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Algebraic Semantics of Imperative Programs presents a self-contained and novel "executable" introduction to formal reasoning about imperative programs. The authors' primary goal is to improve programming ability by improving intuition about what programs mean and how they run. The semantics of imperative programs is specified in a formal, implemented notation, the language OBJ; this makes the semantics highly rigorous yet simple, and provides support for the mechanical verification of program properties. OBJ was designed for algebraic semantics; its declarations introduce symbols for sorts and functions, its statements are equations, and its computations are equational proofs. Thus, an OBJ "program" is an equational theory, and every OBJ computation proves some theorem about such a theory. This means that an OBJ program used for defining the semantics of a program already has a precise mathematical meaning. Moreover, standard techniques for mechanizing equational reasoning can be used for verifying axioms that describe the effect of imperative programs on abstract machines. These axioms can then be used in mechanical proofs of properties of programs. Intended for advanced undergraduates or beginning graduate students, Algebraic Semantics of Imperative Programs contains many examples and exercises in program verification, all of which can be done in OBJ.

This paper unveils and motivates an ambitious programme of hidden algebraic research in software engineering. We begin with an outline of our general goals, continue with an overview of results, and conclude with a discussion of some future plans. The main contribution is powerful hidden coinduction techniques for proving behavioural correctness of concurrent systems, and several mechanical proofs are given using OBJ3. We also show how modularization, bisimulation, transition systems, concurrency and combinations of the functional, constraint, logic and object paradigms fit into hidden algebra.

This paper provides a tutorial introduction to a constructive theory of types based on, but incorporating some extensions to, that originally developed by Per Martin-L6f. The emphasis is on the relevance of the theory to the construction of computer programs and, in particular, on the formal relationship between program and data structure. Topics discussed include the principle of propositions as types, free types, congruence types, types with information loss and mutually recursive types. Several examples of program development within the theory are also discussed in detail.