss the intermediate specification language FunZ, an integral part of a methodology to produce purely functional programs from Z specifications. To illustrate the concepts of FunZ, we specify the design of a simple software system using both the Z notation and that of FunZ. FunZ itself is best described as an extension of Haskell, yet the language also retains a Z-like flavour in that it contains notational conventions similar to those of standard Z and several object-oriented variants. In addition, software design with FunZ parallels the activity in Z except that each step has functional overtones to better accommodate a final implementation in a purely functional language.