Ada exception handling: an axiomatic approach

Abstract

A method of documenting exception propagation and handling in Ada programs is proposed. Exception propagation declarations are introduced as a new component of Ada specifications, permitting documentation of those exceptions that can be propagated by a subprogram. Exception handlers are documented by entry assertions. Axioms and proof rules for Ada exceptions are given. These rules are simple extensions of previous rules for Pascal and define an axiomatic semantics of Ada exceptions. As a result, Ada programs specified according to the method can be analyzed by formal proof techniques for consistency with their specifications, even ff they employ exception propagation and handling to achieve required results {i.e., nonerror situations}. Example verifications are given.

Influences on the design of exception handling ACM SIGSOFT project on the impact of software engineering research on programming language design

“…The Rationale emphasizes that the designers wanted to being able to prove the correctness of programs [22] and to optimize programs with exceptions. These properties led to the rejection of the resumption model which renders both of these difficult.…”

Proceedings of the IDA Workshop on Formal Specification and Verification of Ada (Trade Name) (1st) Held in Alexandria, Virginia on 18-20 March 1985.

“…Loops can also be left by executing a return statement or by the raising of an exception. These in principle present no special difficulties and [Luckham and Polak, 1980 …”

“…The rules for procedure calls (see [Luckham and Polak, 1980]) make some assumption about the parameter passing mechanism. ARM 11.6, Exceptions and Optimization [Cohen, 1985] observes that optimizing compilers which reorganize computations present difficult problems to verifiers.…”

Program verification at Stanford

“…We have made some progress in the direction of providing a specification language for new problem domains by developing a n axiomatic semantics for modules (Ada packages) and error handling (Ada exceptions) [4,5,6] . We are currently attempting t o design a highly useable, well-engineered specification language, called ANNA, that matches Ada concepts and programmin g constructs .…”