Reasoning about recursive procedures with parameters

Abstract

In this paper we extend the model of program variables from the Refinement Calculus [2] in order to be able to reason more algebraically about recursive procedures with parameters and local variables. We extend the meaning of variable substitution or freeness from the syntax to the semantics of program expressions. We give a predicate transformer semantics to recursive procedures with parameters and prove a refinement rule for introduction of recursive procedure calls. We also prove a Hoare total correctness rule for our recursive procedures. These rules have no side conditions and are easier to apply to programs than the ones in the literature. The theory is built having in mind mechanical verification support using theorem provers like PVS [18] or HOL [11].