State Constraints and Pathwise Decomposition of Programs

A state constraint is a new programming construct designed to restrict the domain of definition of a program. It can be used to decompose a program pathwise, i.e., to divide the program into subprograms along the control flow, as opposed to divide the program across the control flow when the program is decomposed into functions and procedures. As the result one can now construct and manipulate a program consisting of one or more execution paths of another program. This paper describes the idea involved, examines the properties of state constraints, establishes a formal basis for pathwise decomposition, and discusses their utilities in program simplification, testing, and verification.